Now I can see why I never really "got" concepts like force, but rather memorized the treatment, and pretended to be comfortable with it, as presumably the teacher was also doing. The unsatisfactory feeling that the science was somehow settled and accepted, but I couldn't understand it, is maybe why I pursued mathematics, instead of physics. I'll make sure to teach my kids that it's ok (and desirable) to admit a lack of understanding, even on the most basic and common concepts.
This guy, dialect, is very misleading. Force is a fundamental property and to understand force, you need to understand what is wave because if you really want to understand force you need to understand how action was invented. And if you can understand all of these then you will be able to grasp quantum mechanics and that will lead you to force and then you will understand action is force. This guy creates a loop hole by not telling you the full story. I would advise you to tell your children to earn more knowledge and not to become happy by not being able to determine Truth and false. Even math uses zfc that states that numbers are empirical not something that was given to you from heavens. Thus these kind of channels are cheap philosophy that keeps hiding the evidence from you and tries to say wow that's cool. Henry Poincare was an intuitionist mathematician which is very bad. To be a good philosopher you need to be a skeptic, a logician and then an intuitionist, if i say wow the sea is a projection of earth's sky and show some evidence that supports my line. Will you start believing me? If you do then sad. But a sensible person will try to find counter evidence and if he finds that then that means either i am wrong or i was not being dishonest rather a biased person. That's what is happening sadly with these kinds of channels. When we talk about F=ma we mean if F exists only then m and a exists and if a exists only then m and F exists and if m exists only then F and a exists. So all of them are required for everyone's existence and general relativity never showed force doesn't exist rather it showed force exists in a different kind, like geometry okay. I guess i was clear enough.
@@dialectphilosophy stop giving cheap advice man. Rather read what i am saying, This guy, dialect, is very misleading. Force is a fundamental property and to understand force, you need to understand what is wave because if you really want to understand force you need to understand how action was invented. And if you can understand all of these then you will be able to grasp quantum mechanics and that will lead you to force and then you will understand action is force. This guy creates a loop hole by not telling you the full story. I would advise you to tell your children to earn more knowledge and not to become happy by not being able to determine Truth and false. Even math uses zfc that states that numbers are empirical not something that was given to you from heavens. Thus these kind of channels are cheap philosophy that keeps hiding the evidence from you and tries to say wow that's cool. Henry Poincare was an intuitionist mathematician which is very bad. To be a good philosopher you need to be a skeptic, a logician and then an intuitionist, if i say wow the sea is a projection of earth's sky and show some evidence that supports my line. Will you start believing me? If you do then sad. But a sensible person will try to find counter evidence and if he finds that then that means either i am wrong or i was not being dishonest rather a biased person. That's what is happening sadly with these kinds of channels. When we talk about F=ma we mean if F exists only then m and a exists and if a exists only then m and F exists and if m exists only then F and a exists. So all of them are required for everyone's existence and general relativity never showed force doesn't exist rather it showed force exists in a different kind, like geometry okay. I guess i was clear enough.
I have not even started watching the video, but I am going to give you a like because of the mere fact that you chose to do a video on such a seemingly basic and simple concept. Topics like these are usually hand-waved away by teachers and professors alike as if they don't warrant a deeper explanation and have already been logically figured out by minds greater than our own. As someone who has always felt dumb for questioning the most basic of concepts, especially in physics, it is very refreshing to see that you have made explainers on these topics and taken them with enough sincerity in an attempt to properly formalise the most fundamental notions
Feel force, feel time, feel space? If you delve on that, you can doubt everything, not just forces. Stay simple. With clocks we measure time intervals. With rules we measure space distances. With springs we measure force differences. In F=ma, we can use clocks and rules to evaluate the acceleration, a spring to evaluate the force, and the thing we really need to assume to exist beyond our measurement instruments is mass.
But you didn’t understand what the video was talking about. Force, unlike the rest of the above, is introduced not as an independent physical quantity, but as the product of acceleration and mass. By the way with spring you can only measure spacial displacement of this spring
@@noavailablenamesatall My body is build using electromagnetic interactions. With these I am endowed with senses that can see, hear, smell, taste, and touch. When you shake my hand, my body feels the pressure. I can also watch accelerations. In F=ma the only thing that I cannot see, hear, smell, taste or touch is mass. That's what I need to assume.
@@josecastro4465 You can see and touch a mass; when you see, touch, weight a mass you are measuring it, the same is for the Force. If you see a video of an accelerometer that is changing somehow you cannot know what is happening unless you have some "context" knowledge. At 5:05 it could also be that the entire room is rotating and you, that are watching the video, will not be able to see it. I will add that a ruler is a "reference frame" relative to which we are comparing lengths of objects. A notch of a ruler is the reference frame relative to which we measure the ruler...
@@josecastro4465 The video demonstrates the relativity of phenomena such as force and acceleration, which are postulated as absolute. You will always feel a relative difference in force depending on how your sensory system is calibrated
@@noavailablenamesatall in practical terms then relative is all the matters. Having played football for many years, believe there’s a tremendous amount of force on the field lol.
Inside the closed room the person is standing and the accelerometer is hanging from the ceiling. That can mean atleast two things: 1. There is a force that is pointing downwards. 2. The person and the ball are arranged inside the room in such a way in free space free from any external force.( let us assume that the only matter left in the universe is the concrete room with the things inside it) In both the situation direction of acceleration can be observed. Situation 1. The person may fall if the acceleration is high enough. Situation 2. In case of an acceleration, the person will move towards a wall if the shoes he's wearing aren't fixed to the floor. If the shoes he is wearing are fixed to the floor , he will rotate and bang his head on a wall or floor.
Having watched the entire video, I think your point is just: "Force and acceleration cannot be defined without outside information." But we can define: "If light always travels in a straight line in this frame of reference, then the frame of reference is inertial." There is nothing wrong with this definition. If anyone has a different thought, rebuttals are welcome.
If you are on a spaceship falling towards earth via gravity, you are in free fall and a light beam would travel in a straight line in your reference frame. Yet for an observer on earth you are accelerating.
@@dragoscoco2173 No, because the effects of gravity, the observer on earth will see both the light on earth and the light in spaceship curved. The observer in spaceship won't see any of the light curve because their acceleration and gravity cancel out. The observer on earth accelerated. not the spaceship.
@@dragoscoco2173 But because of gravity, the space flow towards the center of the earth. So the observer on earth must accelerate to stay stationary relative to the earth. I think that means the earth observer have "real" acceleration. (Thay do observes light turning. By general relativity, gravity and acceleration are the same.)
@@babbrian7033 There are some problems though. "because of gravity, the space flow towards the center of the earth" that is just a visualization of an unknown process. Also remember that the spaceship has it's own gravity and pulls the Earth towards it too, complicating the matter. I am more in the Forces are real camp, but find that gravity acting on every atom, means that it will be hard to impossible to tell if you experience it unless you view your surroundings. Acceleration acts only on the parts that pull or push you creating pressure that can be felt. They are the same but one is more evenly spread.
Some broad thoughts im thinking right now: say, 1.) Force concerns how mass/matter reacts to motion. 2.) Matter/mass units can't (in essence) occupy the exact same space. So if you have multiple mass units, they are a distance apart from eachother. 3.) Max speed is C, so it will always take time to move mass across space. So you have a blob of mass spread across space, another mass comes in contact with the blob (there must be motion involved). They can't occupy the same space. 'internal pressure' of a mass or w/e will be in an equilibrium if outside conditions stay the same. Now after the collision, at the point of contact theres a bunch of back and forth of pressure-waves I guess.. It takes time for pressure to spread acros the blob of mass. This squeezing and stretching of the volume units of mass, because of localised pressure changes inside of the blob, are what they mean by 'feeling force'. If you happen to read this and think im an idiot its entirely possible. Got no real physics/math background. Would like to know why this would be wrong so I can see where i'm thinking wrong.
"Pressure" is defined as force per unit of surface. So, we do not really extend our intuition here by adding pressure to the equation. It's still about the nature of force, defined as the product of mass and its acceleration, i.e., its change of momentum, which we call its impulse. The problem is that we need to presume an inertial frame of reference to be able to define the background at which this acceleration can be observed. This also applies to light. We say that light in a vacuum travels at its maximum speed. But that is under the condition of a local frame, where space-time is considered to be undisturbed. Over larger distances, the speed of light does not necessarily equal 'c', the well-known value that we normally mention as the speed of light.
3:06 Mass is not directly observable either. Mass can only defined with respect to an inertial frame. This is easy to fix in Newtonian physics because accelerations are invariant under Galelian transformations. The fix in relativity is more difficult, and leads directly to E=mc^2.
Summary 3: To find out inertial vs non-inertial frames NO REFERNCE TO ANYTHING OUTSIDE THE FRAME IS NECESSARY. Experiments confined within the frame are good enough to tell us if we are in an inertial frame or a non-inertial frame.
Finally, at this moment, my spring have been awakened. It feels the force. Seriously "Force" does not have be felt. One of the easiest way to "observe" the force is the use of spring as a measure. In my humble opinion, spring does not "feel" anything. It does not have any knowledge about "inertial-ness". It also doesn't observe an acceleration, too. It's just a thing. It's different from me and my cat. But it perfectly & precisely react to the Force. How do you explain this? Quantum mechanics doesn't even bother the force!!??? man, quantum world is FULL of forces. It even tells how different kind of forces are transmitted through the particles. It doesn't covers Einstein's gravity yet but gravity is actually included in the theory as graviton (undiscovered yet, though). Okay, if you think, acceleration is caused by the "transformation of reference frame" you says, what about the "force" caused by the magnetic fields? how it's related to the "reference frame"? there is no acceleration but electron moves! I really liked your clam on "twin paradox" (at least half of it) but this is total nonsense. I agree that there are lots of interpretation of the laws of the physics as long as it consistent with the theory. But if you want to make your point, you should explain why your interpretation is better than the others. For example, Everett introduce his new interpretation for quantum mechanics to eliminate Von Neumann's projection. Because as long as we have it, we can't apply quantum theory to the universe itself where there is no "outside". He did not say, there are thousand of universe correspond to every quantum state...he said this is the reasonable assumption to improve the theory. So what is the point of your interpretation...no offence but seriously you need more research on the topic your interested in!!! Finally, this is the last claim. The reality of the variable in the physics law is actually questionable. In other words, the force may not be the "real thing". It only appears in the theory to clarify the relationship of the variable, that's all. But one thing for sure is, as I stated at the first of this comment, you can measure it actually. Therefore, I think it exists. But this is not a physics, it totally unrelated to the actual theory. It's more like philosophy than the physics.
An accelerometer such as a spring doesn't resolve the issue of how to measure force, because you are only still measuring something accelerating. As this video discussed, such a measurement has to be paired with additional information not intrinsic to the system in order for the conclusion to be made that a force is present. We discuss this topic further in our "Inertial Frames" video. We are not offering a "new interpretation" of any theory, only pointing out a flaw in the current interpretation. Many interpretations and theories have had their flaws pointed out without new theories being offered up in their place... critical inquiry and skepticism are an important part of the philosophical and scientific process.
@@dialectphilosophy do you not agree that for an object to accelerate, a force has to be applied? And from that we can deduce that a force has been acted upon the spring? Or do you not like the idea that deduction has to be used to come to the solution that a force has been applied? Also, all the examples you have given in this video are situations where objects have accelerated away from type of inertial frame. Force can be applied without the need to for objects to accelerate, as I can squish an egg in my hand with force without the egg changing it's position. Furthermore, the situation where a person is in a empty room and sees an accelerometer change position and thinking that maybe it's just being affected by a magnet and not that a force is being acted on the building seems flawed. As I can exclaim that the moon is made out of cheese but that doesn't change any facts what the moon is really made out of. I don't know, if you could come with counter arguments to my comments, maybe that would make me understand what you are trying to say.
@付和雷同 One of the fundamental forces, or interactions, such as strong, weak, and electromagnetic, is not the same as a specific quantitative force, the F in Newton's F = ma. As far as gravitons are concerned, even if they exist it may never be possible to discover them.
I think the point is that a spring is now essentially a 3rd observer. With only 2 objects its not possible to tell, which is why I think the more simple explanation of two balls going opposite is maybe more valid.
Force is mass * acceleration. So I would look like a dead pancake if a train hit me. But if I sit inside the train im not sure if this is a accurate formula.
As regards to "Can we 'feel' force?" No, we can't -- not because how you explained it, but because "feeling" is a biological phenomenon and in Physics we DO NOT FEEL ANYTHING. We measure things. And let me tell you, YES, we can measure real forces by doing experiments. Of course Einstein's General Relativity has been formulated in such a way that the gravitational force has been done away with by redefining the effect of mass & energy on spacetime and vice versa, thereby bringing accelerated frames due to gravity within the realm of inertial frames of reference. But acceleration of a reference frame due to any other of the 3 forces of nature (as discovered till now) are definitely detectable by simple experiments within the frame of reference.
I get what you're saying but to be fair physics gives rise to feelings and everything else about human experience. Unless you think its some kind of dualistic magic separate from everything else in the universe.
Summary 2: An inertial frame is one such that no mechanical and/or optical experiments conducted completely within the frame can ever tell us about the motion of the frame. Whereas, in a non-inertial frame we can easily detect motion without any reference to outside, just by conducting certain experiments confined within the reference frame.
Fantastic. I hope you will tell us eventually more about the history and resolution of this discrepancy between your vision (Who else shares it? Does it have a name?) and that of the mainstream.
Inertia has nothing to do with "Feeling", it is simply the resistance to change in velocity. Or to put it in better terms it is the resistance to change from an inertial frame of reference. If two objects are accelerating away from each other there would have to be a force involved. This is why you can measure which train is actually accelerating. Since the force is only being applied initially to the train and not the objects inside it, the train will move relative to the objects until the objects come into contact with the train and the force is then applied to them via the wall or seat of the train pushing them forward. This is why if you had two trains in space with a ball inside each of them and only one accelerated away; the ball inside the accelerating train would seem to move relative to its train while the ball in the stationary train would appear to stay still relative to its train. This of course would stop once the acceleration stopped and both trains were moving at a constant velocity relative to each other again. This effect only occurs during the period of acceleration.
