Doctor Lincoln, I've watched many of your lectures. You are indeed a remarkable teacher. Thank you for showing all of us that physics is for everybody!! Well done!
To piggy back on this top comment, I would like to mention that the equivalence principle is NOT Einstein's idea. As Dr. Lincoln himself states, this idea dates back to Galileo. But he, like everyone else, attributes this to Einstein falsely. Furthermore there are many issues with the equivalence principle in general relativity that is not often discussed among the public but has been extensively discussed among general relativity experts. Einstein changed the requirements of the equivalence principle at least twice and deluded himself into believing it is a secondary consequence of general covariance. His early formulation of the equivalence principle (before 1933) was incorrect. Einstein did not understand "his" theory of general relativity because all the dirty work was formulated mathematically by Grossmann and Hilbert.
You forgot to mention Galileo's superb 'reductio ad absurdum' regarding this matter. Let's suppose heavier objects fall faster than light objects. Imagine two heavy objects (A and B), one weighs 2 pounds (A), and one weighs 1 pound (B). Imagine connecting these two objects with a string. if heavier objects fall faster than light objects, then the lighter object B, will act as a drag on the heavier object when we drop our tethered weights off a tower. So A will fall slower than it would if untied to B. But A and B tied together weigh more, so the combined weights should actually fall faster than the heavier weight alone. So the combined objects should fall both slower, and faster, than the heavier object (A) alone. That's a manifest contradiction. So we now know that our initial premise (heavier things fall faster than light things) is manifestly wrong. It has to be false. And we don't even have to leave the house to drop weights off a tower to prove it.
Except that someone could probably come up with a definition of "object" involving rigidity and mass distribution that would disqualify the two balls and string from being treated as a single one. Anyway, the fact that they do fall at the same rate shows the two types of mass are the same, no need to invoke GR.
Ni there's no contradiction, just a missunderstanding of how gravity on your side. Gravity is due to mass, but density does matter because gravity also depends on distance. A more dense object of a given mass is smaller, so you can get closer to its centre of mass and experience a stronger gravitational force. Second, density is also related to mass which means that an object with more density needs a smaller volume to have the same weight as an object with less density. Gravity is dependant on mass and the distance between the two objects. ... However, just going purely on the equation, gravity has no dependence on density. An object with twice as much mass will exert twice as much gravitational pull on other objects. The gravitational force increases as the size of an object increases. On the other hand, the strength of gravity is inversely related to the square of the distance between two objects. The weight of an object is the force of gravity on the object and may be defined as the mass times the acceleration of gravity, w = mg. Since the weight is a force, its SI unit is the newton. Density is mass/volume. The density of water is 1000 kg/cubic meters at 4 Celsius. In physics, the weight of the substance differs from its mass. The weight is the gravitational force that pulls any object to Earth. The specific weight corresponds to the weight per unit of the volume and can be calculated from the specific gravity.
Take something that everyone knows, what is essentially, "common sense" and show us just how mind blowingly awesome it actually is. You'd think by now, having seen so many of your videos that it would be expected, but you just keep surprising me.
just when you thought you were beginning to understand some basic concepts of the universe after thirty years of teaching physics, someone comes along and in a few short videos completely opens up a whole new way of seeing things. absolutely stunning. I will definitely be including these 10mins video at the end of each lesson.
Technically gravitational mass and inertial mass could be perfectly linearly related by Mi =kMg. For example, if you use a gravitational constant that is 4 times larger, then you would have gravitational mass 2 times smaller than the inertial mass, and all the equations would still work out (k=2). If we just set the constant to 1 it works out that they are equal, but there is nothing you can derive that says it is 1. It's an axiom.
@matttonkthetank5619 nice catch! I came here to make a similar comment. So, the observation that all of the objects we try experience identical acceleration in a gravitational field only shows that Mi/Mg is constant, not necessarily 1. And I'm also tempted to ask for how many kinds of objects and with what precision we've verified this. Truly, for experiments like Galileo's and Cox's, the answers would have to be "only a few" and "not with very much precision". But I guess people who build rockets have by now found it to be reliably enough constant that their rockets have behaved very precisely, regardless of payload contents. For example, being able to slingshot from one planet to another seems like a very precise activity.
And I agree with you. But the consequences of this could be very large-scale. Does anyone know if there are theories in which inertial and gravitational mass are not equal, but only proportional?
@@faberant I'm not qualified to answer that question. But in the video, Dr. Lincoln says that Einstein set the two quantities identical in his General Relativity derivations (I have no idea where that came in). If they were not identical, but only proportional, perhaps such a change to one of his assumptions would have forced differences in that theory. And perhaps such an alternative theory would give different predictions than G.R. which one could then test, or maybe some such predictions have already been tested.
I am not a physicist, just passionate about physics. But I do understand that what Dr. Lincoln is trying to tell us in this video, and which is actually mind-blowing, is that at the end of the day, we still don’t know why objects fall. Because of the gravity say physics books since Newton. But what the heck is gravity? It should be an electromagnetic charge, but it doesn’t behave as such. Because then lighter objects, not heavier ones, should fall faster. Along comes Einstein and says that there is no such thing as gravity (makes sense), and things fall because of the curvature of the space-time fabric. So which one is it then: gravity or space-time curvature? Physics still doesn’t know the answer, and this is really mind-blowing.
X and Y are variables and just because they're equal doesn't mean they're the same variable. The distiction is important for understanding and in the case that our fundementals change. Which it may in the pursuit of a unifying theory of quantum and gravity.
@@lazycouch1 Just because you use different variables doesn't mean the quantities represented are different. As far as we are able to confirm they are exactly the same. If they are ever shown to be actually different, please feel free to update us.
5:12 - Dating myself here. I kid you not, I remember watching that, live as it happened. EDIT: Correction, I remember seeing it a little over a second after it happened.
It's very satisfying to watch these lectures, first bec they diminish ambiguity and increase scope of knowledge, and second is to follow the line of reasoning which makes things seem so easy, simple and self-evident that one may think "why haven't I thought of that"
I enjoy Dr Lincoln's videos. I'm a retired engineer and his videos get me thinking in new ways about the nature of things in our physical world that are often taken for granted. Thank you Dr Lincoln!
I love that kind of stuff happen in science: you take some idea, seemingly simple but if you think carefully and take it seriously you can sometimes go extremely far with it.
5:18 You mentioned they dropped a ball and feather in a vacuum chamber. And each hit at the same time. For a moment I wondered how they pumped out the gravity. It's fun finally having a manageable number of brain cells;but, I do hope the attrition stops now.
It's actually not uncommon to think about it this way, because air resistance isn't something that's taught in high school physics, so most people don't have a fundamental understanding of it. That's how terminal velocity works in an atmosphere - increasing your air resistance , or the drag coefficient, means that you fall more slowly. Once you think of things in terms of velocity, air resistance and gravitational mass, instead of merely falling, it makes perfect sense. You have no control over the gravitational mass because it is effectively constant, but you can affect air resistance. Parachutes increase drag, and your velocity with a parachute becomes slow and manageable. Cats approach their terminal velocity almost immediately when in freefall, and by spreading out their legs (their fur also increases drag) they can increase drag and use inertial mass to spin in any direction to arrive safely on the ground. They're already in freefall, so small movements in any direction will give them the ability to precisely spin in the direction they intend. Humans have a much higher terminal velocity and, as a result, impacts from a fall are fatal or seriously damaging. But we too can increase our drag when in freefall and stand a decent chance of survival.
Great presentation! Dr. Lincoln is deep in the details. Does mass affect gravity? My not so scientific answer: There are plenty of people who are curious about gravity, who, at the same time are totally fooled by mass. They think mass is a given. It’s so natural and predictable, isn’t it? I hope these people are surprised to find out that mass is normal matter’s passive resistance to any acceleration. Allow me the honor of explaining how this works. On the quantum level, every shred of normal matter is made of quarks that are moving at the local speed of light. The quarks remain localized because they have a relationship with the gluons that causes them to be contained. These quarks also have a relationship with the massless quarks of the galactic plasma, that are also moving at the speed of light. The contained quarks are accelerating in all directions at once. Any acceleration we contribute to a mass causes changes in its internal accelerations, which gets you an immediate gamma response from this matter, a passive resistive force we call mass. Can you measure mass without acceleration? Mass is normal matter’s resistance to kinetic acceleration. Glossing over all the details, gravity is normal matter’s response to chronic acceleration. It is simple. Do anything that changes the speed of light and matter will push itself around quite predictably. In order to have gravity there must be three details: 1. At least one mass. 2. Time dilation. 3. A gradient in the time dilation. Under these circumstances, the mass will push itself toward the local center of time dilation, where time is the slowest. I know, I know, this doesn’t sound like Isaac Newton at all.