Hey thanks for the comment! If you define inertia locally via changes in velocity, then you are stuck at the fact that inertia will be relative, since all motion measurements are coordinative. That's why inertial frames are generally defined in reference to a global system, e.g. frames that aren't accelerating relative to the rest of the universe. In your two-train example, consider instead the frame where the accelerating train is stationary. Now it is the ball which is accelerating away from it, as well as the other train and the other ball. There is no method in the context of the thought-experiment for determining whose acceleration is "more real" than the others. You simply have two distinct but equally valid descriptions of the situation: one description where one train is accelerating away, and another description where two balls and the other train is accelerating. Neither acceleration can be "more correct" until you introduce some further feature distinguishing them.
@@dialectphilosophy So just to make sure I understand your stance; you are disagreeing with the Einstein himself as well as the entire physics community about the fact that acceleration is not relative? You believe that acceleration is relative in the same way as velocity? That given a discrete energy input, the change in relative velocity for one object is the same as all other objects being moved instead? Or do you simply not believe in energy and forces at all? Do you believe that the resistance to a change in relative velocity (inertia) doesnt exist?
@@WizardsOfTheGhost No we are not disagreeing with Einstein; Einstein actually agreed with our position, and it was part of his inspiration for developing GR. Our argument regards the locally un-definability of inertial frames. One could potentially argue a consequence of this un-definability is that acceleration must be made relative in some manner. However, the typical argument is that something else lends inertial frames their objective character (this was Einstein's stance). Acceleration, in-and-of-itself, cannot be responsible, since its definition is purely mathematical/coordinative.
@@dialectphilosophy Inertial frames are definable and can be tested and observed. For acceleration to continue, a force needs to be continuously applied. Which is why if you were accelerating in a direction and let go of an object you were holding it would not continue to accelerate unless the force were also applied to it separate from you. Without force objects do not change between inertial frames. Its the exact reason gravity works. Gravity is literally just acceleration caused by the warping of spacetime.
@@WizardsOfTheGhost Huh, no... Gravity lets you experience relative acceleration without the absolute acceleration that's the topic here. It's only when you fall against a planet, that you're "accelerated" absolutely by the surface of the planet. And then you've ceased to accelerate relative to your coordinate system.
The very same kind of problem exists with mass actually, as you could always rescale it. In fact, in a world with only electric fields/interactions, there is no way to discriminate the (absolute) motions of similar q/m physical objects. This excess "freedom" should convince you that there is some kind of redundancy in these charges, or that there has to exist another fundamental interaction that would "split" those (as in, there should exist a physical experiment involving other interactions that are able to discriminate the motion of two similar q/m physical objects)
Dialect, you got it wrong! Force & Acceleration both exist and are independent of your feelings. And force does not cause acceleration only, instead it could just increase mass or energy of an object without accelerating it!
No, force and four-acceleration are merely assumed by the frameworks of the theories to exist absolutely. See our video "Newton vs. Mach" for further insight into this subject.
AFAIK when you ‘feel’ a force you are feeling compression or decompression. This happens to all objects that are not a single dimensionless point, so therefore all objects. Even in a gravity field some atoms of an object will be closer to the center than others and experience it slightly differently. Of course that would be hard to measure, but that isn’t the point. Our mathematical approximations can’t distinguish which element is moving, but that is only because it is an approximation using dimensionless points that don’t exist. I could be wrong, so I’m curious how compression/decompression fits into this idea. Perhaps you can’t tell which atom is causing the compression, or which proton for that matter, but isn’t the whole body feeling a force if it is compressing?
3:30 You talk about a train accelerating "smoothly enough so you don't notice it" but if I had an accelerometer (such as a 2 masses held together by a spring) that could measure to ARBITRARY PRECISION, then you'd always be able to tell whether you're the one accelerating or not, even if it's not noticable enough to feel with the limited human body. In other words, you can always tell whether your frame of reference is inertial or not. Acceleration is objective!
As discussed in "Newton vs. Mach" an accelerometer has to be calibrated beforehand in order to make any sense of its readings, and so does not measure absolute acceleration (which is an undefined and non-sensical concept) but rather acceleration relative to the frame of calibration.
@@dialectphilosophyand in inertial frame accelerometer will show the same result regardless of it's direction, you can simply rotate it and if the lenght of a spring is different along the specific direction it is an accelerated frame. Otherwise it is an inertial frame.
@@dialectphilosophy Can't we just measure acceleration by, say, throwing a ball or ejecting a bullet in a direction perpendicular to the supposed direction of acceleration, and then observe whether the projectile follows a straight path? If the object follows a straight path we know we are in an inertial frame, otherwise a curved path would indicate that we are accelerating!
Observing means interacting. You can't observe without receiving something (light,...). And if you receive something, you yourself must be an entity (object,...) within the system. In physics there's no such thing as a "neutral" observer.
Given the example of the twins in space with no reference. If one did accelerate away from the other, wouldn't they be able to deduce who is the one that accelerated? Let us assume that Alice accelerated away from Bob and both of them had a frictionless surface with a ball on it. Alice would see the ball move to the back of the plane whereas Bob would not. Given that there is no other information in the universe, then we can demonstrate that Alice is indeed accelerating and Bob is not. In the video, the explanation (5:00) would be that there is no way to tell if your refrence frame is accelerating because it can be due to some other mechanism that is moving it. Is it reasonable to state that there is no mechanism in this situation or would that count as measurement information?
Hey Mark, great questions! The issue with accelerometers here is that in order to associate a coordinate acceleration with a real acceleration, you first need to have an inertial frame. But once you take the twins out of the regular universe and put them in empty space, you lose any way to define an inertial frame. If you ascribe to Alice and Bob total knowledge of all the universe, and insert an accelerometer that distinguishes one of the twins' accelerations, then what you are asserting is that it is the addition of the accelerometer that is responsible for the definition of the inertial frame, and hence the breaking of the symmetry, which would in turn imply that your measurement tool somehow creates your reality.
@@dialectphilosophy I think it's resolved by the twins starting together, and one twin pushes something away from itself to accelerate. Whether they carry an accelerometer that is inaccurate or not doesn't matter, it's the twin that pushes something away that experienced more acceleration.
@@alexjohnward Exactly!! Yes, I've been trying to mention this on other videos of the twin paradox including one of Dialect's videos as well (I think anyway). This is a crucial piece they always leave out. The only way to accelerate is to exchange momentum with something else. This is literally in Newton's laws. You can compare your motion to the thing that you exchanged momentum with, whether that is something outside you interacted with (pushing an object) or ejecting a part of yourself (like a rocket).
I think one can tell if it is on an inertial frame of reference or not by checking homogeneity and isotropy of space and homogeneity of time, rather than in a "feel force" argument. I belive the first method is really clear and unambiguous and the fact that we see objects accelerate is a consequence of interaction. From and accelerating object due to interaction one can check that objects which don't interact (this may be where the argument may be weaker) break this frame of reference spacetime symmetry properties.
In "Spacetime Physics", Taylor and Wheeler define an inertial reference frame as follows: "A reference frame is said to be inertial in a certain region of space and time when, throughout that region of spacetime, and within some specified accuracy, every test particle that is initially at rest remains at rest, and every test particle that is initially in motion continues that motion without change in speed or in direction." According to this definition, inertial frames are always local ones. An accelerating elevator in free fall can be an inertial reference frame.
Acceleration is simply a change in your worldline vector. The change requires energy. The force we feel is nerve endings in the mass of our bodies sensing is moving from our initial state, sending signals to the brain. We can also see water in a bucket, or changes on an accelerometer.
Ok, maybe I'll look like an idiot here, but something is off in the thought experiment. When you're in a free fall, there is a spaghettification effect (your feet are slightly more attracted than your head) and thus, I can tell if there is a gravitational field around. I know that GR speculates that the "free falling object" is a size-less point. But then we cannot apply the reasoning of an apple (which has a size) and say it does not feel the acceleration. In the example of the passenger in a train, why does he feel the acceleration ? Because the train pushes the seat, then the seat pushes on the back of the passenger, etc. That's the equivalent of the spaghettification in acceleration. The reason why we don't feel like the passenger in a train when we are falling is because the gravity field is very smooth (almost continuously spread) and each part of the falling object is accelerating *almost* together at *almost* the same time. But that does not mean that there is not a theoretical/measurable difference.
Some people say the object "feels" a force (meaning that the force acts on the object) but they just say it as a figure of speech but it can be confusing because it sounds like the object is literally eperiencing a sensation, which isn't the case. If you're in the car and accelerating, you can feel an effect of the acceleration, which is that you get a bit squashed against the seat. That's not the force itself that you're sensing. It's a biproduct of the acceleration which is that you get a bit squashed.
Inertial means that a mass is giving a resistance against changing its movement away from what ever straight path thru spacetime it is taking at the moment. For example the accelerometer in our ears measures forces thru the liquid that wants to keep its initial movement and therefor is moving relative to our body if the body experiences a force. So you can actually feel a force working on your body.
Yes, acceleration is one potential result of a force, but it can be resisted by a counteracting static force due to molecular forces causing friction and strain in the mass. So force is measurable. Force will change the velocity of mass if it is no restrained by an opposing force so again you can measure it my measuring the force required to prevent a change in velocity of the mass.
This video is great and make a very compelling argument, but there is still one thing that confuse me. Let's say there is 2 boxes each with measuring instruments and one person inside in an otherwise empty universe, the boxes start next to one another with no speed relative to each other, then, the distance between the boxes start increasing faster and faster, let's say it increase like d(t) = t². In this situation as you point out, each of the boxes' passengers has an equal right to say that they are static while the other is accelerating or vice-versa, but! Let's now say that in one of the boxes, the passenger experience a constant push in the direction of the other box and the instruments on board read an "acceleration" a(t) = 2, meanwhile, in the other box, the passenger doesn't feel anything and the onboard instruments read 0. My question is, since acceleration is relative and each passenger has an equal right to claim that it is the other that is accelerating, where does the first box's passenger's experience and instrument's reading come from? How do we explain them? Does it have to do with space-time curvature?
Pure classic philosophy. Thought-inspiring, but for other purposes it feels quite useless. And I guess the same reasoning can be applied to any physics concept. (What is mass/time/distance “REALLY”?).
(7:55) I have always assumed that my grocer has a spring in his scale, so you can only imagine my astonishment when he used the theory of relativity to weight my tomatoes!
We speak of "feeling" a force because we have the acceleration detection machinery built in, so it is something everyone is aware of, but obviously the phenomenon exists absent any knowledge of it. But in the imagined room with suspended ball, the person in the room would also experience the acceleration in other ways than observing the ball. The idea that it's impossible to know if your observer frame is inertial by local tests, as opposed to observation of other objects, is false. There are many reliable "blind" tests for acceleration.
omg I was always so confused when my teacher said f = ma was determined "experimentally" and was like "if it's measured in kg.m/s² because of the formula, how would he know before coming up with it how to measure it anyways?"
This is a very interesting video, but I think you are missing one point. No object is really solid. All objects, even the most solid objects behave in a way like a spring. This means that when a force is applied to an object, it is usually not applied homogeneously on all its parts, but mostly on one part. So when a force is applied to an object, the acceleration is not applied instantly to all its parts, but applied first to one part, causing the object to shrink slightly. The shrinking increases the inner tension forces, which causes the rest of the object to accelerate at the same rate. Try imagining accelerating a spring by pushing it, and you will see what I mean. This shrinking is what activates your nerves, but you can technically measure it by other methods. You do not need the surroundings to know that a force is applied to you. In the example of the accelerometer in a closed room, you forgot that the person is going to feel a force due to the non-homogeneous acceleration applied to him. That is, his feet will accelerate before his head. Even if the non-homogeneous acceleration is too slight to detect by human senses, (like the example of the train) it is still measurable by more subtle devices. If you would apply the force homogeneously to all parts of the object, perhaps like with a charged body in an electric or magnetic field, theoretically you can create an accelerating frame of reference with real undetectable force.
You should be abke to still detect electrical forces by changing/transferring charge between the objects in your reference frame, which will cause force changes and acceleration changes in those objects. And for superficial charges, the force will be non homogeneous too.
If one imagines that to any single atom of your body is connected a infinitely thin and massles string and each string in turn is hooked, on the other edge, to an object that may accelerate, then your body will never experience the feeling of acceleration, because all atoms behave like a single object. That's in my opinion, how fields work.
From what I understand proper acceleration is simply a mechanical force applied on the object, it may not even have a coordinate component. Just stress on the mass. Say in the context of general relativity when a vessel accelerates just to stay in one position in an orbital free fall.
You can always deduce if you are in a accelerating train with a ball, if it was at rest and stays at rest it is not an accelerating train but if it doesn't stay at rest it is an accelerating train.
I love your video on the metric tensor so I arrived here. Quick side note: the fact that a force causes an acceleration is not metaphysics, that is physics as defined by Newton. 'Feel' is associated with the biological conception of sensation and perception. Biological organisms can 'feel' forces, but does an electron 'feel' the electromagnetic force from other charged objects? That is metaphysics. We know things 'experience' forces, thus things move.
We may miss the feeling of force when a train accelerates smoothly enough....because the acceleration is very small ...and we are often not paying too much attention to it. But that does not mean the feeling is not there. But great video....got me into thinking over the basics again.
Yeah but that feeling is caused by the seat’s matter hitting your body, and the effect it has on it is exactly the same it would have had if it was you who hit the seat. You still cannot discern whether it is you who is accelerating or the train.
If you were born free falling in a uniform gravitational field, and lived your life in free fall, and made free falling friends, you would never know that gravity exists and you would say you are inertial cause there are no forces acting on you. Your friends would also agree on the motion you describe for other objects, like kicking a ball (thus accelerating). This is what happens with our solar system. It is being accelerated uniformly by gravity coming from far away, and you BELIEVE it’s inertial because we all agree on accelerations outside the free fall. On the other hand if the gravitational field were not uniform, you would see other objects far from you accelerating and others would see those objects accelerating but you would disagree on the acceleration, because both observers are differently accelerated. A third person somewhere else would see you and the second person accelerating IN A DIFFERENT WAY that you and the second person see each other. Inertial frames may agree on accelerations, but accelerated people don’t. But no real inertial frame exists cause it’s impossible to tell if you are truly inertial. All the “accelerated” observers felt inertial in their frame of reference. The word “fictitious force” is what inertial observes named the forces they don’t perceive, implying that what they see is real, but an inertial frame can only be a local thing. For an inertial frame to be global you must have no interactions. There’s no such thing in the Universe. Summary: there is no global inertial frame only local. Those who agree on accelerations are just being accelerated in the same way, as if in a uniform gravity field. Those who don’t agree on accelerations are just being accelerated differently. In both cases, they are locally inertial, but the former insist they are globally inertial, just cause they have more people backing them up 😂
@@_Xeto We are indeed in a free fall under the Sun’s gravitational pull…. So we do not really feel Sun’s attractive force. It’s the hard crest of planet earth that does not let us freely sink to the centre of the Earth under earth’s gravitational pull … therefore we feel earth’s gravity.