This is interesting, it is almost like taking the probalistic model underpinning quantum theory and using the analogy of quantum exclusion with respect to lightspeed constancy and using that to explain the mechanics of inertial mass creation.
Are you saying, fundamentally, mass is simply the translation of the cosmological constant? It'd make sense after all - if time was 20% faster, objects would fall 20% faster. Considering all matter is restricted by gluons, which travel at the speed of light, they're restricted to the same level playing field.
@@RedNomster Gravity, mass, inertia, time dilation and an inertial frame of reference are all galactically defined and different in every galaxy. The filaments between galaxies have similar properties because they are the remnants of the previous generation of galaxies and still have some galactic plasma. I can't speak to the Cosmological Constant because I think nothing is universal.
LGB Gábor Lénárt it’s simple because it’s incomplete, you can see it from the note about being an hypothesis, or from the math , the constant does not to be one.
Actually, it would only be the ratios of the inertial to gravitational masses that would have to be the same. It is only by Ockhams Razor that we can assume this ratio to be 1.
Mass is the bending of space-time, right? So imagine every mass is at the bottom of a funnel (it's own gravity well in fact). Now when you try to push it, you're trying to push it out of it's own gravity well, hence inertia. Does that help?
@@Xeridanus I think you explain it well. Still, can you now go further and add relativity? Wouldn't you agree 'gravity well' metaphor fails when we add acceleration?
@@SFDestiny Oh that! I think that's a side effect of different reference frames. It doesn't really take more effort to accelerate an object once it's moving, that goes against relativity. You can confirm this by imagining it as the only object in the universe. What's actually happening is from an outside perspective, it seems to take more effort to accelerate the same amount. I think this is to do with the Doppler effect and bow wakes but with gravity waves/spacetime distortion. As an object accelerates the gravity waves/spacetime distortion in front bunch up like a bow wake, causing the (apparent) increased effort. But from the point of view of the object, the ripples are traveling away at the speed of light in all directions. The same thing happens to EM waves.
Now that you mentioned that Einstein took a simple concept of inertial mass is the same as gravitational mass to develop General Relativity, please make a video showing *how* he developed the theory of General Relativity. This video ends by saying what he did, but I want to know how he did it. How does a person take an idea so simple that nobody would doubt and turn it into a mind-blowing theory that up ends our notions about physics?
Einstein thought of a person in big box that had no idea where himself was. He then imagined that person falling with the box towards the ground and another accelerating in another box (think of your inertial resistance when you are accelerating or rotating in a car) and he wondered what would make a difference for them? How could they know whether they were falling or accelerating? That's basically, from my knowledge, how he found out that gravity and acceleration are the "same". He also thought the interaction between curvature of spacetime as a ant (mass) walking on a sheet of "wrapped" (not sure about this word) paper (spacetime curvature) and that the ant would be restricted to walk across the sheet on the little bumps and the (antonym of bumps) on it while it would itself provoke variation to some of those walking across it.
The experiment with a feather does not indicate inertial and gravitational mass equality. It just shows that the two parameters seem to have a fixed ratio. To check if that the ratio is equal to 1 is a bit harder to do.
A great video that allows to open our intuition and imagination to the possibility that gravitational mass could be different than inertial mass. It would be really amazing if we had found such an exceptional case in the entire universe.
Boy! It's amazing that the force required to move an object at the rate of acceleration of gravity is equal to the force of gravity! Who would have thought?
Going purely by the equation on 5:47, the argument that m1.gravitational=m1.inertial is not true. Mathematically, m1.grav / m1.inertial only has to be a fixed ratio for all m1 in order for that equation to be true. But I concede that you can always define or scale the gravitational constant G to incorporate this value so that in the ratio does become 1. Or maybe this should be an illuminating way to look at G itself, that it's the ratio of the two types of masses.
I'm a high school physics teacher. And thanks so much for this video! Awesome! This motion ties considerations from classical physics directly to modern physics.
Oke, I have to say that I did learn about the "different" kinds of mass and their equivalence (from PBS spacetime), but this video did make me appreciate it significance, as before I took it for granted. This is a very nice video you have here. Thank you
I totally appreciated the interesting coincidence of the inertial mass equating with the gravitational one. However, the authority of Einstein somehow prevented me from asking the question "why so". Thank you for bring this up. Looking forward to anyone possibly explaining this equality.
Who knew? Well most people would never consider this, as being out of the scope of our own day to day life. Although I hadn't considered mass much over the past 35 years, I found this a profound piece of information.
You thought there's only one type of mass. But there's actually two. They're equal thou, so it means there's actually only one type of mass. You can now be amazed. You're welcome.
Oh, there is more;) Also relativistic mass, he didn't mention here ("Is relativistic mass real" from Fermilab), or a nice approach to equivalent of mass and energy (PBS Space Time "The True Nature of Matter and Mass")
Recently speculated about inertia and gravity and their relationship with a friend, then this video came like a blessing. Thank you, and I hope you continue to upload more videos to come! They are very informative.
There is a slight but important error in this explanation. Objects accelerating at the same rate due to the gravitational field of another object implies that inertial and gravitational mass of the falling body are proportional not necessarily equal. That constant of proportionality can be set to unity with proper choice of units.
Zaid Khalil, I just had the same thought and commented to that effect. It seems like they assumed the two masses were equal and cancelled them in the equation. It just doesn't seem valid.
That's right, it is unity at normal speeds. The Voyager spacecraft flying at higher speeds over many years show that they are not as far out from the sun as they should be and galaxies flying away from us at huge speeds seem to have extra mass (dark mass) the charge mass is higher than inertial mass at those speeds, the ratio changes
At 5:40 actually it happens if every object has the same ratio of gravitational mass to inertial mass and this ratio could very well be different from 1 ;) it's just that because it has been observed that this ratio is constant, it's much more convenient to choose units in which this ratio is 1. It is the same as magnetic monopoles. The statement that there exist no magnetic monopoles (i.e. it has never been osberved) actually is that every particle has the same ratio of electric to magnetic charge and its convenient to "rotate" these charges to make the magnetic charge vanish.
Some theories predict the existence of magnetic monopoles (particles with a magnetic charge), but they were never observed. (Conversely, an electric monopole is simply a particle with an electric charge.)
What's really fun is if you take acceleration due to gravity as a given, then the "force" of gravity is just an observational effect based on that object's mass. Which seems to make a gravitation field into a distortion where the three spacial dimensions and the temporal dimension are no longer all orthagonal to each other as they should normally be. That is, an object that moves forward in time (read as: continues to exist) sees its spacial coordinates changed as time goes on in a way that isn't predicted simply by its initial velocity. I once read a suggestion that if you took a four-dimensional velocity vector of a given object (the fourth dimension being temporal, or "speed of aging") then as an object slows down, speeds up, or changes direction, the magnitude of this velocity vector remains constant. Presumably, this constant is equal to C, the understatedly-named "speed of light". I thought that was an interesting idea. That no matter how fast or how slow you're going, and no matter what direction you're traveling in, the overall magnitude of your velocity vector in spacetime is always C. You can never make the vector "longer" or "shorter". You can only change its direction. Now, the math on this is pretty simple. It's just the Pythagorean theorem with a couple dimensions added. Intermediate geometry. And it turns out, if you take the assertion from the above paragraph as a given, you can take your x, y, and z velocity, assume that the aggregate magnitude is C, and then solve for the unknown fourth dimension magnitude, the formula for this is precisely the time dilation formula. Maybe that's not supposed to be surprising. The time dilation formula might have arisen from this, or vice versa. But I didn't actually know the time dilation formula by heart when I heard this idea about the constant magnitude. I knew it existed. I knew that the basic idea was "the faster you go, the less you age", but I didn't know the exact numbers. I wanted to process this constant-magnitude idea, figure out what the formula _should_ be under that assumption, then compare it to the real thing without knowing the real thing ahead of time, and it totally worked out. And so I'm fairly confident that this same math can explain the way that gravitational fields affect the apparent passage of time. The only difference is that the temporal and three spacial dimensions are angled in such a way that they are no longer entirely independent of one another.
Now that surely blew my mind and I'd like to get more explanation on the connection with Einstein's General Relativity Theory! Mass is certainly an incredibly deep concept, I don't ever hope to understand it but it's fascinating to ponder.
Wait, you said that the different objects having the same acceleration shows that m,inertial = m,gravitational. But couldnt it be that every object just had the same ratio of m,inertial to m,gravitational?
@splitdog homee Ok, I thought that he meant m,inertial = k*m,gravitational for all objects we have tested yet, but that there could be some where it isnt. If he asked about m,inertial=k*m,gravitational for all objects then that is exactly what the video said to be the case.
@splitdog homee Ah, wait now I understood what he meant, my bad. So he means that inertial and gravitational mass are proportional (m,inertial = k*m,gravitational), but that k doesnt need to be 1. Ok, I dont know if I should delete my comment and make a new one, I think I will do that. Sorry for that misunderstanding.
So lets assume m,inertial and m,gravitational have a constant ratio, m,inertial/m,gravitational=k from our experiments. This means that we can write m,inertial/k=m.graviational. So in any formula that depends on m,gravitational we could simply write m,inertial/k. In many formuals you could even just put that factor k into an already existing constant like G for the gravitational force using newtons formula. In essence you can simplify this and only ever use m,inertial and because there is only one mass we use, we can call m,inertial simply m. The formulas are build around the known variables so it makes no difference.
Sir you are doing a great job. You provide authentic explanation to such things which our high schools textbooks just present as a fact. You really provide a source of learning for pondering minds like mine. I always wondered why gravitational mass and inertial mass had to be same. Thank you so much.
In my high school physics, I was taught about the two kinds of mass, and how the two are proved experimentally to have the same value. It is a bit of surprise to see this is being introduced here, along with videos about relativity.
Minor correction: Inertial mass is an inject's resistance to CHANGE in motion, or motion's vector more precisely, not resistance to motion. Much like self-inductance is resistance to CHANGE in electric current. Dr. Don!
Dr Lincoln, your video triggered electrifying thoughts in my brain: I'm still wavering thanks to them. Einstein's Theory of General Relativity truly deserve its special branch in the study of Physics: it will take me years just to understand its intricacies, yet I already can't help but marvel at how beautifully true it remains. The most successful theory of all times, indeed. How Einstein must have been thrilled when he observed these truths about our universe yet still remained down-to-earth, I wonder... More behind-the-scene revelations about common physics concepts? Yes! Please! :) Relatively yours, A Fermi-lagged viewer.
Ok, got it. Two types of mass. I understood it and am appreciative, but then the last line of the video you concluded by saying it all comes down to just one type of mass? What? I thought the whole point of the video was to show there are two types?
I think he means that the two masses are closely aligned because they produce the same effect, and I also think even physicists today do not even make a big distinction when doing calculations , because it would be meaningless to do so?
Inertial mass is the resistance to a force, gravitational mass is the "capacity" to generate a gravity field, but they are equal in the end, they aren't the same thing, just equal. this means that the "capacity" to generate a gravity field is equal to the resistance that an object opposes to a force.
It might not surprise you anymore, because it's deeply embedded in your intuition and we both call them "mass". The connection between gravity and inertia isn't that obvious though. Think about it, why does the force of gravity happen to depend on inertial mass, yet the electromagnetic force depend on some other metric of the object?
Don Lincoln could have added that in general relativity gravitation is not a real force but a pseudo force in space-time (similar to e.g. the centrifugal or other inertial pseudo forces accelerated observers may experience), and that the effect of "gravity" on objects (whether they are in free fall or not) is just a manifestation of the inertia of objects moving through curved space-time. In this framework, gravitational mass IS inertial mass.
@@WilcoVerhoef ~ Electromagnetic force is different because there are positive and negative charges, so electrons can change the charge of an object, but gravity has no opposite, so there's no way to alter gravity except by adding or subtracting mass.
@@FrankCoffman Even if there were no opposite, the electrical force is still dependent on a property other than the amount of material in an object in order for it to work. The force of buoyancy for instance, can only happen in the direction opposite gravity, and comes in proportion to an object's volume. You cannot have negative volume, such that the force of buoyancy pushes an object down, instead of pushing an object upward. But unlike gravity, the property of volume that makes an object participate in the force of buoyancy, is independent of an object's mass. Sure, there is some correlation, but you can modify how dense or sparse the object is, in order to independently control the force of buoyancy from the object's mass. We can't do the same with gravity. There is no known way to make an object have a greater ratio between how much it participates in gravity and how much it resists a change in state of motion.
Einstein said that "gravity and inertia are identical in nature", not just gravitational and inertial mass. Putting the qualifying subscript to distinguish inertial mass from gravitational mass in the equations wrong. It is based on incorrect preconceived notions that should have been cleared up over 100 years ago when Einstein informed us of this.
I didn't know that physics is everything, but I 'm beginning to lean in that direction. The fact that inertial mass and gravitational mass are the same, sounds very interesting.
I don't understand the math, even simple Algebra like this because I was a fool and made no effort in school, but I really appreciate that these videos exist for those wiser than me. I feel like showing these to kids in middle school would strongly counter the attitude "how's this stuff going to be useful to ME?" Had I known algebra was so useful to understanding incredibly interesting stuff like physics and the universe, I am sure I'd have made an effort instead of doing the bare minimum and immediately forgetting it all.
as an electrical engineer I listen to your videos quite regulary to learn more about physics around and ask myself , why did I study electronics? Tnx for sharing!
This concept was just amazing. Till now I was getting my mind blown by all the concepts I didn't know. But this one blew my mind by something I thought I knew and understood pretty well. It's like finding a secret room in a house that you have lived in for years!
I just didn't understand why inertial and gravitational mass are necessarily equal. I mean, can't they just be proportional? I don't know a lot about Newton's and other physicist's experience to find the constant G. But couldn't we readjust G to make it work. For example, let's suppose mG = mI * 2. So mG/mI = 2. So, in order for the expression F = m1G*m2G/m1Ir² To still be true, we would just need to adjust G to be half of its current value. Basically, cant both masses just be proportional?
Newton's law of gravity doesn't contain a m-squared element; it contains an element of "mass of the first object" times "mass of the second object". If we multiply the gravitational mass of each object by 2, and divide the gravitational constant by 4, the force remains the same; and if we do this while keeping the inertial mass the same, the acceleration remains the same. (In other words, we can assume that gravitational mass is not the same as inertial mass, as long as the ratio of the two is constant for all objects, and get a theory which is mathematically equivalent to Newtonian mechanics.)
Yes, you could assign the constant ratio of M[grav]/M[in] to be anything you like, including units. This would carry with it, a counterbalancing change in the value and units of G. So there being no compelling reason for any particular value for such a ratio, the easiest choice is, just make it = 1.
True but the point is that the ratio of the gravitational charge to the inertial mass is a constant for all objects. This is not the case for the ratio of the electric charge to the inertial mass between different objects. For example, an electron has a different electric charge to inertial mass ratio compared to a proton. It's possible to add a certain amount of inertial mass to an object without adding any net electric charge. However, whenever a certain amount of inertial mass is added to an object its gravitational charge always increases in direct proportion. We can choose the value of this ratio to be whatever we wish, so long as we invent a system of units to distinguish between gravitational charge and inertial mass. The value of G will take on different values depending on the value of the gravitational to inertial mass ratio that we have chosen in our new system of units. We already do something similar when it comes to measuring distances and time intervals. We use one unit to measure distances and another unit to measure time intervals. We could easily use the same unit for both distances and time intervals.
This is a great theoretical (via equations) demonstration of the difference between gravitational and inertial mass. I understood the difference before, but now I can point to the two equations which involve them and how they connect. Thanks!
School teachers often use horrible explainations. They’re probably all wrong. These 10 minutes were amazing. Next video should be why some materials are opaque and others aren’t.
Here is a little extra for those who would like to know. The moment of inertia is like mass in the sense that it resists changes in motion. However, the type of motion that the moment of inertia resists is rotational motion.