Great video!! Continue doing them please. Just one question: if I am in a closed room and attach an accelerometer to the wall, that says 9.8m/S2, can I ensure that I am not in an inertial frame of reference?
That answer depends on your relative knowledge of the system; are you familiar with the accelerometer instrument, have you properly calibrated it prior in an inertial frame, can you guarantee that nothing else might be causing the accelerometer to move? etc.
@@dialectphilosophy ok, then assume - I am in our real universe - I calibrated it prior in an inertial frame( not necessary if i am using my laser beam method) - nothing else might be causing the accelerometer to move - the definition of inertial frame is just the same as in general relativity, where acceleration is still absolute.
Forces exist whether we feel them or not. Can you feel the magnetic lines of force acting on iron filings around a magnet or on a compass needle? Nevertheless, the force is empirically evident. No feelings required.
2:46 I feel like this part needs to be elaborated more because it was confusing to me. To my understanding, you need force in order to measure inertial mass and passive gravitational mass (fictitious force for the latter perhaps). I can see that force is not needed for active gravitational mass, and if we can treat active gravitational mass and inertial mass as equivalents (because there's no evidence of deviation so far), then that part made sense. Though, I'm still unsure if that's what you were arguing.
There are some serious flaws and your reasoning here. 1. Not feeling the acceleration when is a vehicle that starts up slowly and smoothly it's simply a result of the acceleration being too small for you to feel. That is it is simply too small to be detected by our senses. That does not mean that the acceleration and the force or not absolute, just if they are too small for you to notice. 2. Your illustration of the accelerometer in a room that most likely is not accelerating is not a problem with being able to measure an actual acceleration, both of the possible causes that you gave are a result of someone applying a force to the pendulum. Hence the problem is, that you do not have it honest accelerometer, the one that has been rigged by someone deliberately trying to trick you. The fundamental flaw in your argument is the simple fact that acceleration is locally measurable. For example, the Earth's rotation can be measured with an interferometer that sends light in two opposite directions, if it is big enough. Basically what you were doing in this video is, relying on an acceleration that is below perceptibility, and someone trying to trick you by applying a force to the pendulum. Neither of these, actually indicates that acceleration is not absolute. However, the fact that we can feel it when acceleration is high enough, and the fact that acceleration can be measured, when the device is functioning properly, shows that acceleration can be locally measured without any reference to the outside universe.
Being pushed into the seat is not the feeling of your acceleration - rather, it's the feeling of the car's acceleration! If you were made of metal, and both you, and the car were accelerated by a magnet, you would not feel anything at all!
The train example that you give is floored. It just shows the fallible human sensors are. If you asked a accelerometer what was happening it would tell you.
Deduction of local orders of Kinematics means we assume our notion of space, velocity, acceleration etc have temporal-orders of 0,1,2,3,... Yet this is a local assumption. Imagine an observer that deduces what we observe as velocity (first-order) they observe as spacial coordinate (null-order). Would relativity be relative to this shift in order???
A single particle doesn't "feel" force, but multiparticle systems do. Same with entropy. It's an interesting perspective, but it seems to show we don't fully understand the physical world. Our best theories are know to be wrong, good mathematical models for our context, but still wrong.
I am struggling to see the issue with thinking of acceleration as absolute. I don't think relative comparisons really need to come into it. It is a concept that stands on its own. You can add another object to your thought experiment if you like, and then see the implication for relative motion/position but it seems entirely optional and unnecessary for having a conception of acceleration. In my understanding acceleration is fundamental to the definition of mass. I define mass as energy that resists acceleration. Anything with mass, even the most fundamental things, are composite entities that involve interactions between parts such as the Higs field or the quarks and gluons in hadrons. Without such interactions, the unencumbered energy would travel at c and have no mass. In the photon box analogy, there is a pressure on the back side of the box when a force accelerates the object, which could just as well be a neutron, a quark, a person or a cheese burger. In all cases where there is mass there is something confining energy, preventing it from traveling at c creating an asymmetry in pressure when it is accelerated that resists said acceleration. I could be wrong but I have listened to your arguments multiple times and I have failed to be convinced that we need to think of acceleration as a purely relative phenomenon.
These videos are great. My only question is when you say 'force', do you just mean gravitational force? As you reference General Relativity. Or do you mean ALL forces? For example, are you claiming that the Electro-Magnetic Force is a curvature in some Electro-Magnetic Field? Strong/Weak Nuclear forces, are curvatures in Strong/Weak Nuclear Fields? I'm just trying to wrap my head around the property of charge.
This video is regarding the classical definition of "force" as described by _Newtonian_ mechanics and the _Lorentz_ force for electrodynamics, so all contact and inertia (pseudo/fictional) forces on bodies with inertial and gravitational mass. The classical force was created with calculus and differential equation to determine causality, the action, change in momentum, and the path of point mass that deviates from a straight world line and being accelerated by a force. The video briefly mentions that in Quantum Field Theory, the concept of a "force" has been abandoned. The classical field theory of electromagnetism, _Special_ relativity, and _General_ relativity can be approximated using forces and field theory. The fundamental interactions and elementary particles (except gravity) are described as "excitations in quantum fields," rather than "curvature." Spacetime curvature versus flatness is something different.
None of this makes sense if we consider gravity a force. Gravity can't be a force, because for us someone freely falling due to gravity doesn't experience absolute acceleration. Only the relative kind. Absolute acceleration is what is responsible for time dilation.
idk what about a *roller coaster?* like yeah i know that i am in it an can see stuff moving around me going faster, but I can feel being pushed into the back of my seat as it speeds up, or being pulled out of it from the centrifugal force when it spins.
Profound stuff - sure to piss off the Star Wars fans! But seriously, you’re onto something here. Make some more videos, soon. All the best. A fellow astute thinker. 😊
p.s. you can't directly measure velocity, energy etc. either. Physics is bootstrapping and we could "easily" replace it with others, whilst not having the foggiest about what's "really" going on. There is no escape from this
when you think about it, the only thing we ever really measure is distance and how it changes. Time? A clock has something that moves a certain distance at a regular time interval. Velocity? We measure the change in distance per unit time. Acceleration? We measure the change in velocity per unit time. Mass? A scale measures the distance a spring is compressed.
Wouldn't this make gravity and acceleration the same? Since gravity is the amount of energy which creates the force and accelerating is adding energy to move an object therefore making it the same as gravity but with a different kind of energy?
With any rotation isn't it plausible to know you're in an non inertial frame of reference, since distant objects appear to be moving faster than light? I agree with what you've said in the video, just confused with rotating reference frames.
Hey, thanks for watching! In GR, the speed of light is only constant locally; so in more global frames objects can move faster than the speed of light. This would likely indeed indicate a rotating or non-inertial reference frame. In this video here we suggest the possibility that force could be relative on a local scale, but on more global scales force is easily discerned through these sorts of fashions.
@@dialectphilosophy In which "global frames" can an object move faster than the speed of light? We are in a universe. in that universe, the speed limit is the speed of light (although it's actually the speed of causality ), PERIOD! BUT, we are in a expanding spacetime, so teorectically we would be moving at a speed higher than the speed of light. But it would be like an ant moving in a piece of elastic fabric. If the speed of the ant would be its speed plus the speed in which the fabric is expanding. You said "the speed of light is only constant locally". That is not true. Speed of light is the speed of causality and has the same value, unless it changes the medium, in this case, the photons interact with the new medium and it looks as if the speed is less than in vacuum, but this is well explained by Maxwell equations.
@@ranyeredt "Speed of light is the speed of causality" - Wrong. You can believe that philosophically, but the science does not show that. Science deals with observables only. It does not support claims about causation. Science is built upon reproducibility. It is built upon peer review. It is always up for adjustments when new theories are devised that provide better explanations than current ones. As such, it can not support claims about causation. "we are in a expanding spacetime" - in other words "I have bought into everything mainstream physics education tells me to think, regardless of how ridiculous it is". Inflationary cosmology is just a theory. It is still disputed somewhat. It is not absolute. Modern education is seriously lacking when it comes to teaching philosophy, logic, and skepticism.
Yeah, because they are not accelerating by the GR rules. They seem to acceletate in a non-inertial ref frame of a planet they are falling to, however we do not care about Non-inertial frames, you can say the Universe revolves around you while you are rotating, it does not mean anything. That is why gravity is a false force in GR, like Coriolis force: they are forces only in non-inertial frames.
From the beginning I was skeptical that if velocities are relative so should be acceleration. So am I feeling the force or the reference frame. is force even real?
"feeling" and "seeing" aside, surely by one pressing the throttle pedal you know you are mechanically applying "force" and causing accelerating and the other who is doing nothing is not given all else equal ... how would one translate this to absolute acceleration? ...
The "co moving" reference frame in which the CMB is the same temp in all directions really seems like a universal reference frame. Even though it's not. But, if you wanted to compare a point in space with literally everything else, it's about as good as it gets. Im probably wrong.😊
8:49 "We have no knowledge of profound causes of force" What makes you think that? Force is a name given to two or many physical and observable quantities it seems Curious to know your perspective!
F=ma. Force equals Acceleration. Acceleration creates Acceleration. The universe is a series of chain reactions. A perpetual motion machine. What we don't know, and possibly never will. Is what the initial acceleration event was. F=ma describes an infinite, unbounded universe. Everything and yet nothing at all. The God 'said' Let there be light. God was what started the chain reaction. Changed F=ma to E=mc a finite universe bounded by the speed of light. E=mc. Acceleration creates distance. Distance is length. Length is an attribute of space/mass. Acceleration creates space. Creates time. Creates the universe. Defines the universe. The 64,000 dollar question is, who are what triggered the initial acceleration event?
@@stewiesaidthat i think you understand nothing about F=ma because creator said i will stop the universe when i will find no people doing good so who are you to say that the universe is not infinitely finite? Because creator creates infinity and that infinity is also finite for him because he creates that. Creator is above everything so stop being stupid and don't start to lump religion with science because true religion is the word of creator so to understand it we need more knowledge and science is just a part of that knowledge nothing more than that which always changes and somethings will never change as they are truth and force is empirical truth so earn knowledge and study how to be a good philosopher not a bad one because knowledge is all. Moreover, general relativity never showed force doesn't exist rsther it showed force can exist in geometric shapes. Only misleading science persons who don't understand math equations will say that general relativity denies force. Man we really do live in a universe that is full of misleading people now. Do you even know anything about electro magnetic permittivity and nasa even found electro magnetic permittivity in space which is empirical.
@@ourfamily.zsl5 What’s the name of your religious view? It’s interesting to learn other perspectives, but when you claim to be 100% right, and everyone else is 100% wrong, you won’t persuade anyone. The world has many religions and sub-religions. On a scientific channel, I think it’s best to limit to scientific evidence and not involve religion. You can create religious videos to speak from another perspective.
@@ian-flanagan Bro so lame. Haven't you read about the comment i have replied? I was showing him another one tone told by religion so handling science with religion is the problem. Religion is the word of the creator and you don't know how you will prove them until science shows some empirical evidence. I wa never showing you i am correct. O just showed you what logic and math is saying. Lame and you start talking about being adamant but it is you who is a big fan of your own words.
When reading about General Relativity, one claim I encountered frequently was the justification for gravity not being a force. It goes like this: Imagine you are in freefall. You won't feel a force acting on you, even though you're being accelerated by gravity. On the other hand, if you're in a car that's accelerating, you will feel it. Therefore, gravity is not a force but a warping of spacetime. Took me a long time to see that this is nonsense.
Yeah it's good point to raise; "force" is defined empirically via being able to measure weight or see deviations of free bodies, etc. All those definitions fail for gravity, which is why we have to say we're accelerating "up" at the surface of the earth. The alternative of course is to recognize that acceleration is relative and we just need to identify what we're accelerating relative to.
Force should be the first derivative of momentum, not simply acceleration, which does have an observable component namely it's conservation. This is to say inertia, or mass, itself. Inertia is the thing we 'feel' as we accelerate. For example when a proton colides with an object the majority of its mass is do to the internal 'collisions' of its quarks or rather to the exchange of gluons , creation and annellation of quarks and so on. Exactly the strong force. Also, for now most scientist assume gravity will be added to quantum mechanics not that strong, weak, and electromagnetic forces will be shown as illusory.
Defining force as the derivative of momentum is certainly no issues; but unfortunately it hardly resolves the problem. The conservation of momentum is a direct consequence of an inertial frame (i.e., in a non-inertial frame, momentum will not be conserved) so the definition only works so long as one is certain one's frame is inertial. To be certain one's frame is inertial means they have to be certain it is not accelerating... meaning they have to be certain the derivative of momentum is conserved... meaning they have to be certain their frame is inertial (repeat vicious cycle indefinitely...)
Summary 1: This simply means REAL ACCELERATIONs (not pseudo accelerations) ARE NOT COORDINATIVE AND HENCE THEY ARE NOT RELATIVE. This is because they can be detected from within the reference frame by performing simple experiments. However, constant speeds (including v = 0) is very much relative. That is, constant speed can't be detected without referring to the "outside" world.
If something breaks due to internal stress during acceleration in a rocket ship, an observer in the ship would not necessarily be able to explain it. We can't assume a frame of reference to have any knowledge, only to be able to observe motion. To a "dumb" observer on the ship, the fracture would be spontaneous and spooky. To an "intelligent" observer the fracture is explained by an increase in internal stress, a concept invented by man. Therefore, concepts such as force and stress are relative, observer-dependent concepts and can't be real, objective truths about nature. I THINK that is is the point Dialect is making.
You cannot directly measure Time either. What you measure is a constant velocity over a constant distance. This is true with a classic clock whose hand moves around a circle off a given size at a constant velocity. This is also true with more sophisticated clocks, but the distance is a wave-length and the velocity is C.
You also cannot measure velocity absolutely. Instead you must compare distances traversed between two objects up to a "present moment" to determine a relative speed betweeen them.