50 years ago in school I asked my physics teacher why he sets both masses equal. If there is a "m" in the inertial law and a "m" in the gravitational law those "m" must not be the same. Nice to hear about that question today. My question today: is the Higgs field only about the inertial law? The light which is not affected by Higgs is affected by gravity.
i was going to say hes worth more than that and raise the stakes to cheetos... but then i realized dog biscuits are worth more. So instead im going to double down and boost his worth to seasoned boneless pork chops.
From our perspective things seem to fall to earth . They also seem to accelerate when dropped. Finding a frame of reference that clearly explains this action would give way to understanding what gravity is. Thanks for the vid.
Inertial mass happens in a Catholic church and gravitational mass happens in a Lutheran church. Both involve very weighty subjects and require the "God particle." If you pray hard enough during mass then God will reach across the universe and bless you. This is sometimes referred to as "spooky action at a distance." Until the day you die you exist in a "superposition" of grace and damnation. After death, you collapse into a particle which will exist either in heaven or hell. This is called "conservation of souls." Hope that clarifies matter(s) for you, Burt. i wasn't planning to go on so long, but I developed a lot of momentum.
burt591 Inertial mass is how much an object resists being moved, or how much energy you have to expend to accelerate it a given amount. The more massive the object, the more energy you need to accelerate it. Gravitational mass is the force with which the object attracts other objects, and is attracted by them, through gravity. More massive objects (such as the earth) attract others more strongly than smaller ones (such as the moon).
inertial mass is what causes: F=ma (Newtons 2nd law) gravitational mass is what causes F = Gm1m2/r² Experiments show that inertial mass = gravitational mass = mass, so these two kinds of masses are one and the same. That's not really surprising, but according to our understanding it doesn't necessarily have to be that way (although it, for whatever reason, is).
Ted L. Okay, but I guess that this leaves the Calvinist in either a vacuum or a black hole, depending upon his predestination, and the fact that Calvinist teachings exclude the notion of mass
Simply put... inertial mass the resistance to change in motion & determines how much energy is needed to change an object's motion. Gravitational mass... effects how severely space is warped & the density of an object.
That Galileo dropped weights from the leaning tower of Pisa comes from a biography written by a man who had been his secretary for many years (though after he left Pisa). We have a statement from Galileo's own hand that he dropped weights from "a high place" while he lived Pisa.
it won't work. By symmetry. See the issue from the perspective of the particle and the ratio for the earth will be G too. You get a G^2 term. Repeat for multiple objects and you get a theory that does not work as expected. Finaly it has been messure to a high presition. Also Clocks do slow in grabittional feels, we have messure that with atomic clocks. So it looks correct to a high degree of presition.
The point is that the ratio of the gravitational charge to the inertial mass is a constant for all objects. This is not the case for the ratio of the electric charge to the inertial mass between different objects. For example, an electron has a different electric charge to inertial mass ratio compared to a proton. It's possible to add a certain amount of inertial mass to an object without adding any net electric charge. However, whenever a certain amount of inertial mass is added to an object its gravitational charge always increases in direct proportion. We can choose the value of this ratio to be whatever we wish, so long as we invent a system of units to distinguish between gravitational charge and inertial mass. The value of G will take on different values depending on the value of the gravitational to inertial mass ratio that we have chosen in our new system of units. We already do something similar when it comes to measuring distances and time intervals. We use one unit to measure distances and another unit to measure time intervals. We could easily use the same unit for both distances and time intervals.
“We’ve all been indoctrinated in the idea that there is only one kind of mass “ The textbook of my high school physics stated that there are the inertial mass and the gravitational mass, and the equivalence of the two cannot be taken for granted.
So to summarise: Thanks to Einstein starting with a hypothesis, working through relativity, we now know that mass is mass... Where do I apply for a study grant?
@Kungpao Kitty I actually agree with the sentiment. Dr. Lincoln thinks these videos are about him, not physics. I just unsubbed because I can't take his ego and lack of clarity anymore.
I do not comprehend this at all. True story: When I was five I understood that things were made of atoms. One day my older brother asked, "Will a 10lb steel ball fall faster than a 5lb steel ball?" (he was always trying to trick/teach something), I took a moment, imagined each atom falling, realized that the heavy thing had more atoms but individually they would behave the same as the atoms in the lighter thing and said "no". At the age of five (still blows his mind). So, I do not lack for intuition about these things but I absolutely do not 'get' the difference between gravitational mass and inertial mass. The speed something falls will be resisted by its inertial mass or it would fall at the speed of light with any arbitrary force accelerating it (small or large). I don't comprehend how a universe could possibly exist (this one or any other one) if gravitational and inertial mass are not the same thing. I do not mean the same value, I mean the same thing. That's how it fits in my head but I'd be thrilled if someone could separate those two things in a way that I 'get it'. This video (and I love these Fermilab videos) did not do that. Didn't even scratch it. (Another of his test/tricks was this (when I was 9): "If I tied a rope to each end of a spring scale, gave one end to you, and you pull 10lbs and I pull 10lbs, what does the scale show?" [Hint: (that he didn't give) Think of a fence post.]
He said that was the opinion of most physicists, but that there are still some that disagree. If the change in momentum at relativistic speed is not due to a change in mass, but to the Lorenz factor gamma, that still leaves open the question of what physical interpretation to give gamma, which he didn't address in that video.
1. Ditto ScienceNinjaDude. Plus which, accepting "relativistic mass" would require different masses for the same object, in different equations! The usual rel. mass derived from rel. momentum, doesn't work for, say, rel. kinetic energy, and so on. 2. Well, for one thing, general relativity would be out the window, because it absolutely hinges on that ratio being constant.
This is a very cool video channel. I originally found them looking for videos on QCD. They do a good job of explaining it and going deep enough to satisfy me but not over my head
Doctor Lincoln, I've watched many of your lectures. You are indeed a remarkable teacher. Thank you for showing all of us that physics is for everybody!! Well done!
To piggy back on this top comment, I would like to mention that the equivalence principle is NOT Einstein's idea. As Dr. Lincoln himself states, this idea dates back to Galileo. But he, like everyone else, attributes this to Einstein falsely. Furthermore there are many issues with the equivalence principle in general relativity that is not often discussed among the public but has been extensively discussed among general relativity experts. Einstein changed the requirements of the equivalence principle at least twice and deluded himself into believing it is a secondary consequence of general covariance. His early formulation of the equivalence principle (before 1933) was incorrect. Einstein did not understand "his" theory of general relativity because all the dirty work was formulated mathematically by Grossmann and Hilbert.
You forgot to mention Galileo's superb 'reductio ad absurdum' regarding this matter.
Let's suppose heavier objects fall faster than light objects.
Imagine two heavy objects (A and B), one weighs 2 pounds (A), and one weighs 1 pound (B). Imagine connecting these two objects with a string. if heavier objects fall faster than light objects, then the lighter object B, will act as a drag on the heavier object when we drop our tethered weights off a tower. So A will fall slower than it would if untied to B.
But A and B tied together weigh more, so the combined weights should actually fall faster than the heavier weight alone.
So the combined objects should fall both slower, and faster, than the heavier object (A) alone.
That's a manifest contradiction. So we now know that our initial premise (heavier things fall faster than light things) is manifestly wrong. It has to be false. And we don't even have to leave the house to drop weights off a tower to prove it.
I love this! Thank you made my day :)
bravo
This is just wow man. Thanks for this
Except that someone could probably come up with a definition of "object" involving rigidity and mass distribution that would disqualify the two balls and string from being treated as a single one. Anyway, the fact that they do fall at the same rate shows the two types of mass are the same, no need to invoke GR.
Ni there's no contradiction, just a missunderstanding of how gravity on your side.
Gravity is due to mass, but density does matter because gravity also depends on distance. A more dense object of a given mass is smaller, so you can get closer to its centre of mass and experience a stronger gravitational force.
Second, density is also related to mass which means that an object with more density needs a smaller volume to have the same weight as an object with less density. Gravity is dependant on mass and the distance between the two objects. ... However, just going purely on the equation, gravity has no dependence on density.
An object with twice as much mass will exert twice as much gravitational pull on other objects. The gravitational force increases as the size of an object increases. On the other hand, the strength of gravity is inversely related to the square of the distance between two objects.
The weight of an object is the force of gravity on the object and may be defined as the mass times the acceleration of gravity, w = mg. Since the weight is a force, its SI unit is the newton. Density is mass/volume.
The density of water is 1000 kg/cubic meters at 4 Celsius. In physics, the weight of the substance differs from its mass. The weight is the gravitational force that pulls any object to Earth. The specific weight corresponds to the weight per unit of the volume and can be calculated from the specific gravity.
My Physics master was a tool.
This video explained so much which was easily understood.
Thank you for putting back my faith in myself
Take something that everyone knows, what is essentially, "common sense" and show us just how mind blowingly awesome it actually is.
You'd think by now, having seen so many of your videos that it would be expected, but you just keep surprising me.
just when you thought you were beginning to understand some basic concepts of the universe after thirty years of teaching physics, someone comes along and in a few short videos completely opens up a whole new way of seeing things. absolutely stunning. I will definitely be including these 10mins video at the end of each lesson.
0:56 This isn't about Einstein's theory of relativity or anything like that... 7:15 wild Einstein appears
Dont think you understand what he meant
@@madhunayak165 same to ya
Technically gravitational mass and inertial mass could be perfectly linearly related by Mi =kMg. For example, if you use a gravitational constant that is 4 times larger, then you would have gravitational mass 2 times smaller than the inertial mass, and all the equations would still work out (k=2). If we just set the constant to 1 it works out that they are equal, but there is nothing you can derive that says it is 1. It's an axiom.
they should include your comment in the video.
@matttonkthetank5619 nice catch! I came here to make a similar comment. So, the observation that all of the objects we try experience identical acceleration in a gravitational field only shows that Mi/Mg is constant, not necessarily 1. And I'm also tempted to ask for how many kinds of objects and with what precision we've verified this. Truly, for experiments like Galileo's and Cox's, the answers would have to be "only a few" and "not with very much precision". But I guess people who build rockets have by now found it to be reliably enough constant that their rockets have behaved very precisely, regardless of payload contents. For example, being able to slingshot from one planet to another seems like a very precise activity.
And I agree with you. But the consequences of this could be very large-scale. Does anyone know if there are theories in which inertial and gravitational mass are not equal, but only proportional?
@@faberant I'm not qualified to answer that question. But in the video, Dr. Lincoln says that Einstein set the two quantities identical in his General Relativity derivations (I have no idea where that came in). If they were not identical, but only proportional, perhaps such a change to one of his assumptions would have forced differences in that theory. And perhaps such an alternative theory would give different predictions than G.R. which one could then test, or maybe some such predictions have already been tested.
yes, i thought the same, like why G is the way it's calculated? it's not even derived from some unification of forces?
I am not a physicist, just passionate about physics. But I do understand that what Dr. Lincoln is trying to tell us in this video, and which is actually mind-blowing, is that at the end of the day, we still don’t know why objects fall. Because of the gravity say physics books since Newton. But what the heck is gravity? It should be an electromagnetic charge, but it doesn’t behave as such. Because then lighter objects, not heavier ones, should fall faster. Along comes Einstein and says that there is no such thing as gravity (makes sense), and things fall because of the curvature of the space-time fabric. So which one is it then: gravity or space-time curvature? Physics still doesn’t know the answer, and this is really mind-blowing.
him: you thought there was only one type of mass
me: yeah
him: but there's actually two
me: mmmh
him: but actually it's just one
me: AH! I KNEW IT!
Yeah... Kinda pointless.
X and Y are variables and just because they're equal doesn't mean they're the same variable. The distiction is important for understanding and in the case that our fundementals change. Which it may in the pursuit of a unifying theory of quantum and gravity.
@@lazycouch1 lol I understand the difference, I was making a joke on it
@@BigLiftsITA Good joke
@@lazycouch1 Just because you use different variables doesn't mean the quantities represented are different. As far as we are able to confirm they are exactly the same. If they are ever shown to be actually different, please feel free to update us.
the ease and intuition with which Dr Lincoln describes the concepts is really amazing. Thank you for the time and effort @fermilab and Dr Lincoln.
5:12 - Dating myself here. I kid you not, I remember watching that, live as it happened.
EDIT: Correction, I remember seeing it a little over a second after it happened.
i am picturing some alien archaeologist finding that feather next to the gear left on the moon after humans are extinct and assuming we had feathers.
@@kevint1910 LOL this comment made my day😂😂😂😂
I often date myself. But that's okay. I'm a cheap date and treat myself well.
@@jeffreyquinn3820 lol
Dating yourself? Kinda lonely, innit?
It's very satisfying to watch these lectures, first bec they diminish ambiguity and increase scope of knowledge, and second is to follow the line of reasoning which makes things seem so easy, simple and self-evident that one may think "why haven't I thought of that"
I enjoy Dr Lincoln's videos. I'm a retired engineer and his videos get me thinking in new ways about the nature of things in our physical world that are often taken for granted. Thank you Dr Lincoln!
I love that kind of stuff happen in science: you take some idea, seemingly simple but if you think carefully and take it seriously you can sometimes go extremely far with it.
5:18 You mentioned they dropped a ball and feather in a vacuum chamber. And each hit at the same time.
For a moment I wondered how they pumped out the gravity.
It's fun finally having a manageable number of brain cells;but, I do hope the attrition stops now.
It's actually not uncommon to think about it this way, because air resistance isn't something that's taught in high school physics, so most people don't have a fundamental understanding of it. That's how terminal velocity works in an atmosphere - increasing your air resistance , or the drag coefficient, means that you fall more slowly.
Once you think of things in terms of velocity, air resistance and gravitational mass, instead of merely falling, it makes perfect sense. You have no control over the gravitational mass because it is effectively constant, but you can affect air resistance.
Parachutes increase drag, and your velocity with a parachute becomes slow and manageable. Cats approach their terminal velocity almost immediately when in freefall, and by spreading out their legs (their fur also increases drag) they can increase drag and use inertial mass to spin in any direction to arrive safely on the ground. They're already in freefall, so small movements in any direction will give them the ability to precisely spin in the direction they intend.
Humans have a much higher terminal velocity and, as a result, impacts from a fall are fatal or seriously damaging. But we too can increase our drag when in freefall and stand a decent chance of survival.
Great presentation! Dr. Lincoln is deep in the details. Does mass affect gravity? My not so scientific answer:
There are plenty of people who are curious about gravity, who, at the same time are totally fooled by mass. They think mass is a given. It’s so natural and predictable, isn’t it? I hope these people are surprised to find out that mass is normal matter’s passive resistance to any acceleration.
Allow me the honor of explaining how this works. On the quantum level, every shred of normal matter is made of quarks that are moving at the local speed of light. The quarks remain localized because they have a relationship with the gluons that causes them to be contained. These quarks also have a relationship with the massless quarks of the galactic plasma, that are also moving at the speed of light. The contained quarks are accelerating in all directions at once. Any acceleration we contribute to a mass causes changes in its internal accelerations, which gets you an immediate gamma response from this matter, a passive resistive force we call mass. Can you measure mass without acceleration? Mass is normal matter’s resistance to kinetic acceleration.
Glossing over all the details, gravity is normal matter’s response to chronic acceleration. It is simple. Do anything that changes the speed of light and matter will push itself around quite predictably.
In order to have gravity there must be three details: 1. At least one mass. 2. Time dilation. 3. A gradient in the time dilation.
Under these circumstances, the mass will push itself toward the local center of time dilation, where time is the slowest.
I know, I know, this doesn’t sound like Isaac Newton at all.
This is interesting, it is almost like taking the probalistic model underpinning quantum theory and using the analogy of quantum exclusion with respect to lightspeed constancy and using that to explain the mechanics of inertial mass creation.
Woah
Are you saying, fundamentally, mass is simply the translation of the cosmological constant? It'd make sense after all - if time was 20% faster, objects would fall 20% faster. Considering all matter is restricted by gluons, which travel at the speed of light, they're restricted to the same level playing field.
@@RedNomster Gravity, mass, inertia, time dilation and an inertial frame of reference are all galactically defined and different in every galaxy. The filaments between galaxies have similar properties because they are the remnants of the previous generation of galaxies and still have some galactic plasma. I can't speak to the Cosmological Constant because I think nothing is universal.
I am officially NOT smarter after watching this
Wow, very nice explanation :) I've learnt these way too many years ago. I just wish I could see this video when I had to learn about this ...