I did not quite get why the accelerometer does not solve this? In another video you mention that it must be calibrated relative to something, which is true. But this is why we rely on fundamental constants to calibrate our SI base units to and assume these quantities stay constant as time progresses. Physics has to be useful for predicting outcomes of experiments, enabling technologies. It is not concerned with the "true" nature of reality as long as it is not measurable. For all we know we could as well just be a boltzmann brain. Philosophy is an interesting field in and of itself, concerned with questions like "the ship of theseus" and the like. It has been helpful to physics and technology by posing new questions to ask. But you'll have to remind yourself that physics is mostly just concerned with frameworks for technologically useful predictions, everything else is "extra". As Descartes once said "I think therefore I am" we have to make reasonable assumptions from which we can build our frameworks upon. There has to be some sort of value proposition to change views, albeit just an exploration out of curiosity.
When we measure systems to validate or develop theories of motion relevant to macroscopic objects do we ever involve anything other than electromagnetic forces now that we treat gravity as a curvature of space time? If not then is a relevant force just a deviation from some kind of electromagnetic equilibrium? Then is a frame shift actually a change in things like spin vector distribution but maybe other properties that add up to the appearance of special relativity?
In terms of observable linear momentum (assuming you're okay with that since mass is lumped in), can the video be summed up as the following statement? You can observe supplies but you can't know sources.
Acceleration is impossible without Force. But Force is not impossible without acceleration. A static compressed spring held in your hand can give you the experience of force without any acceleration. Please talk about the distinction between Internal and External forces in your video when you invoke the concept of Feeling Force.
Hey Dialect, I'm confused with this! Consider a man in rotation where he has nothing in the universe for relating with (you know!). Then according to him, he is still. But if his arms are lifted up, we could understand that the man is in rotation. Doesn't it mean that there is something that can be said relative to even in the nothingness (maybe the space itself!). What I mean is among all the possibilities, the man's arms are not lifted in only one scenario. And that is the case in which he is still (not rotating). So does the non-lifted arms mean that he is at rest relative to something eventhough we couldn't find any differences between any of the scenarios with our HUMAN PERCEPTIONS?
That's a great question -- it goes to the heart of Newton's Bucket Experiment / Mach's principle. When Einstein considered it, he felt that the lifting of the arms, if considered under Newtonian mechanics, could only be explained by adopting a "privileged space". But since such a space was not observable, he rejected the possibility of it and concluded that the cause for the lifting of the arms must lie outside the system. So to summarize, in the Einstein view, if the person's arms are lifting, then there MUST be something observable beyond them which they are rotating with respect to. A person in empty space could never rotate to begin with. As to the point you make about human perceptions, if you are asserting that there might be some hidden variable that is not measurable but which exists and which distinguishes local rotation from non-rotation, that is an interesting idea perhaps, but it might prove tricky building an empirical theory around.
@@dialectphilosophy Thank you very much, Dialect! Let me get some knowledge of what you've said above, as I have no idea about what is 'privileged space' or whatsoever. And a quick suggestion, if you add something behind your channel name, like 'Dialect - Exploring Science', that would be easy for your subscribers to search for your channel and that helps your channel to stand out among those creepy 'Language Dialect' channels, at least until you grow up(like VSauce!). And that's totally your wish, that's just a suggestion! Thank you very much!
You don't feel the force, you feel the collision of your matter on the seat. When you accelerate what you feel is your internal organs and tissues colliding and pushing each other as a result of different acceleration throughout your body, which is a macro system, because the force isn't being applied uniformly across your whole body. If the force were to be applied on all your molecules and atoms uniformly you wouldn't feel it, in fact you would think the whole universe just started accelerating in the opposite direction.
You've come up with lots of reasons why the question of acceleration can be problematic. To go from that and say it's RELATIVE is specious. An electrically neutral ball in a non-accelerating spacecraft floats freely. Then the engine is switched on and the ball is forced against the bulkhead in the direction of the engine and opposite the direction of acceleration. That is force and acceleration, absolutely, pure and simple. Feeling and coordinates have nothing to do with it.
All acceleration is defined relationally, meaning you cannot speak of acceleration without implying what you are accelerating relative to. The issue is not that acceleration is relative (since you cannot define it any other way) but why it acquires such a seemingly objective role in our empirical reality. According to your engine's perspective, it might as well have been the ball which accelerated. The use of an accelerometer ultimately tells you nothing unless you inject certain a priori assumptions into your scenario, as we discuss in the video.
@@dialectphilosophy But acceleration is felt inside a ship not because you infer or deduce that you are the one that is moving, changing speed, accelerating, but because your mass is resisting change in speed (because of inertia) and your body is therefore pushed back into the seat. You are claiming, if I understand correctly, that acceleration is applied universally. But that's never the case. I feel your arguments always presupposes ideal point-like object. Also, your train example is misleading. You don't confuse the motion because you don't feel acceleration, but because the acceleration is just so weak. If you would accelerate with the force of 9 Gs, there won't be any confusion. And your fainting would prove that. (Again, even human body is not a point-like object.) On the other hand, I like your thesis that force is mathematical abstraction. In the same way that energy is also mathematical abstraction, only defined as ability for something to do work. But after that your argument is flawed. Even if everything that is not empirical (that we are not able to measure it directly, whatever that means), is really an abstraction (here I am talking about force, energy, practically all physics), that does not mean these concepts aren't always referring back, through math, to the measurable phenomena. Force is always referring back to acceleration and mass.
@@petpaltea but who is to say that you are the one accellerating forward, and not the atoms in your body accellerating backwards and the spacecraft standing still? you can't know, without knowing that the engine is on and pushing the entire craft forward. if you are driving in a car at 60mph, and you put your hand out the window, who is to say that it is not the air moving into your hand, instead of your hand moving into the air. who is to say it is you moving through space, and not space moving through you?
@@dialectphilosophy Ok, maybe I'll look like an idiot here, but something is off in the thought experiment. When you're in a free fall, there is a spaghettification effect (your feet are slightly more attracted than your head) and thus, I can tell if there is a gravitational field around. I know that GR speculates that the "free falling object" is a size-less point. But then we cannot apply the reasoning of an apple (which has a size) and say it does not feel the acceleration. In the example of the passenger in a train, why does he feel the acceleration ? Because the train pushes the seat, then the seat pushes on the back of the passenger, etc. That's the equivalent of the spaghettification in acceleration. The reason why we don't feel like the passenger in a train when we are falling is because the gravity field is very smooth (almost continuously spread) and each part of the falling object is accelerating *almost* together at *almost* the same time. But that does not mean that there is not a theoretical/measurable difference.
Acceleration of the ball is felt simply because force applied to it is not uniformly spead. The outer of the ball touches the bulkhead, and the rest tries to resist the force thus is felt. That's why they say gravity is not a force because its so equally spread that is applied uniformly in all areas thus not "felt" while it is still a force. I hope i make sense. If in some magical way u could do the same for electric force (a negative source attracting a positive force) it would be the same. Of course electrical force acts in closer distances, thus one side of a ball would receive more force than the other side, but in gravity is we could discern this miniscule difference it would be exactly the same.
What about changing acceleration or accelerating changing acceleration? More philosophy…-ve speed or going slower than stopped. Accelerating into the stopped state. Figure it out!!!
A better question is that can you design a device that can detect if the current reference frame is accelerating or not and thus inertial or not, that way you can frame this video better than asking the question of whether we feel the acceleration of the frame of reference or not. The example with a pendulum inside an isolated room and the person deducing that there is a magnet behind the wall instead of deducing that the whole room is accelerating does not make a little bit of sense, I think you lost what you were trying to convey there as it is entirely possible to deduce from that event that the whole room is accelerating...
Please correct me. Inertial and non inertial frame is distinguished through pseudo forces irrespective of knowledge about the surroundings. And pseudo forces is "observed at most qualitatively", and this pseudo forces is stated in "experimental" !st law of Newton.
We are never in an inertial frame, so nothing can be really calibrated by men. But we are in a almost inertial frame and can well feel forces, in my opinion. Likewise, we can use an accelerometer and calibrate it up to a certain extent by using all 3 directions of space. And then we can measure accelerations with an error that is neglectable. Why would such a small error make such a big difference leading to the statement that we cannot feel force?
You could calibrate your accelerometer in as many directions as you like, but you could never guarantee that you weren't accelerating in those direction during the calibration process, so at best you could only obtain to probabilistic likelihood of experiencing force. (Plus, if you want proof that the human body itself cannot differentiate true from apparent motion, go to a planetarium or one of those Disney park rides where the screen moves around you, and see how your mind reacts...)
I agree that we can easily be fooled by our eyes because we never really are attentive to the usually small external accelerations of our body. Also we are constantly accelerating our body or parts of it ourselves by moving around or playing tennis so that this is kind of natural to us. The steady massive external acceleration upwards we perceive as weight because it‘s so constant. But ask Louis Hamilton if he feels the force when he starts a race.
When freely falling towards earth you experience an acceleration as observed by a observer on earth. Yet you feel nothing as gravity acts on each atom of your body the same. The acceleration felt in a train that is set into motion is only felt due to it acting on only some parts of your body that are in contact with the train, resulting in a force differential that can be felt by your Proprioception. Now lets say the whole universe started to accelerate in some direction. That is your very most basic inertial reference frame is accelerating from you, would you be able to tell it does?
So what about stress vs strain relationships in materials? Take steel for instance, we know it starts to yield at about 275 MPa, and this has been measured and tested in labs across the world. So why do these materials behave so predictably with regards to feeling a force if its such a mysterious phenomena?
If you apply a 275 MPa force to an entire piece of steel that is free of all other external forces, then it will simply accelerate the entire piece of steel, and the steel will not bend. This is the kind of “force” he’s talking about in the video. You’re talking about fixing a piece of steel to a large mass, and applying a force to a part of the steel body that is not fixed, which is really a different situation.
@@mensaswede4028 well if that's the case then the object will be subject to axial stress. If it's not evenly supported than it will also bending moments and even shear stresses as well. Either way, if the steel object is being accelerated then it's going to experience stress of some kind.
If your accelerometer is faulty, you will have faulty understandings... if the accelerometer is accurate, you will determine that the room is undergoing acceleration, even if you think it implausible.
Great video. One of the few that tries to be rigorously logical. What I am confused about is compression and tidal forces. If someone if punched the area where there are punched becomes compressed. If I can tell where a force is applied doesn't that me a force was applied? In the same way one's back is compressed when a train accelerates forward..
To address your compression question: consider matter with two states, compressed and uncompressed, as measured relative to some standard. Now, the question becomes, is the compressed state the inertial rest state, or is the un-compressed state the inertial rest state? The only way to really know the difference is for there to have been measurements already made of the material's natural compression state in a frame known to be inertial. Thus you couldn't ultimately use something like compression to define what a non-inertial force is.
@@dialectphilosophy Thank you for addressing my question. You video is a real break through. I still do not think you answered my question. "The only way to really know the difference is for there to have been measurements already made of the material's natural compression state in a frame known to be inertial." Why can't I measure the service area of the object. Why can't I know if the surface area deformed? The point is. "The only way to really know the difference is for there to have been measurements already made of the material's natural compression state in a frame known to be inertial." We must have measurements of some kind or were couldn't identify the object or know that I exists. If you are talking about an unknown object or an unknowable object then your point becomes meaningless. They is something you aren't saying or some assumption that you have that I do not.
@@TomTom-rh5gk You’re probably overthinking it just a little. You certainly can make measurements of surface area, compression or whatever else you’d like. But those measurements would just be meaningless numbers if you don’t have an inertial reference system to compare them to.
@@dialectphilosophy No, I am under thinking it . There is something you haven't explained. You say, "But those measurements would just be meaningless numbers if you don’t have an inertial reference system to compare them to." 1. Inertia is the inertial reference system. Inertia is the most basic property of an object. Without inertia, you do not have an object. 2. Without inertia an object changes for no reason because It lacks identity. 3. Without inertia you have nothing. You can’t even say that something accelerated because there is no something. .. I think your explanation is missing something. Everything you said made so much sense that you must have a hidden assumption that you need to express in words.
Now I can see why I never really "got" concepts like force, but rather memorized the treatment, and pretended to be comfortable with it, as presumably the teacher was also doing. The unsatisfactory feeling that the science was somehow settled and accepted, but I couldn't understand it, is maybe why I pursued mathematics, instead of physics. I'll make sure to teach my kids that it's ok (and desirable) to admit a lack of understanding, even on the most basic and common concepts.
Very well said!
@dialectphilosophy
One question: are you a philosopher? What you do is awesome.
This guy, dialect, is very misleading. Force is a fundamental property and to understand force, you need to understand what is wave because if you really want to understand force you need to understand how action was invented. And if you can understand all of these then you will be able to grasp quantum mechanics and that will lead you to force and then you will understand action is force. This guy creates a loop hole by not telling you the full story. I would advise you to tell your children to earn more knowledge and not to become happy by not being able to determine Truth and false. Even math uses zfc that states that numbers are empirical not something that was given to you from heavens. Thus these kind of channels are cheap philosophy that keeps hiding the evidence from you and tries to say wow that's cool. Henry Poincare was an intuitionist mathematician which is very bad. To be a good philosopher you need to be a skeptic, a logician and then an intuitionist, if i say wow the sea is a projection of earth's sky and show some evidence that supports my line. Will you start believing me? If you do then sad. But a sensible person will try to find counter evidence and if he finds that then that means either i am wrong or i was not being dishonest rather a biased person. That's what is happening sadly with these kinds of channels. When we talk about F=ma we mean if F exists only then m and a exists and if a exists only then m and F exists and if m exists only then F and a exists. So all of them are required for everyone's existence and general relativity never showed force doesn't exist rather it showed force exists in a different kind, like geometry okay. I guess i was clear enough.
@@dialectphilosophy stop giving cheap advice man. Rather read what i am saying, This guy, dialect, is very misleading. Force is a fundamental property and to understand force, you need to understand what is wave because if you really want to understand force you need to understand how action was invented. And if you can understand all of these then you will be able to grasp quantum mechanics and that will lead you to force and then you will understand action is force. This guy creates a loop hole by not telling you the full story. I would advise you to tell your children to earn more knowledge and not to become happy by not being able to determine Truth and false. Even math uses zfc that states that numbers are empirical not something that was given to you from heavens. Thus these kind of channels are cheap philosophy that keeps hiding the evidence from you and tries to say wow that's cool. Henry Poincare was an intuitionist mathematician which is very bad. To be a good philosopher you need to be a skeptic, a logician and then an intuitionist, if i say wow the sea is a projection of earth's sky and show some evidence that supports my line. Will you start believing me? If you do then sad. But a sensible person will try to find counter evidence and if he finds that then that means either i am wrong or i was not being dishonest rather a biased person. That's what is happening sadly with these kinds of channels. When we talk about F=ma we mean if F exists only then m and a exists and if a exists only then m and F exists and if m exists only then F and a exists. So all of them are required for everyone's existence and general relativity never showed force doesn't exist rather it showed force exists in a different kind, like geometry okay. I guess i was clear enough.
just like riding a bike
I have not even started watching the video, but I am going to give you a like because of the mere fact that you chose to do a video on such a seemingly basic and simple concept. Topics like these are usually hand-waved away by teachers and professors alike as if they don't warrant a deeper explanation and have already been logically figured out by minds greater than our own. As someone who has always felt dumb for questioning the most basic of concepts, especially in physics, it is very refreshing to see that you have made explainers on these topics and taken them with enough sincerity in an attempt to properly formalise the most fundamental notions
Feel force, feel time, feel space? If you delve on that, you can doubt everything, not just forces. Stay simple. With clocks we measure time intervals. With rules we measure space distances. With springs we measure force differences. In F=ma, we can use clocks and rules to evaluate the acceleration, a spring to evaluate the force, and the thing we really need to assume to exist beyond our measurement instruments is mass.
But you didn’t understand what the video was talking about. Force, unlike the rest of the above, is introduced not as an independent physical quantity, but as the product of acceleration and mass. By the way with spring you can only measure spacial displacement of this spring
@@noavailablenamesatall My body is build using electromagnetic interactions. With these I am endowed with senses that can see, hear, smell, taste, and touch. When you shake my hand, my body feels the pressure. I can also watch accelerations. In F=ma the only thing that I cannot see, hear, smell, taste or touch is mass. That's what I need to assume.
@@josecastro4465 You can see and touch a mass; when you see, touch, weight a mass you are measuring it, the same is for the Force. If you see a video of an accelerometer that is changing somehow you cannot know what is happening unless you have some "context" knowledge. At 5:05 it could also be that the entire room is rotating and you, that are watching the video, will not be able to see it. I will add that a ruler is a "reference frame" relative to which we are comparing lengths of objects. A notch of a ruler is the reference frame relative to which we measure the ruler...
@@josecastro4465 The video demonstrates the relativity of phenomena such as force and acceleration, which are postulated as absolute. You will always feel a relative difference in force depending on how your sensory system is calibrated
@@noavailablenamesatall in practical terms then relative is all the matters. Having played football for many years, believe there’s a tremendous amount of force on the field lol.
What's funny about the subject of inertial vs non-inertial reference frames is that there are apparently no inertial frames anywhere in the universe.
Inside the closed room the person is standing and the accelerometer is hanging from the ceiling. That can mean atleast two things:
1. There is a force that is pointing downwards.
2. The person and the ball are arranged inside the room in such a way in free space free from any external force.( let us assume that the only matter left in the universe is the concrete room with the things inside it)
In both the situation direction of acceleration can be observed.
Situation 1. The person may fall if the acceleration is high enough.
Situation 2. In case of an acceleration, the person will move towards a wall if the shoes he's wearing aren't fixed to the floor. If the shoes he is wearing are fixed to the floor , he will rotate and bang his head on a wall or floor.
Having watched the entire video, I think your point is just: "Force and acceleration cannot be defined without outside information."
But we can define: "If light always travels in a straight line in this frame of reference, then the frame of reference is inertial."
There is nothing wrong with this definition. If anyone has a different thought, rebuttals are welcome.
If you are on a spaceship falling towards earth via gravity, you are in free fall and a light beam would travel in a straight line in your reference frame. Yet for an observer on earth you are accelerating.
@@dragoscoco2173 No, because the effects of gravity, the observer on earth will see both the light on earth and the light in spaceship curved. The observer in spaceship won't see any of the light curve because their acceleration and gravity cancel out.
The observer on earth accelerated. not the spaceship.
@@babbrian7033 The spaceship accelerates in the ground reference frame, just as much as the Earth is accelerating in the spaceship reference frame.
@@dragoscoco2173 But because of gravity, the space flow towards the center of the earth. So the observer on earth must accelerate to stay stationary relative to the earth.
I think that means the earth observer have "real" acceleration. (Thay do observes light turning. By general relativity, gravity and acceleration are the same.)
@@babbrian7033 There are some problems though. "because of gravity, the space flow towards the center of the earth" that is just a visualization of an unknown process. Also remember that the spaceship has it's own gravity and pulls the Earth towards it too, complicating the matter.
I am more in the Forces are real camp, but find that gravity acting on every atom, means that it will be hard to impossible to tell if you experience it unless you view your surroundings. Acceleration acts only on the parts that pull or push you creating pressure that can be felt. They are the same but one is more evenly spread.
Some broad thoughts im thinking right now:
say,
1.) Force concerns how mass/matter reacts to motion.
2.) Matter/mass units can't (in essence) occupy the exact same space. So if you have multiple mass units, they are a distance apart from eachother.
3.) Max speed is C, so it will always take time to move mass across space.
So you have a blob of mass spread across space, another mass comes in contact with the blob (there must be motion involved). They can't occupy the same space. 'internal pressure' of a mass or w/e will be in an equilibrium if outside conditions stay the same. Now after the collision, at the point of contact theres a bunch of back and forth of pressure-waves I guess.. It takes time for pressure to spread acros the blob of mass. This squeezing and stretching of the volume units of mass, because of localised pressure changes inside of the blob, are what they mean by 'feeling force'.
If you happen to read this and think im an idiot its entirely possible. Got no real physics/math background. Would like to know why this would be wrong so I can see where i'm thinking wrong.
"Pressure" is defined as force per unit of surface. So, we do not really extend our intuition here by adding pressure to the equation. It's still about the nature of force, defined as the product of mass and its acceleration, i.e., its change of momentum, which we call its impulse. The problem is that we need to presume an inertial frame of reference to be able to define the background at which this acceleration can be observed.
This also applies to light. We say that light in a vacuum travels at its maximum speed. But that is under the condition of a local frame, where space-time is considered to be undisturbed. Over larger distances, the speed of light does not necessarily equal 'c', the well-known value that we normally mention as the speed of light.
3:06 Mass is not directly observable either. Mass can only defined with respect to an inertial frame.
This is easy to fix in Newtonian physics because accelerations are invariant under Galelian transformations.
The fix in relativity is more difficult, and leads directly to E=mc^2.
Time is not observable either - clocks can only be measured as a set of discrete events or deduced from distances.
Summary 3:
To find out inertial vs non-inertial frames NO REFERNCE TO ANYTHING OUTSIDE THE FRAME IS NECESSARY. Experiments confined within the frame are good enough to tell us if we are in an inertial frame or a non-inertial frame.
Finally, at this moment, my spring have been awakened. It feels the force.
Seriously "Force" does not have be felt. One of the easiest way to "observe" the force is the use of spring as a measure. In my humble opinion, spring does not "feel" anything. It does not have any knowledge about "inertial-ness". It also doesn't observe an acceleration, too. It's just a thing. It's different from me and my cat. But it perfectly & precisely react to the Force. How do you explain this?
Quantum mechanics doesn't even bother the force!!??? man, quantum world is FULL of forces. It even tells how different kind of forces are transmitted through the particles. It doesn't covers Einstein's gravity yet but gravity is actually included in the theory as graviton (undiscovered yet, though).
Okay, if you think, acceleration is caused by the "transformation of reference frame" you says, what about the "force" caused by the magnetic fields? how it's related to the "reference frame"? there is no acceleration but electron moves!
I really liked your clam on "twin paradox" (at least half of it) but this is total nonsense. I agree that there are lots of interpretation of the laws of the physics as long as it consistent with the theory. But if you want to make your point, you should explain why your interpretation is better than the others. For example, Everett introduce his new interpretation for quantum mechanics to eliminate Von Neumann's projection. Because as long as we have it, we can't apply quantum theory to the universe itself where there is no "outside". He did not say, there are thousand of universe correspond to every quantum state...he said this is the reasonable assumption to improve the theory. So what is the point of your interpretation...no offence but seriously you need more research on the topic your interested in!!!
Finally, this is the last claim. The reality of the variable in the physics law is actually questionable. In other words, the force may not be the "real thing". It only appears in the theory to clarify the relationship of the variable, that's all. But one thing for sure is, as I stated at the first of this comment, you can measure it actually. Therefore, I think it exists. But this is not a physics, it totally unrelated to the actual theory. It's more like philosophy than the physics.
An accelerometer such as a spring doesn't resolve the issue of how to measure force, because you are only still measuring something accelerating. As this video discussed, such a measurement has to be paired with additional information not intrinsic to the system in order for the conclusion to be made that a force is present. We discuss this topic further in our "Inertial Frames" video.
We are not offering a "new interpretation" of any theory, only pointing out a flaw in the current interpretation. Many interpretations and theories have had their flaws pointed out without new theories being offered up in their place... critical inquiry and skepticism are an important part of the philosophical and scientific process.
@@dialectphilosophy do you not agree that for an object to accelerate, a force has to be applied? And from that we can deduce that a force has been acted upon the spring? Or do you not like the idea that deduction has to be used to come to the solution that a force has been applied? Also, all the examples you have given in this video are situations where objects have accelerated away from type of inertial frame. Force can be applied without the need to for objects to accelerate, as I can squish an egg in my hand with force without the egg changing it's position. Furthermore, the situation where a person is in a empty room and sees an accelerometer change position and thinking that maybe it's just being affected by a magnet and not that a force is being acted on the building seems flawed. As I can exclaim that the moon is made out of cheese but that doesn't change any facts what the moon is really made out of. I don't know, if you could come with counter arguments to my comments, maybe that would make me understand what you are trying to say.
@付和雷同 One of the fundamental forces, or interactions, such as strong, weak, and electromagnetic, is not the same as a specific quantitative force, the F in Newton's F = ma. As far as gravitons are concerned, even if they exist it may never be possible to discover them.
I think the point is that a spring is now essentially a 3rd observer. With only 2 objects its not possible to tell, which is why I think the more simple explanation of two balls going opposite is maybe more valid.
Force is mass * acceleration. So I would look like a dead pancake if a train hit me. But if I sit inside the train im not sure if this is a accurate formula.
As regards to "Can we 'feel' force?" No, we can't -- not because how you explained it, but because "feeling" is a biological phenomenon and in Physics we DO NOT FEEL ANYTHING. We measure things. And let me tell you, YES, we can measure real forces by doing experiments. Of course Einstein's General Relativity has been formulated in such a way that the gravitational force has been done away with by redefining the effect of mass & energy on spacetime and vice versa, thereby bringing accelerated frames due to gravity within the realm of inertial frames of reference. But acceleration of a reference frame due to any other of the 3 forces of nature (as discovered till now) are definitely detectable by simple experiments within the frame of reference.
You ruin everything when you say "within the frame of reference"
@@fawzibriedj4441 Not sure what you meant. Nothing gets "ruined" in Physics.
Observations of experiments are also feelings. Otherwise I agree.
There's two different notions of "acceleration". One relative, one absolute.
I get what you're saying but to be fair physics gives rise to feelings and everything else about human experience. Unless you think its some kind of dualistic magic separate from everything else in the universe.
What I like about your channel, Dialect, is you always provoke thoughts and concepts to make one think again and understand better.
Summary 2:
An inertial frame is one such that no mechanical and/or optical experiments conducted completely within the frame can ever tell us about the motion of the frame. Whereas, in a non-inertial frame we can easily detect motion without any reference to outside, just by conducting certain experiments confined within the reference frame.
You mean, detect *acceleration*, not motion.
Fantastic. I hope you will tell us eventually more about the history and resolution of this discrepancy between your vision (Who else shares it? Does it have a name?) and that of the mainstream.
Inertia has nothing to do with "Feeling", it is simply the resistance to change in velocity. Or to put it in better terms it is the resistance to change from an inertial frame of reference. If two objects are accelerating away from each other there would have to be a force involved. This is why you can measure which train is actually accelerating. Since the force is only being applied initially to the train and not the objects inside it, the train will move relative to the objects until the objects come into contact with the train and the force is then applied to them via the wall or seat of the train pushing them forward. This is why if you had two trains in space with a ball inside each of them and only one accelerated away; the ball inside the accelerating train would seem to move relative to its train while the ball in the stationary train would appear to stay still relative to its train. This of course would stop once the acceleration stopped and both trains were moving at a constant velocity relative to each other again. This effect only occurs during the period of acceleration.
Hey thanks for the comment! If you define inertia locally via changes in velocity, then you are stuck at the fact that inertia will be relative, since all motion measurements are coordinative. That's why inertial frames are generally defined in reference to a global system, e.g. frames that aren't accelerating relative to the rest of the universe.
In your two-train example, consider instead the frame where the accelerating train is stationary. Now it is the ball which is accelerating away from it, as well as the other train and the other ball. There is no method in the context of the thought-experiment for determining whose acceleration is "more real" than the others. You simply have two distinct but equally valid descriptions of the situation: one description where one train is accelerating away, and another description where two balls and the other train is accelerating. Neither acceleration can be "more correct" until you introduce some further feature distinguishing them.
@@dialectphilosophy So just to make sure I understand your stance; you are disagreeing with the Einstein himself as well as the entire physics community about the fact that acceleration is not relative? You believe that acceleration is relative in the same way as velocity? That given a discrete energy input, the change in relative velocity for one object is the same as all other objects being moved instead? Or do you simply not believe in energy and forces at all? Do you believe that the resistance to a change in relative velocity (inertia) doesnt exist?
@@WizardsOfTheGhost No we are not disagreeing with Einstein; Einstein actually agreed with our position, and it was part of his inspiration for developing GR. Our argument regards the locally un-definability of inertial frames. One could potentially argue a consequence of this un-definability is that acceleration must be made relative in some manner. However, the typical argument is that something else lends inertial frames their objective character (this was Einstein's stance). Acceleration, in-and-of-itself, cannot be responsible, since its definition is purely mathematical/coordinative.