LGB Gábor Lénárt it’s simple because it’s incomplete, you can see it from the note about being an hypothesis, or from the math , the constant does not to be one.
Yeah. No shit.
thank you for making these videos. I love watching them because I learn something new every time. Very informative and easy to understand.
Actually, it would only be the ratios of the inertial to gravitational masses that would have to be the same. It is only by Ockhams Razor that we can assume this ratio to be 1.
Brilliant, clear and mostly neccesary explanation, Dr. Lincoln!
I am not really into physics. But this video really made the concept of mass more clearer and obviously, blew my head as well! So, thank you.
"gravitational mass is like the charge of gravity" - what a great way to phrase it! Thanks for your clear, instructive videos!
This video is not just good because of it's contents, but marvelous because of Dr. Don Lincoln's hand gestures!
That gravitational mass and inertial mass are equal has always been a mystery to me. Could you go deeper in another video?
Mass is the bending of space-time, right? So imagine every mass is at the bottom of a funnel (it's own gravity well in fact). Now when you try to push it, you're trying to push it out of it's own gravity well, hence inertia. Does that help?
@@Xeridanus I think you explain it well. Still, can you now go further and add relativity? Wouldn't you agree 'gravity well' metaphor fails when we add acceleration?
@@SFDestiny The gravity well metaphor is explaining relativity. How does it fail with acceleration though? I thought I was describing exactly that.
@@Xeridanus maybe I simply don't grok it yet. What does it mean in your metaphor that a well gets deeper as it accelerates?
@@SFDestiny Oh that! I think that's a side effect of different reference frames. It doesn't really take more effort to accelerate an object once it's moving, that goes against relativity. You can confirm this by imagining it as the only object in the universe. What's actually happening is from an outside perspective, it seems to take more effort to accelerate the same amount. I think this is to do with the Doppler effect and bow wakes but with gravity waves/spacetime distortion. As an object accelerates the gravity waves/spacetime distortion in front bunch up like a bow wake, causing the (apparent) increased effort. But from the point of view of the object, the ripples are traveling away at the speed of light in all directions. The same thing happens to EM waves.
I love these videos because you make everything easy to understand, but you don’t shy away from using equations to prove your point. Well done!
Now that you mentioned that Einstein took a simple concept of inertial mass is the same as gravitational mass to develop General Relativity, please make a video showing *how* he developed the theory of General Relativity. This video ends by saying what he did, but I want to know how he did it. How does a person take an idea so simple that nobody would doubt and turn it into a mind-blowing theory that up ends our notions about physics?
Einstein thought of a person in big box that had no idea where himself was. He then imagined that person falling with the box towards the ground and another accelerating in another box (think of your inertial resistance when you are accelerating or rotating in a car) and he wondered what would make a difference for them? How could they know whether they were falling or accelerating? That's basically, from my knowledge, how he found out that gravity and acceleration are the "same". He also thought the interaction between curvature of spacetime as a ant (mass) walking on a sheet of "wrapped" (not sure about this word) paper (spacetime curvature) and that the ant would be restricted to walk across the sheet on the little bumps and the (antonym of bumps) on it while it would itself provoke variation to some of those walking across it.
I'd love to see a video like this as well!
The Equivalence principle.
If it looks like a duck, walks like a duck, quacks like a duck ... you know.
It was just a postulate based upon experiment. You can google this as Etovos Experiments..
Rich Sposato Geometry and Calculus. That's how you can derive the whole equation.
The experiment with a feather does not indicate inertial and gravitational mass equality. It just shows that the two parameters seem to have a fixed ratio. To check if that the ratio is equal to 1 is a bit harder to do.
Fantastic videos can't get enough of them. I don't fully understand everything that is said but drop by drop it's turning into a lake. Thanks
A great video that allows to open our intuition and imagination to the possibility that gravitational mass could be different than inertial mass. It would be really amazing if we had found such an exceptional case in the entire universe.
Boy! It's amazing that the force required to move an object at the rate of acceleration of gravity is equal to the force of gravity! Who would have thought?
Wooooooooosh bro
This is the reason that at age 62 I am restarting at basic arithmetic with my - so far uncomprehending eyes - fixed on calculus. Thank you Doctor!
Going purely by the equation on 5:47, the argument that m1.gravitational=m1.inertial is not true. Mathematically, m1.grav / m1.inertial only has to be a fixed ratio for all m1 in order for that equation to be true.
But I concede that you can always define or scale the gravitational constant G to incorporate this value so that in the ratio does become 1. Or maybe this should be an illuminating way to look at G itself, that it's the ratio of the two types of masses.
Exactly what I was thinking! I don't understand why he said that.
Or that G represents the effect of the bending of space & time caused by mass. I know I learned something from all those science fiction books.
I'm a high school physics teacher. And thanks so much for this video! Awesome! This motion ties considerations from classical physics directly to modern physics.
Oke, I have to say that I did learn about the "different" kinds of mass and their equivalence (from PBS spacetime), but this video did make me appreciate it significance, as before I took it for granted. This is a very nice video you have here. Thank you
UMMMM, AND WHY ARENT YOU FEEDING THE HOMELESS????
I've been watching for a while and you make things way more simple than a seminar. Bless you!
Mind blown. More, please!
most of what this guy says kind of goes over my head but hes a cool guy and really loves what hes shareing. i like his videos. keep it up man.
Thanks, Doc Don, good explanation as always. Also, cool T-shirt (as always). Have a nice saturnalia!
I never observed this ..and it never rang a bell in my head until now thank you Dr.Don Lincoln
Great video please continue this types of video about unappreciated pieces of physics
I totally appreciated the interesting coincidence of the inertial mass equating with the gravitational one. However, the authority of Einstein somehow prevented me from asking the question "why so". Thank you for bring this up. Looking forward to anyone possibly explaining this equality.
Mindblowing indeed. Even if not particularly new. Reminds me of struggling through Steven Weinbergs great Book “Gravitation and Cosmology”
Who knew? Well most people would never consider this, as being out of the scope of our own day to day life.
Although I hadn't considered mass much over the past 35 years, I found this a profound piece of information.
You thought there's only one type of mass. But there's actually two. They're equal thou, so it means there's actually only one type of mass.
You can now be amazed.
You're welcome.
Oh, there is more;) Also relativistic mass, he didn't mention here ("Is relativistic mass real" from Fermilab), or a nice approach to equivalent of mass and energy (PBS Space Time "The True Nature of Matter and Mass")
May be both mass are same but in a different form of energy
Ok. That blew my head!
Recently speculated about inertia and gravity and their relationship with a friend, then this video came like a blessing. Thank you, and I hope you continue to upload more videos to come! They are very informative.
There is a slight but important error in this explanation. Objects accelerating at the same rate due to the gravitational field of another object implies that inertial and gravitational mass of the falling body are proportional not necessarily equal. That constant of proportionality can be set to unity with proper choice of units.
No, it doesn't.
The other mass term is what causes the gravitational field of the object that the falling bodies are attracted to.
Zaid Khalil, I just had the same thought and commented to that effect. It seems like they assumed the two masses were equal and cancelled them in the equation. It just doesn't seem valid.
That does not mater because then the value of G would be ajusted
That's right, it is unity at normal speeds. The Voyager spacecraft flying at higher speeds over many years show that they are not as far out from the sun as they should be and galaxies flying away from us at huge speeds seem to have extra mass (dark mass) the charge mass is higher than inertial mass at those speeds, the ratio changes
Just found this youtube channel. Thanks Fermilab and Don this is just what we need more of. Science majors is the way forward.
At 5:40 actually it happens if every object has the same ratio of gravitational mass to inertial mass and this ratio could very well be different from 1 ;) it's just that because it has been observed that this ratio is constant, it's much more convenient to choose units in which this ratio is 1. It is the same as magnetic monopoles. The statement that there exist no magnetic monopoles (i.e. it has never been osberved) actually is that every particle has the same ratio of electric to magnetic charge and its convenient to "rotate" these charges to make the magnetic charge vanish.
actually magnetic monopoles do exist.
Some theories predict the existence of magnetic monopoles (particles with a magnetic charge), but they were never observed. (Conversely, an electric monopole is simply a particle with an electric charge.)
Can you elaborate on the last sentence?