@@dialectphilosophy Inertial frames are definable and can be tested and observed. For acceleration to continue, a force needs to be continuously applied. Which is why if you were accelerating in a direction and let go of an object you were holding it would not continue to accelerate unless the force were also applied to it separate from you. Without force objects do not change between inertial frames. Its the exact reason gravity works. Gravity is literally just acceleration caused by the warping of spacetime.
@@WizardsOfTheGhost
Huh, no... Gravity lets you experience relative acceleration without the absolute acceleration that's the topic here.
It's only when you fall against a planet, that you're "accelerated" absolutely by the surface of the planet. And then you've ceased to accelerate relative to your coordinate system.
The very same kind of problem exists with mass actually, as you could always rescale it. In fact, in a world with only electric fields/interactions, there is no way to discriminate the (absolute) motions of similar q/m physical objects. This excess "freedom" should convince you that there is some kind of redundancy in these charges, or that there has to exist another fundamental interaction that would "split" those (as in, there should exist a physical experiment involving other interactions that are able to discriminate the motion of two similar q/m physical objects)
Dialect, you got it wrong! Force & Acceleration both exist and are independent of your feelings. And force does not cause acceleration only, instead it could just increase mass or energy of an object without accelerating it!
No, force and four-acceleration are merely assumed by the frameworks of the theories to exist absolutely. See our video "Newton vs. Mach" for further insight into this subject.
AFAIK when you ‘feel’ a force you are feeling compression or decompression. This happens to all objects that are not a single dimensionless point, so therefore all objects. Even in a gravity field some atoms of an object will be closer to the center than others and experience it slightly differently. Of course that would be hard to measure, but that isn’t the point. Our mathematical approximations can’t distinguish which element is moving, but that is only because it is an approximation using dimensionless points that don’t exist.
I could be wrong, so I’m curious how compression/decompression fits into this idea. Perhaps you can’t tell which atom is causing the compression, or which proton for that matter, but isn’t the whole body feeling a force if it is compressing?
3:30
You talk about a train accelerating "smoothly enough so you don't notice it" but if I had an accelerometer (such as a 2 masses held together by a spring) that could measure to ARBITRARY PRECISION, then you'd always be able to tell whether you're the one accelerating or not, even if it's not noticable enough to feel with the limited human body. In other words, you can always tell whether your frame of reference is inertial or not. Acceleration is objective!
As discussed in "Newton vs. Mach" an accelerometer has to be calibrated beforehand in order to make any sense of its readings, and so does not measure absolute acceleration (which is an undefined and non-sensical concept) but rather acceleration relative to the frame of calibration.
@@dialectphilosophyand in inertial frame accelerometer will show the same result regardless of it's direction, you can simply rotate it and if the lenght of a spring is different along the specific direction it is an accelerated frame. Otherwise it is an inertial frame.
@@dialectphilosophy Can't we just measure acceleration by, say, throwing a ball or ejecting a bullet in a direction perpendicular to the supposed direction of acceleration, and then observe whether the projectile follows a straight path? If the object follows a straight path we know we are in an inertial frame, otherwise a curved path would indicate that we are accelerating!
This is a truly physical channel. Thanks, Dialect. In my opinion, an observer doesn't have mass, so no "feeling".
Observing means interacting. You can't observe without receiving something (light,...). And if you receive something, you yourself must be an entity (object,...) within the system. In physics there's no such thing as a "neutral" observer.
Given the example of the twins in space with no reference. If one did accelerate away from the other, wouldn't they be able to deduce who is the one that accelerated? Let us assume that Alice accelerated away from Bob and both of them had a frictionless surface with a ball on it. Alice would see the ball move to the back of the plane whereas Bob would not. Given that there is no other information in the universe, then we can demonstrate that Alice is indeed accelerating and Bob is not. In the video, the explanation (5:00) would be that there is no way to tell if your refrence frame is accelerating because it can be due to some other mechanism that is moving it. Is it reasonable to state that there is no mechanism in this situation or would that count as measurement information?
Hey Mark, great questions! The issue with accelerometers here is that in order to associate a coordinate acceleration with a real acceleration, you first need to have an inertial frame. But once you take the twins out of the regular universe and put them in empty space, you lose any way to define an inertial frame. If you ascribe to Alice and Bob total knowledge of all the universe, and insert an accelerometer that distinguishes one of the twins' accelerations, then what you are asserting is that it is the addition of the accelerometer that is responsible for the definition of the inertial frame, and hence the breaking of the symmetry, which would in turn imply that your measurement tool somehow creates your reality.
@@dialectphilosophy I think it's resolved by the twins starting together, and one twin pushes something away from itself to accelerate. Whether they carry an accelerometer that is inaccurate or not doesn't matter, it's the twin that pushes something away that experienced more acceleration.
@@alexjohnward Exactly!! Yes, I've been trying to mention this on other videos of the twin paradox including one of Dialect's videos as well (I think anyway). This is a crucial piece they always leave out. The only way to accelerate is to exchange momentum with something else. This is literally in Newton's laws. You can compare your motion to the thing that you exchanged momentum with, whether that is something outside you interacted with (pushing an object) or ejecting a part of yourself (like a rocket).
I think one can tell if it is on an inertial frame of reference or not by checking homogeneity and isotropy of space and homogeneity of time, rather than in a "feel force" argument. I belive the first method is really clear and unambiguous and the fact that we see objects accelerate is a consequence of interaction. From and accelerating object due to interaction one can check that objects which don't interact (this may be where the argument may be weaker) break this frame of reference spacetime symmetry properties.
In "Spacetime Physics", Taylor and Wheeler define an inertial reference frame as follows: "A reference frame is said to be inertial in a certain region of space and time when, throughout that region of spacetime, and within some specified accuracy, every test particle that is initially at rest remains at rest, and every test particle that is initially in motion continues that motion without change in speed or in direction." According to this definition, inertial frames are always local ones. An accelerating elevator in free fall can be an inertial reference frame.
Acceleration is simply a change in your worldline vector. The change requires energy. The force we feel is nerve endings in the mass of our bodies sensing is moving from our initial state, sending signals to the brain. We can also see water in a bucket, or changes on an accelerometer.
Ok, maybe I'll look like an idiot here, but something is off in the thought experiment. When you're in a free fall, there is a spaghettification effect (your feet are slightly more attracted than your head) and thus, I can tell if there is a gravitational field around.
I know that GR speculates that the "free falling object" is a size-less point. But then we cannot apply the reasoning of an apple (which has a size) and say it does not feel the acceleration.
In the example of the passenger in a train, why does he feel the acceleration ? Because the train pushes the seat, then the seat pushes on the back of the passenger, etc. That's the equivalent of the spaghettification in acceleration. The reason why we don't feel like the passenger in a train when we are falling is because the gravity field is very smooth (almost continuously spread) and each part of the falling object is accelerating *almost* together at *almost* the same time. But that does not mean that there is not a theoretical/measurable difference.
Just wanted to say that I love your videos. We need more of these!! :)
I have never been taught that forces are “felt”, only that forces act on objects to change their motion.
Some people say the object "feels" a force (meaning that the force acts on the object) but they just say it as a figure of speech but it can be confusing because it sounds like the object is literally eperiencing a sensation, which isn't the case.
If you're in the car and accelerating, you can feel an effect of the acceleration, which is that you get a bit squashed against the seat. That's not the force itself that you're sensing. It's a biproduct of the acceleration which is that you get a bit squashed.
Inertial means that a mass is giving a resistance against changing its movement away from what ever straight path thru spacetime it is taking at the moment.
For example the accelerometer in our ears measures forces thru the liquid that wants to keep its initial movement and therefor is moving relative to our body if the body experiences a force.
So you can actually feel a force working on your body.
Yes, acceleration is one potential result of a force, but it can be resisted by a counteracting static force due to molecular forces causing friction and strain in the mass. So force is measurable. Force will change the velocity of mass if it is no restrained by an opposing force so again you can measure it my measuring the force required to prevent a change in velocity of the mass.
This video is great and make a very compelling argument, but there is still one thing that confuse me.
Let's say there is 2 boxes each with measuring instruments and one person inside in an otherwise empty universe, the boxes start next to one another with no speed relative to each other, then, the distance between the boxes start increasing faster and faster, let's say it increase like d(t) = t². In this situation as you point out, each of the boxes' passengers has an equal right to say that they are static while the other is accelerating or vice-versa, but! Let's now say that in one of the boxes, the passenger experience a constant push in the direction of the other box and the instruments on board read an "acceleration" a(t) = 2, meanwhile, in the other box, the passenger doesn't feel anything and the onboard instruments read 0. My question is, since acceleration is relative and each passenger has an equal right to claim that it is the other that is accelerating, where does the first box's passenger's experience and instrument's reading come from? How do we explain them? Does it have to do with space-time curvature?
Pure classic philosophy. Thought-inspiring, but for other purposes it feels quite useless. And I guess the same reasoning can be applied to any physics concept. (What is mass/time/distance “REALLY”?).
All the greatest changes in physics started out as philosophical questioning!
What is energy?
@@zhangkevin6748an integral of motion that occurs due to the invariance of Lagrangian relative to time changes.
Energy is the thing that changes when work is done. In another sense it’s the ability to do work.
@@CausalDiscoverieswhat is word done? Circular reasoning
Man, I came here for answers and I am leaving with even more questions. Kudos.
(7:55) I have always assumed that my grocer has a spring in his scale, so you can only imagine my astonishment when he used the theory of relativity to weight my tomatoes!
We speak of "feeling" a force because we have the acceleration detection machinery built in, so it is something everyone is aware of, but obviously the phenomenon exists absent any knowledge of it. But in the imagined room with suspended ball, the person in the room would also experience the acceleration in other ways than observing the ball. The idea that it's impossible to know if your observer frame is inertial by local tests, as opposed to observation of other objects, is false. There are many reliable "blind" tests for acceleration.
omg I was always so confused when my teacher said f = ma was determined "experimentally" and was like "if it's measured in kg.m/s² because of the formula, how would he know before coming up with it how to measure it anyways?"
This is a very interesting video, but I think you are missing one point.
No object is really solid. All objects, even the most solid objects behave in a way like a spring.
This means that when a force is applied to an object, it is usually not applied homogeneously on all its parts, but mostly on one part.
So when a force is applied to an object, the acceleration is not applied instantly to all its parts, but applied first to one part, causing the object to shrink slightly.
The shrinking increases the inner tension forces, which causes the rest of the object to accelerate at the same rate.
Try imagining accelerating a spring by pushing it, and you will see what I mean.
This shrinking is what activates your nerves, but you can technically measure it by other methods.
You do not need the surroundings to know that a force is applied to you.
In the example of the accelerometer in a closed room, you forgot that the person is going to feel a force due to the non-homogeneous acceleration applied to him. That is, his feet will accelerate before his head.
Even if the non-homogeneous acceleration is too slight to detect by human senses, (like the example of the train) it is still measurable by more subtle devices.
If you would apply the force homogeneously to all parts of the object, perhaps like with a charged body in an electric or magnetic field, theoretically you can create an accelerating frame of reference with real undetectable force.
You should be abke to still detect electrical forces by changing/transferring charge between the objects in your reference frame, which will cause force changes and acceleration changes in those objects.
And for superficial charges, the force will be non homogeneous too.
If one imagines that to any single atom of your body is connected a infinitely thin and massles string and each string in turn is hooked, on the other edge, to an object that may accelerate, then your body will never experience the feeling of acceleration, because all atoms behave like a single object. That's in my opinion, how fields work.
From what I understand proper acceleration is simply a mechanical force applied on the object, it may not even have a coordinate component. Just stress on the mass. Say in the context of general relativity when a vessel accelerates just to stay in one position in an orbital free fall.
Tell me please how conservation of linear momentum would work with relative acceleration.
You can always deduce if you are in a accelerating train with a ball, if it was at rest and stays at rest it is not an accelerating train but if it doesn't stay at rest it is an accelerating train.
I am enjoying your videos. Keep up the great work.
Acceleration is the change of velocity so increases and decreases of speed are both considered acceleration.
I love your video on the metric tensor so I arrived here. Quick side note: the fact that a force causes an acceleration is not metaphysics, that is physics as defined by Newton. 'Feel' is associated with the biological conception of sensation and perception. Biological organisms can 'feel' forces, but does an electron 'feel' the electromagnetic force from other charged objects? That is metaphysics. We know things 'experience' forces, thus things move.
We may miss the feeling of force when a train accelerates smoothly enough....because the acceleration is very small ...and we are often not paying too much attention to it. But that does not mean the feeling is not there. But great video....got me into thinking over the basics again.
Yeah but that feeling is caused by the seat’s matter hitting your body, and the effect it has on it is exactly the same it would have had if it was you who hit the seat. You still cannot discern whether it is you who is accelerating or the train.
If you were born free falling in a uniform gravitational field, and lived your life in free fall, and made free falling friends, you would never know that gravity exists and you would say you are inertial cause there are no forces acting on you. Your friends would also agree on the motion you describe for other objects, like kicking a ball (thus accelerating). This is what happens with our solar system. It is being accelerated uniformly by gravity coming from far away, and you BELIEVE it’s inertial because we all agree on accelerations outside the free fall.
On the other hand if the gravitational field were not uniform, you would see other objects far from you accelerating and others would see those objects accelerating but you would disagree on the acceleration, because both observers are differently accelerated. A third person somewhere else would see you and the second person accelerating IN A DIFFERENT WAY that you and the second person see each other.
Inertial frames may agree on accelerations, but accelerated people don’t. But no real inertial frame exists cause it’s impossible to tell if you are truly inertial. All the “accelerated” observers felt inertial in their frame of reference. The word “fictitious force” is what inertial observes named the forces they don’t perceive, implying that what they see is real, but an inertial frame can only be a local thing. For an inertial frame to be global you must have no interactions. There’s no such thing in the Universe.
Summary: there is no global inertial frame only local.
Those who agree on accelerations are just being accelerated in the same way, as if in a uniform gravity field.
Those who don’t agree on accelerations are just being accelerated differently.
In both cases, they are locally inertial, but the former insist they are globally inertial, just cause they have more people backing them up 😂
@dajmo. isnt thats why newton proposed every force has an equal but opp reaction. its not just for conservatio. of momentum.
@@_Xeto We are indeed in a free fall under the Sun’s gravitational pull…. So we do not really feel Sun’s attractive force. It’s the hard crest of planet earth that does not let us freely sink to the centre of the Earth under earth’s gravitational pull … therefore we feel earth’s gravity.
@@dajmo2369 Either way, there's a force
Great video!! Continue doing them please.
Just one question: if I am in a closed room and attach an accelerometer to the wall, that says 9.8m/S2, can I ensure that I am not in an inertial frame of reference?
That answer depends on your relative knowledge of the system; are you familiar with the accelerometer instrument, have you properly calibrated it prior in an inertial frame, can you guarantee that nothing else might be causing the accelerometer to move? etc.
@@dialectphilosophy ok, then assume
- I am in our real universe
- I calibrated it prior in an inertial frame( not necessary if i am using my laser beam method)
- nothing else might be causing the accelerometer to move
- the definition of inertial frame is just the same as in general relativity, where acceleration is still absolute.
Forces exist whether we feel them or not. Can you feel the magnetic lines of force acting on iron filings around a magnet or on a compass needle? Nevertheless, the force is empirically evident. No feelings required.
2:46 I feel like this part needs to be elaborated more because it was confusing to me. To my understanding, you need force in order to measure inertial mass and passive gravitational mass (fictitious force for the latter perhaps). I can see that force is not needed for active gravitational mass, and if we can treat active gravitational mass and inertial mass as equivalents (because there's no evidence of deviation so far), then that part made sense. Though, I'm still unsure if that's what you were arguing.
There are some serious flaws and your reasoning here.
1. Not feeling the acceleration when is a vehicle that starts up slowly and smoothly it's simply a result of the acceleration being too small for you to feel. That is it is simply too small to be detected by our senses. That does not mean that the acceleration and the force or not absolute, just if they are too small for you to notice.
2. Your illustration of the accelerometer in a room that most likely is not accelerating is not a problem with being able to measure an actual acceleration, both of the possible causes that you gave are a result of someone applying a force to the pendulum. Hence the problem is, that you do not have it honest accelerometer, the one that has been rigged by someone deliberately trying to trick you.
The fundamental flaw in your argument is the simple fact that acceleration is locally measurable. For example, the Earth's rotation can be measured with an interferometer that sends light in two opposite directions, if it is big enough. Basically what you were doing in this video is, relying on an acceleration that is below perceptibility, and someone trying to trick you by applying a force to the pendulum. Neither of these, actually indicates that acceleration is not absolute. However, the fact that we can feel it when acceleration is high enough, and the fact that acceleration can be measured, when the device is functioning properly, shows that acceleration can be locally measured without any reference to the outside universe.
You can simply deduce force by asking 'Am i being detained?'
Objective measurement of force lol
Being pushed into the seat is not the feeling of your acceleration - rather, it's the feeling of the car's acceleration! If you were made of metal, and both you, and the car were accelerated by a magnet, you would not feel anything at all!
The train example that you give is floored. It just shows the fallible human sensors are. If you asked a accelerometer what was happening it would tell you.
Deduction of local orders of Kinematics means we assume our notion of space, velocity, acceleration etc have temporal-orders of 0,1,2,3,...
Yet this is a local assumption.
Imagine an observer that deduces what we observe as velocity (first-order) they observe as spacial coordinate (null-order).
Would relativity be relative to this shift in order???
A single particle doesn't "feel" force, but multiparticle systems do. Same with entropy. It's an interesting perspective, but it seems to show we don't fully understand the physical world. Our best theories are know to be wrong, good mathematical models for our context, but still wrong.
I am struggling to see the issue with thinking of acceleration as absolute. I don't think relative comparisons really need to come into it. It is a concept that stands on its own. You can add another object to your thought experiment if you like, and then see the implication for relative motion/position but it seems entirely optional and unnecessary for having a conception of acceleration.
In my understanding acceleration is fundamental to the definition of mass. I define mass as energy that resists acceleration. Anything with mass, even the most fundamental things, are composite entities that involve interactions between parts such as the Higs field or the quarks and gluons in hadrons. Without such interactions, the unencumbered energy would travel at c and have no mass.
In the photon box analogy, there is a pressure on the back side of the box when a force accelerates the object, which could just as well be a neutron, a quark, a person or a cheese burger. In all cases where there is mass there is something confining energy, preventing it from traveling at c creating an asymmetry in pressure when it is accelerated that resists said acceleration.
I could be wrong but I have listened to your arguments multiple times and I have failed to be convinced that we need to think of acceleration as a purely relative phenomenon.
These videos are great. My only question is when you say 'force', do you just mean gravitational force? As you reference General Relativity. Or do you mean ALL forces? For example, are you claiming that the Electro-Magnetic Force is a curvature in some Electro-Magnetic Field? Strong/Weak Nuclear forces, are curvatures in Strong/Weak Nuclear Fields?
I'm just trying to wrap my head around the property of charge.
This video is regarding the classical definition of "force" as described by _Newtonian_ mechanics and the _Lorentz_ force for electrodynamics, so all contact and inertia (pseudo/fictional) forces on bodies with inertial and gravitational mass.
The classical force was created with calculus and differential equation to determine causality, the action, change in momentum, and the path of point mass that deviates from a straight world line and being accelerated by a force.
The video briefly mentions that in Quantum Field Theory, the concept of a "force" has been abandoned. The classical field theory of electromagnetism, _Special_ relativity, and _General_ relativity can be approximated using forces and field theory.
The fundamental interactions and elementary particles (except gravity) are described as "excitations in quantum fields," rather than "curvature." Spacetime curvature versus flatness is something different.
None of this makes sense if we consider gravity a force.
Gravity can't be a force, because for us someone freely falling due to gravity doesn't experience absolute acceleration. Only the relative kind.
Absolute acceleration is what is responsible for time dilation.
"Feeling" is a perfectly valid scientific measurement. The only problem is that it's much less reliable than most technical measurement apparatuses.
idk what about a *roller coaster?* like yeah i know that i am in it an can see stuff moving around me going faster, but I can feel being pushed into the back of my seat as it speeds up, or being pulled out of it from the centrifugal force when it spins.
Profound stuff - sure to piss off the Star Wars fans! But seriously, you’re onto something here. Make some more videos, soon. All the best. A fellow astute thinker. 😊
p.s. you can't directly measure velocity, energy etc. either. Physics is bootstrapping and we could "easily" replace it with others, whilst not having the foggiest about what's "really" going on. There is no escape from this
when you think about it, the only thing we ever really measure is distance and how it changes. Time? A clock has something that moves a certain distance at a regular time interval. Velocity? We measure the change in distance per unit time. Acceleration? We measure the change in velocity per unit time. Mass? A scale measures the distance a spring is compressed.
Wouldn't this make gravity and acceleration the same? Since gravity is the amount of energy which creates the force and accelerating is adding energy to move an object therefore making it the same as gravity but with a different kind of energy?
This channel is freakin underrated.
With any rotation isn't it plausible to know you're in an non inertial frame of reference, since distant objects appear to be moving faster than light? I agree with what you've said in the video, just confused with rotating reference frames.
Hey, thanks for watching! In GR, the speed of light is only constant locally; so in more global frames objects can move faster than the speed of light. This would likely indeed indicate a rotating or non-inertial reference frame. In this video here we suggest the possibility that force could be relative on a local scale, but on more global scales force is easily discerned through these sorts of fashions.
@@dialectphilosophy In which "global frames" can an object move faster than the speed of light?
We are in a universe. in that universe, the speed limit is the speed of light (although it's actually the speed of causality ), PERIOD!
BUT, we are in a expanding spacetime, so teorectically we would be moving at a speed higher than the speed of light.
But it would be like an ant moving in a piece of elastic fabric. If the speed of the ant would be its speed plus the speed in which the fabric is expanding.
You said "the speed of light is only constant locally". That is not true. Speed of light is the speed of causality and has the same value, unless it changes the medium, in this case, the photons interact with the new medium and it looks as if the speed is less than in vacuum, but this is well explained by Maxwell equations.
@@ranyeredt "Speed of light is the speed of causality" - Wrong. You can believe that philosophically, but the science does not show that. Science deals with observables only. It does not support claims about causation. Science is built upon reproducibility. It is built upon peer review. It is always up for adjustments when new theories are devised that provide better explanations than current ones. As such, it can not support claims about causation.
"we are in a expanding spacetime" - in other words "I have bought into everything mainstream physics education tells me to think, regardless of how ridiculous it is". Inflationary cosmology is just a theory. It is still disputed somewhat. It is not absolute. Modern education is seriously lacking when it comes to teaching philosophy, logic, and skepticism.
@@dialectphilosophy In GR, the speed of light is only constant locally?
Are you sure?
Here is simpler one. Two objects in free fall will deduce that they are not acclerating relative to each other. they "feel" they are not accelerating.
Yeah, because they are not accelerating by the GR rules. They seem to acceletate in a non-inertial ref frame of a planet they are falling to, however we do not care about Non-inertial frames, you can say the Universe revolves around you while you are rotating, it does not mean anything. That is why gravity is a false force in GR, like Coriolis force: they are forces only in non-inertial frames.
From the beginning I was skeptical that if velocities are relative so should be acceleration. So am I feeling the force or the reference frame. is force even real?
"feeling" and "seeing" aside, surely by one pressing the throttle pedal you know you are mechanically applying "force" and causing accelerating and the other who is doing nothing is not given all else equal ... how would one translate this to absolute acceleration? ...
The "co moving" reference frame in which the CMB is the same temp in all directions really seems like a universal reference frame. Even though it's not.
But, if you wanted to compare a point in space with literally everything else, it's about as good as it gets.
Im probably wrong.😊
8:49 "We have no knowledge of profound causes of force"
What makes you think that? Force is a name given to two or many physical and observable quantities it seems
Curious to know your perspective!
F=ma. Force equals Acceleration. Acceleration creates Acceleration.
The universe is a series of chain reactions. A perpetual motion machine.
What we don't know, and possibly never will. Is what the initial acceleration event was.
F=ma describes an infinite, unbounded universe. Everything and yet nothing at all.
The God 'said' Let there be light.
God was what started the chain reaction. Changed F=ma to E=mc a finite universe bounded by the speed of light.
E=mc. Acceleration creates distance. Distance is length. Length is an attribute of space/mass. Acceleration creates space. Creates time. Creates the universe. Defines the universe.
The 64,000 dollar question is, who are what triggered the initial acceleration event?
@@stewiesaidthat
i think you understand nothing about F=ma because creator said i will stop the universe when i will find no people doing good so who are you to say that the universe is not infinitely finite? Because creator creates infinity and that infinity is also finite for him because he creates that. Creator is above everything so stop being stupid and don't start to lump religion with science because true religion is the word of creator so to understand it we need more knowledge and science is just a part of that knowledge nothing more than that which always changes and somethings will never change as they are truth and force is empirical truth so earn knowledge and study how to be a good philosopher not a bad one because knowledge is all. Moreover, general relativity never showed force doesn't exist rsther it showed force can exist in geometric shapes. Only misleading science persons who don't understand math equations will say that general relativity denies force. Man we really do live in a universe that is full of misleading people now. Do you even know anything about electro magnetic permittivity and nasa even found electro magnetic permittivity in space which is empirical.
@@ourfamily.zsl5 What’s the name of your religious view?
It’s interesting to learn other perspectives, but when you claim to be 100% right, and everyone else is 100% wrong, you won’t persuade anyone.
The world has many religions and sub-religions. On a scientific channel, I think it’s best to limit to scientific evidence and not involve religion. You can create religious videos to speak from another perspective.
@@ian-flanagan
Bro so lame. Haven't you read about the comment i have replied? I was showing him another one tone told by religion so handling science with religion is the problem. Religion is the word of the creator and you don't know how you will prove them until science shows some empirical evidence. I wa never showing you i am correct. O just showed you what logic and math is saying. Lame and you start talking about being adamant but it is you who is a big fan of your own words.
@@ourfamily.zsl5 Do you think calling people wrong and lame will make more or less like your Creator?
I'm not really sure what your goal is here
When reading about General Relativity, one claim I encountered frequently was the justification for gravity not being a force. It goes like this: Imagine you are in freefall. You won't feel a force acting on you, even though you're being accelerated by gravity. On the other hand, if you're in a car that's accelerating, you will feel it. Therefore, gravity is not a force but a warping of spacetime.
Took me a long time to see that this is nonsense.
Yeah it's good point to raise; "force" is defined empirically via being able to measure weight or see deviations of free bodies, etc. All those definitions fail for gravity, which is why we have to say we're accelerating "up" at the surface of the earth. The alternative of course is to recognize that acceleration is relative and we just need to identify what we're accelerating relative to.
Force should be the first derivative of momentum, not simply acceleration, which does have an observable component namely it's conservation. This is to say inertia, or mass, itself. Inertia is the thing we 'feel' as we accelerate. For example when a proton colides with an object the majority of its mass is do to the internal 'collisions' of its quarks or rather to the exchange of gluons , creation and annellation of quarks and so on. Exactly the strong force. Also, for now most scientist assume gravity will be added to quantum mechanics not that strong, weak, and electromagnetic forces will be shown as illusory.
Defining force as the derivative of momentum is certainly no issues; but unfortunately it hardly resolves the problem. The conservation of momentum is a direct consequence of an inertial frame (i.e., in a non-inertial frame, momentum will not be conserved) so the definition only works so long as one is certain one's frame is inertial. To be certain one's frame is inertial means they have to be certain it is not accelerating... meaning they have to be certain the derivative of momentum is conserved... meaning they have to be certain their frame is inertial (repeat vicious cycle indefinitely...)
@@dialectphilosophy aren't the two directions orthogonal to the direction of acceleration conserved while the parallel direction not conserved.
Summary 1:
This simply means REAL ACCELERATIONs (not pseudo accelerations) ARE NOT COORDINATIVE AND HENCE THEY ARE NOT RELATIVE. This is because they can be detected from within the reference frame by performing simple experiments. However, constant speeds (including v = 0) is very much relative. That is, constant speed can't be detected without referring to the "outside" world.
Yep.
Imo the confusion is best cleared by saying that there's two entirely different notions of "acceleration" in physics.
There's are increase of internal stresses when accelerating. Which will not happened under other circumstances
If something breaks due to internal stress during acceleration in a rocket ship, an observer in the ship would not necessarily be able to explain it. We can't assume a frame of reference to have any knowledge, only to be able to observe motion. To a "dumb" observer on the ship, the fracture would be spontaneous and spooky. To an "intelligent" observer the fracture is explained by an increase in internal stress, a concept invented by man. Therefore, concepts such as force and stress are relative, observer-dependent concepts and can't be real, objective truths about nature.