I think he is talking about only one object inertial and gravitational mass
What's really fun is if you take acceleration due to gravity as a given, then the "force" of gravity is just an observational effect based on that object's mass. Which seems to make a gravitation field into a distortion where the three spacial dimensions and the temporal dimension are no longer all orthagonal to each other as they should normally be. That is, an object that moves forward in time (read as: continues to exist) sees its spacial coordinates changed as time goes on in a way that isn't predicted simply by its initial velocity.
I once read a suggestion that if you took a four-dimensional velocity vector of a given object (the fourth dimension being temporal, or "speed of aging") then as an object slows down, speeds up, or changes direction, the magnitude of this velocity vector remains constant. Presumably, this constant is equal to C, the understatedly-named "speed of light". I thought that was an interesting idea. That no matter how fast or how slow you're going, and no matter what direction you're traveling in, the overall magnitude of your velocity vector in spacetime is always C. You can never make the vector "longer" or "shorter". You can only change its direction.
Now, the math on this is pretty simple. It's just the Pythagorean theorem with a couple dimensions added. Intermediate geometry. And it turns out, if you take the assertion from the above paragraph as a given, you can take your x, y, and z velocity, assume that the aggregate magnitude is C, and then solve for the unknown fourth dimension magnitude, the formula for this is precisely the time dilation formula.
Maybe that's not supposed to be surprising. The time dilation formula might have arisen from this, or vice versa. But I didn't actually know the time dilation formula by heart when I heard this idea about the constant magnitude. I knew it existed. I knew that the basic idea was "the faster you go, the less you age", but I didn't know the exact numbers. I wanted to process this constant-magnitude idea, figure out what the formula _should_ be under that assumption, then compare it to the real thing without knowing the real thing ahead of time, and it totally worked out.
And so I'm fairly confident that this same math can explain the way that gravitational fields affect the apparent passage of time. The only difference is that the temporal and three spacial dimensions are angled in such a way that they are no longer entirely independent of one another.
it would be awesome to have a playlist, organized in the order to watch
I fully subscribe to your suggestion :)
Now that surely blew my mind and I'd like to get more explanation on the connection with Einstein's General Relativity Theory!
Mass is certainly an incredibly deep concept, I don't ever hope to understand it but it's fascinating to ponder.
Wait, you said that the different objects having the same acceleration shows that m,inertial = m,gravitational. But couldnt it be that every object just had the same ratio of m,inertial to m,gravitational?
@splitdog homee Ok, I thought that he meant m,inertial = k*m,gravitational for all objects we have tested yet, but that there could be some where it isnt. If he asked about m,inertial=k*m,gravitational for all objects then that is exactly what the video said to be the case.
@splitdog homee Ah, wait now I understood what he meant, my bad. So he means that inertial and gravitational mass are proportional (m,inertial = k*m,gravitational), but that k doesnt need to be 1. Ok, I dont know if I should delete my comment and make a new one, I think I will do that. Sorry for that misunderstanding.
So lets assume m,inertial and m,gravitational have a constant ratio, m,inertial/m,gravitational=k from our experiments. This means that we can write m,inertial/k=m.graviational. So in any formula that depends on m,gravitational we could simply write m,inertial/k. In many formuals you could even just put that factor k into an already existing constant like G for the gravitational force using newtons formula. In essence you can simplify this and only ever use m,inertial and because there is only one mass we use, we can call m,inertial simply m. The formulas are build around the known variables so it makes no difference.
This is why there are published textbooks and refereed journals. Some errors in here combined with a convincing delivery. Dangerous.
Andres Rosales Exactly, I thought the same
I love you Fermilab
Sir you are doing a great job. You provide authentic explanation to such things which our high schools textbooks just present as a fact. You really provide a source of learning for pondering minds like mine. I always wondered why gravitational mass and inertial mass had to be same. Thank you so much.
In my high school physics, I was taught about the two kinds of mass, and how the two are proved experimentally to have the same value. It is a bit of surprise to see this is being introduced here, along with videos about relativity.
Minor correction: Inertial mass is an inject's resistance to CHANGE in motion, or motion's vector more precisely, not resistance to motion. Much like self-inductance is resistance to CHANGE in electric current. Dr. Don!
4:56
Why do you use a animation where the small ball is falling faster while saying that both fall with the same speed?
It could confuse some.
Dude things are not perfect. Whose getting confused. I get your point but it's really doesn't matter, his explaining it with speech. No offense
Dr Lincoln, your video triggered electrifying thoughts in my brain: I'm still wavering thanks to them.
Einstein's Theory of General Relativity truly deserve its special branch in the study of Physics: it will take me years just to understand its intricacies, yet I already can't help but marvel at how beautifully true it remains.
The most successful theory of all times, indeed. How Einstein must have been thrilled when he observed these truths about our universe yet still remained down-to-earth, I wonder...
More behind-the-scene revelations about common physics concepts? Yes! Please! :)
Relatively yours,
A Fermi-lagged viewer.
Ok, got it. Two types of mass. I understood it and am appreciative, but then the last line of the video you concluded by saying it all comes down to just one type of mass? What? I thought the whole point of the video was to show there are two types?
I think he means that the two masses are closely aligned because they produce the same effect, and I also think even physicists today do not even make a big distinction when doing calculations , because it would be meaningless to do so?
Inertial mass is the resistance to a force, gravitational mass is the "capacity" to generate a gravity field, but they are equal in the end, they aren't the same thing, just equal. this means that the "capacity" to generate a gravity field is equal to the resistance that an object opposes to a force.
You mean why I had to go every Sunday to this thing that ate all my procrastination study time?
I dont get why interial mass and gravitational mass being the same is so amazing
It might not surprise you anymore, because it's deeply embedded in your intuition and we both call them "mass".
The connection between gravity and inertia isn't that obvious though. Think about it, why does the force of gravity happen to depend on inertial mass, yet the electromagnetic force depend on some other metric of the object?
Don Lincoln could have added that in general relativity gravitation is not a real force but a pseudo force in space-time (similar to e.g. the centrifugal or other inertial pseudo forces accelerated observers may experience), and that the effect of "gravity" on objects (whether they are in free fall or not) is just a manifestation of the inertia of objects moving through curved space-time. In this framework, gravitational mass IS inertial mass.
@@WilcoVerhoef ~ Electromagnetic force is different because there are positive and negative charges, so electrons can change the charge of an object, but gravity has no opposite, so there's no way to alter gravity except by adding or subtracting mass.
@@FrankCoffman Even if there were no opposite, the electrical force is still dependent on a property other than the amount of material in an object in order for it to work. The force of buoyancy for instance, can only happen in the direction opposite gravity, and comes in proportion to an object's volume. You cannot have negative volume, such that the force of buoyancy pushes an object down, instead of pushing an object upward. But unlike gravity, the property of volume that makes an object participate in the force of buoyancy, is independent of an object's mass. Sure, there is some correlation, but you can modify how dense or sparse the object is, in order to independently control the force of buoyancy from the object's mass.
We can't do the same with gravity. There is no known way to make an object have a greater ratio between how much it participates in gravity and how much it resists a change in state of motion.
Einstein said that "gravity and inertia are identical in nature", not just gravitational and inertial mass. Putting the qualifying subscript to distinguish inertial mass from gravitational mass in the equations wrong. It is based on incorrect preconceived notions that should have been cleared up over 100 years ago when Einstein informed us of this.
another awesome video. pls keep making them!
I didn't know that physics is everything, but I 'm beginning to lean in that direction. The fact that inertial mass and gravitational mass are the same, sounds very interesting.
Best physics videos ever!
I don't understand the math, even simple Algebra like this because I was a fool and made no effort in school, but I really appreciate that these videos exist for those wiser than me.
I feel like showing these to kids in middle school would strongly counter the attitude "how's this stuff going to be useful to ME?" Had I known algebra was so useful to understanding incredibly interesting stuff like physics and the universe, I am sure I'd have made an effort instead of doing the bare minimum and immediately forgetting it all.
as an electrical engineer I listen to your videos quite regulary to learn more about physics around and ask myself , why did I study electronics? Tnx for sharing!
I love this channel because I get authentic explaination for the facts that blow our mind.
I like the way this imparts a sort of “thingness” To space instead of space being just a completely empty container defined by spatial dimensions.