I THINK that is is the point Dialect is making.
You cannot directly measure Time either. What you measure is a constant velocity over a constant distance. This is true with a classic clock whose hand moves around a circle off a given size at a constant velocity. This is also true with more sophisticated clocks, but the distance is a wave-length and the velocity is C.
You also cannot measure velocity absolutely. Instead you must compare distances traversed between two objects up to a "present moment" to determine a relative speed betweeen them.
@@beamshooter And, distance requires a ruler which is why we struggle to measure the distance to stars and galaxies.
I did not quite get why the accelerometer does not solve this? In another video you mention that it must be calibrated relative to something, which is true. But this is why we rely on fundamental constants to calibrate our SI base units to and assume these quantities stay constant as time progresses.
Physics has to be useful for predicting outcomes of experiments, enabling technologies. It is not concerned with the "true" nature of reality as long as it is not measurable. For all we know we could as well just be a boltzmann brain. Philosophy is an interesting field in and of itself, concerned with questions like "the ship of theseus" and the like. It has been helpful to physics and technology by posing new questions to ask. But you'll have to remind yourself that physics is mostly just concerned with frameworks for technologically useful predictions, everything else is "extra". As Descartes once said "I think therefore I am" we have to make reasonable assumptions from which we can build our frameworks upon.
There has to be some sort of value proposition to change views, albeit just an exploration out of curiosity.
When we measure systems to validate or develop theories of motion relevant to macroscopic objects do we ever involve anything other than electromagnetic forces now that we treat gravity as a curvature of space time? If not then is a relevant force just a deviation from some kind of electromagnetic equilibrium? Then is a frame shift actually a change in things like spin vector distribution but maybe other properties that add up to the appearance of special relativity?
Topic for a video: Mass or Weight or both actually the same?
In terms of observable linear momentum (assuming you're okay with that since mass is lumped in), can the video be summed up as the following statement? You can observe supplies but you can't know sources.
Acceleration is impossible without Force. But Force is not impossible without acceleration.
A static compressed spring held in your hand can give you the experience of force without any acceleration.
Please talk about the distinction between Internal and External forces in your video when you invoke the concept of Feeling Force.
Look forward to the resolution of the twin's paradox
Hey Dialect, I'm confused with this!
Consider a man in rotation where he has nothing in the universe for relating with (you know!). Then according to him, he is still. But if his arms are lifted up, we could understand that the man is in rotation. Doesn't it mean that there is something that can be said relative to even in the nothingness (maybe the space itself!).
What I mean is among all the possibilities, the man's arms are not lifted in only one scenario. And that is the case in which he is still (not rotating). So does the non-lifted arms mean that he is at rest relative to something eventhough we couldn't find any differences between any of the scenarios with our HUMAN PERCEPTIONS?
That's a great question -- it goes to the heart of Newton's Bucket Experiment / Mach's principle. When Einstein considered it, he felt that the lifting of the arms, if considered under Newtonian mechanics, could only be explained by adopting a "privileged space". But since such a space was not observable, he rejected the possibility of it and concluded that the cause for the lifting of the arms must lie outside the system.
So to summarize, in the Einstein view, if the person's arms are lifting, then there MUST be something observable beyond them which they are rotating with respect to. A person in empty space could never rotate to begin with. As to the point you make about human perceptions, if you are asserting that there might be some hidden variable that is not measurable but which exists and which distinguishes local rotation from non-rotation, that is an interesting idea perhaps, but it might prove tricky building an empirical theory around.
@@dialectphilosophy Thank you very much, Dialect! Let me get some knowledge of what you've said above, as I have no idea about what is 'privileged space' or whatsoever.
And a quick suggestion, if you add something behind your channel name, like 'Dialect - Exploring Science', that would be easy for your subscribers to search for your channel and that helps your channel to stand out among those creepy 'Language Dialect' channels, at least until you grow up(like VSauce!).
And that's totally your wish, that's just a suggestion!
Thank you very much!
There is no space-time
Force is derived from mass and acceleration. But how is mass determined except by testing it with forces?
So would be lagrangian and hamiltonian mechanics more consistent because we don't use the concept of force?
IN A AUTO DEATH ACCIDENT WHEN YOUR BRAIN GETS COMPLETELY FORCED TO ONE SIDE OF YOUR SKILL.......OH NO THAT WASN'T A FORCE !
Won't launching an object with mass and and a photon in parallel to each other let us distinguish an inertial frame from non-inertial one?
So feeling squished back into my seat isn't feeling a force? I'm lost.
You don't feel the force, you feel the collision of your matter on the seat. When you accelerate what you feel is your internal organs and tissues colliding and pushing each other as a result of different acceleration throughout your body, which is a macro system, because the force isn't being applied uniformly across your whole body. If the force were to be applied on all your molecules and atoms uniformly you wouldn't feel it, in fact you would think the whole universe just started accelerating in the opposite direction.
You've come up with lots of reasons why the question of acceleration can be problematic. To go from that and say it's RELATIVE is specious. An electrically neutral ball in a non-accelerating spacecraft floats freely. Then the engine is switched on and the ball is forced against the bulkhead in the direction of the engine and opposite the direction of acceleration. That is force and acceleration, absolutely, pure and simple. Feeling and coordinates have nothing to do with it.
All acceleration is defined relationally, meaning you cannot speak of acceleration without implying what you are accelerating relative to. The issue is not that acceleration is relative (since you cannot define it any other way) but why it acquires such a seemingly objective role in our empirical reality.
According to your engine's perspective, it might as well have been the ball which accelerated. The use of an accelerometer ultimately tells you nothing unless you inject certain a priori assumptions into your scenario, as we discuss in the video.
@@dialectphilosophy But acceleration is felt inside a ship not because you infer or deduce that you are the one that is moving, changing speed, accelerating, but because your mass is resisting change in speed (because of inertia) and your body is therefore pushed back into the seat. You are claiming, if I understand correctly, that acceleration is applied universally. But that's never the case. I feel your arguments always presupposes ideal point-like object. Also, your train example is misleading. You don't confuse the motion because you don't feel acceleration, but because the acceleration is just so weak. If you would accelerate with the force of 9 Gs, there won't be any confusion. And your fainting would prove that. (Again, even human body is not a point-like object.)
On the other hand, I like your thesis that force is mathematical abstraction. In the same way that energy is also mathematical abstraction, only defined as ability for something to do work. But after that your argument is flawed. Even if everything that is not empirical (that we are not able to measure it directly, whatever that means), is really an abstraction (here I am talking about force, energy, practically all physics), that does not mean these concepts aren't always referring back, through math, to the measurable phenomena. Force is always referring back to acceleration and mass.
@@petpaltea but who is to say that you are the one accellerating forward, and not the atoms in your body accellerating backwards and the spacecraft standing still?
you can't know, without knowing that the engine is on and pushing the entire craft forward.
if you are driving in a car at 60mph, and you put your hand out the window, who is to say that it is not the air moving into your hand, instead of your hand moving into the air.
who is to say it is you moving through space, and not space moving through you?
@@dialectphilosophy
Ok, maybe I'll look like an idiot here, but something is off in the thought experiment. When you're in a free fall, there is a spaghettification effect (your feet are slightly more attracted than your head) and thus, I can tell if there is a gravitational field around.
I know that GR speculates that the "free falling object" is a size-less point. But then we cannot apply the reasoning of an apple (which has a size) and say it does not feel the acceleration.
In the example of the passenger in a train, why does he feel the acceleration ? Because the train pushes the seat, then the seat pushes on the back of the passenger, etc. That's the equivalent of the spaghettification in acceleration. The reason why we don't feel like the passenger in a train when we are falling is because the gravity field is very smooth (almost continuously spread) and each part of the falling object is accelerating *almost* together at *almost* the same time. But that does not mean that there is not a theoretical/measurable difference.
Acceleration of the ball is felt simply because force applied to it is not uniformly spead. The outer of the ball touches the bulkhead, and the rest tries to resist the force thus is felt.
That's why they say gravity is not a force because its so equally spread that is applied uniformly in all areas thus not "felt" while it is still a force. I hope i make sense.
If in some magical way u could do the same for electric force (a negative source attracting a positive force) it would be the same. Of course electrical force acts in closer distances, thus one side of a ball would receive more force than the other side, but in gravity is we could discern this miniscule difference it would be exactly the same.
What about static force? Stress/stain measurements are made in solids all the time.
What about changing acceleration or accelerating changing acceleration? More philosophy…-ve speed or going slower than stopped. Accelerating into the stopped state. Figure it out!!!
A better question is that can you design a device that can detect if the current reference frame is accelerating or not and thus inertial or not, that way you can frame this video better than asking the question of whether we feel the acceleration of the frame of reference or not. The example with a pendulum inside an isolated room and the person deducing that there is a magnet behind the wall instead of deducing that the whole room is accelerating does not make a little bit of sense, I think you lost what you were trying to convey there as it is entirely possible to deduce from that event that the whole room is accelerating...
If you stick a knife in a light socket you're going to feel the electromagnetic force course through your body and give you a jolt.
Please correct me. Inertial and non inertial frame is distinguished through pseudo forces irrespective of knowledge about the surroundings. And pseudo forces is "observed at most qualitatively", and this pseudo forces is stated in "experimental" !st law of Newton.
Also i love the you care each word in a definition!!
Hi can you make some videos starting from the basics.
We are never in an inertial frame, so nothing can be really calibrated by men. But we are in a almost inertial frame and can well feel forces, in my opinion. Likewise, we can use an accelerometer and calibrate it up to a certain extent by using all 3 directions of space. And then we can measure accelerations with an error that is neglectable. Why would such a small error make such a big difference leading to the statement that we cannot feel force?
You could calibrate your accelerometer in as many directions as you like, but you could never guarantee that you weren't accelerating in those direction during the calibration process, so at best you could only obtain to probabilistic likelihood of experiencing force.
(Plus, if you want proof that the human body itself cannot differentiate true from apparent motion, go to a planetarium or one of those Disney park rides where the screen moves around you, and see how your mind reacts...)
I agree that we can easily be fooled by our eyes because we never really are attentive to the usually small external accelerations of our body. Also we are constantly accelerating our body or parts of it ourselves by moving around or playing tennis so that this is kind of natural to us. The steady massive external acceleration upwards we perceive as weight because it‘s so constant. But ask Louis Hamilton if he feels the force when he starts a race.
When freely falling towards earth you experience an acceleration as observed by a observer on earth. Yet you feel nothing as gravity acts on each atom of your body the same.
The acceleration felt in a train that is set into motion is only felt due to it acting on only some parts of your body that are in contact with the train, resulting in a force differential that can be felt by your Proprioception.
Now lets say the whole universe started to accelerate in some direction. That is your very most basic inertial reference frame is accelerating from you, would you be able to tell it does?
I find it interesting that you decided to draw in a midnight dump in the middle of the field 0:25
If you see waves on an ocean are you not seeing a force? The water itself only moves up and down but the waves move
So what about stress vs strain relationships in materials? Take steel for instance, we know it starts to yield at about 275 MPa, and this has been measured and tested in labs across the world. So why do these materials behave so predictably with regards to feeling a force if its such a mysterious phenomena?
If you apply a 275 MPa force to an entire piece of steel that is free of all other external forces, then it will simply accelerate the entire piece of steel, and the steel will not bend. This is the kind of “force” he’s talking about in the video. You’re talking about fixing a piece of steel to a large mass, and applying a force to a part of the steel body that is not fixed, which is really a different situation.
@@mensaswede4028 why won't it be subject to bending, or any other type of stress..?
@@dannylad1600 Because the force is applied evenly over the whole object (in the situation that the video is talking about)
@@mensaswede4028 well if that's the case then the object will be subject to axial stress. If it's not evenly supported than it will also bending moments and even shear stresses as well. Either way, if the steel object is being accelerated then it's going to experience stress of some kind.
@@dannylad1600 Not if every atom of the steel object receives the same force equally.
You guys are so smart,all of you!
If your accelerometer is faulty, you will have faulty understandings... if the accelerometer is accurate, you will determine that the room is undergoing acceleration, even if you think it implausible.
Great video. One of the few that tries to be rigorously logical. What I am confused about is compression and tidal forces. If someone if punched the area where there are punched becomes compressed. If I can tell where a force is applied doesn't that me a force was applied? In the same way one's back is compressed when a train accelerates forward..
To address your compression question: consider matter with two states, compressed and uncompressed, as measured relative to some standard. Now, the question becomes, is the compressed state the inertial rest state, or is the un-compressed state the inertial rest state? The only way to really know the difference is for there to have been measurements already made of the material's natural compression state in a frame known to be inertial. Thus you couldn't ultimately use something like compression to define what a non-inertial force is.
@@dialectphilosophy Thank you for addressing my question. You video is a real break through. I still do not think you answered my question. "The only way to really know the difference is for there to have been measurements already made of the material's natural compression state in a frame known to be inertial." Why can't I measure the service area of the object. Why can't I know if the surface area deformed? The point is. "The only way to really know the difference is for there to have been measurements already made of the material's natural compression state in a frame known to be inertial." We must have measurements of some kind or were couldn't identify the object or know that I exists. If you are talking about an unknown object or an unknowable object then your point becomes meaningless. They is something you aren't saying or some assumption that you have that I do not.
@@TomTom-rh5gk You’re probably overthinking it just a little. You certainly can make measurements of surface area, compression or whatever else you’d like. But those measurements would just be meaningless numbers if you don’t have an inertial reference system to compare them to.
@@dialectphilosophy No, I am under thinking it . There is something you haven't explained. You say, "But those measurements would just be meaningless numbers if you don’t have an inertial reference system to compare them to." 1. Inertia is the inertial reference system. Inertia is the most basic property of an object. Without inertia, you do not have an object. 2. Without inertia an object changes for no reason because It lacks identity. 3. Without inertia you have nothing. You can’t even say that something accelerated because there is no something.
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I think your explanation is missing something. Everything you said made so much sense that you must have a hidden assumption that you need to express in words.
@@TomTom-rh5gk We recommend you check out our other videos, particularly Newton vs. Mach, for further clarification.
Isn't my stationary body an inertial frame by which I can feel whatever force that acts upon it?
Does not a glass of water provide an observable change in motion? F=m×a is not just an illusion.