Absolutely love this channel. Greetings from Puerto Rico.
This concept was just amazing. Till now I was getting my mind blown by all the concepts I didn't know. But this one blew my mind by something I thought I knew and understood pretty well. It's like finding a secret room in a house that you have lived in for years!
I just didn't understand why inertial and gravitational mass are necessarily equal. I mean, can't they just be proportional?
I don't know a lot about Newton's and other physicist's experience to find the constant G. But couldn't we readjust G to make it work.
For example, let's suppose mG = mI * 2. So mG/mI = 2. So, in order for the expression
F = m1G*m2G/m1Ir²
To still be true, we would just need to adjust G to be half of its current value.
Basically, cant both masses just be proportional?
Newton's law of gravity doesn't contain a m-squared element; it contains an element of "mass of the first object" times "mass of the second object". If we multiply the gravitational mass of each object by 2, and divide the gravitational constant by 4, the force remains the same; and if we do this while keeping the inertial mass the same, the acceleration remains the same. (In other words, we can assume that gravitational mass is not the same as inertial mass, as long as the ratio of the two is constant for all objects, and get a theory which is mathematically equivalent to Newtonian mechanics.)
ScienceNinjaDude Isn't it
F = Gm1m2/r². ?
Where is the m² here? You mean that m1m2 ~ m² or what. Still, what would that affect my reasoning?
Yes, you could assign the constant ratio of M[grav]/M[in] to be anything you like, including units.
This would carry with it, a counterbalancing change in the value and units of G.
So there being no compelling reason for any particular value for such a ratio, the easiest choice is, just make it = 1.
True but the point is that the ratio of the gravitational charge to the inertial mass is a constant for all objects. This is not the case for the ratio of the electric charge to the inertial mass between different objects. For example, an electron has a different electric charge to inertial mass ratio compared to a proton. It's possible to add a certain amount of inertial mass to an object without adding any net electric charge. However, whenever a certain amount of inertial mass is added to an object its gravitational charge always increases in direct proportion. We can choose the value of this ratio to be whatever we wish, so long as we invent a system of units to distinguish between gravitational charge and inertial mass. The value of G will take on different values depending on the value of the gravitational to inertial mass ratio that we have chosen in our new system of units.
We already do something similar when it comes to measuring distances and time intervals. We use one unit to measure distances and another unit to measure time intervals. We could easily use the same unit for both distances and time intervals.
Sir.. what would happen it they (inertial mass[Mi] and gravitational mass[Mg] ) are not equal.. what would happen if Mi > Mg or
When Mi
Inertial mass does NOT resist motion but it does resist changes in motion. Rather basic to the whole question i would have thought.
3:40
So if an object is at rest there is no resistance? Really
This is a great theoretical (via equations) demonstration of the difference between gravitational and inertial mass. I understood the difference before, but now I can point to the two equations which involve them and how they connect. Thanks!
plzz make a video on matter antimatter symmetry
School teachers often use horrible explainations. They’re probably all wrong. These 10 minutes were amazing. Next video should be why some materials are opaque and others aren’t.
Here is a little extra for those who would like to know. The moment of inertia is like mass in the sense that it resists changes in motion. However, the type of motion that the moment of inertia resists is rotational motion.
50 years ago in school I asked my physics teacher why he sets both masses equal. If there is a "m" in the inertial law and a "m" in the gravitational law those "m" must not be the same. Nice to hear about that question today. My question today: is the Higgs field only about the inertial law? The light which is not affected by Higgs is affected by gravity.
Don. You're worth your weight in dog biscuits..
Love these videos
i was going to say hes worth more than that and raise the stakes to cheetos... but then i realized dog biscuits are worth more. So instead im going to double down and boost his worth to seasoned boneless pork chops.
From our perspective things seem to fall to earth . They also seem to accelerate when dropped. Finding a frame of reference that clearly explains this action would give way to understanding what gravity is. Thanks for the vid.
2:25 we need more sarcasm like that...god damn telekinesis!!
Soooo you wanna go to hell?
i love the way he explains things and points out the interesting parts
I didn't understand, what is inertial mass and what is gravitational mass?
Inertial mass happens in a Catholic church and gravitational mass happens in a Lutheran church. Both involve very weighty subjects and require the "God particle." If you pray hard enough during mass then God will reach across the universe and bless you. This is sometimes referred to as "spooky action at a distance." Until the day you die you exist in a "superposition" of grace and damnation. After death, you collapse into a particle which will exist either in heaven or hell. This is called "conservation of souls."
Hope that clarifies matter(s) for you, Burt. i wasn't planning to go on so long, but I developed a lot of momentum.
burt591 Inertial mass is how much an object resists being moved, or how much energy you have to expend to accelerate it a given amount. The more massive the object, the more energy you need to accelerate it. Gravitational mass is the force with which the object attracts other objects, and is attracted by them, through gravity. More massive objects (such as the earth) attract others more strongly than smaller ones (such as the moon).
inertial mass is what causes: F=ma (Newtons 2nd law)
gravitational mass is what causes F = Gm1m2/r²
Experiments show that inertial mass = gravitational mass = mass,
so these two kinds of masses are one and the same.
That's not really surprising, but according to our understanding it doesn't necessarily have to be that way (although it, for whatever reason, is).
Ted L. Okay, but I guess that this leaves the Calvinist in either a vacuum or a black hole, depending upon his predestination, and the fact that Calvinist teachings exclude the notion of mass
Simply put... inertial mass the resistance to change in motion & determines how much energy is needed to change an object's motion.
Gravitational mass... effects how severely space is warped & the density of an object.
That Galileo dropped weights from the leaning tower of Pisa comes from a biography written by a man who had been his secretary for many years (though after he left Pisa). We have a statement from Galileo's own hand that he dropped weights from "a high place" while he lived Pisa.
Wait. What if gravM/inertM = G? What stops us from thinking that? I’m curious!
Andre because G is just a consequence of our measure units. In natural system of units G is exactly 1
it won't work. By symmetry. See the issue from the perspective of the particle and the ratio for the earth will be G too. You get a G^2 term. Repeat for multiple objects and you get a theory that does not work as expected. Finaly it has been messure to a high presition. Also Clocks do slow in grabittional feels, we have messure that with atomic clocks. So it looks correct to a high degree of presition.
The point is that the ratio of the gravitational charge to the inertial mass is a constant for all objects. This is not the case for the ratio of the electric charge to the inertial mass between different objects. For example, an electron has a different electric charge to inertial mass ratio compared to a proton. It's possible to add a certain amount of inertial mass to an object without adding any net electric charge. However, whenever a certain amount of inertial mass is added to an object its gravitational charge always increases in direct proportion.
We can choose the value of this ratio to be whatever we wish, so long as we invent a system of units to distinguish between gravitational charge and inertial mass. The value of G will take on different values depending on the value of the gravitational to inertial mass ratio that we have chosen in our new system of units.
We already do something similar when it comes to measuring distances and time intervals. We use one unit to measure distances and another unit to measure time intervals. We could easily use the same unit for both distances and time intervals.
“We’ve all been indoctrinated in the idea that there is only one kind of mass “
The textbook of my high school physics stated that there are the inertial mass and the gravitational mass, and the equivalence of the two cannot be taken for granted.
Cool video Dr.
So to summarise: Thanks to Einstein starting with a hypothesis, working through relativity, we now know that mass is mass...
Where do I apply for a study grant?
ha ha ha
That was the most words ever used to say absolutely nothing.
Absolutely
@Kungpao Kitty I actually agree with the sentiment. Dr. Lincoln thinks these videos are about him, not physics. I just unsubbed because I can't take his ego and lack of clarity anymore.
@pyropulse gibberish
Lol he really said that many of us wouldn't appreciate the significance of this and here the examples
You have opened many minds. I thank you for your endeavor to enlighten us all.
(1/1)(6.67430*10^-11(5.972*10^24/(6.357*10^6)^2) = 9.8
Hmmm, it works.
Yeah of course it works
If you understood mathematics you'd understand that you didn't even have to test that haha
I do not comprehend this at all. True story: When I was five I understood that things were made of atoms. One day my older brother asked, "Will a 10lb steel ball fall faster than a 5lb steel ball?" (he was always trying to trick/teach something), I took a moment, imagined each atom falling, realized that the heavy thing had more atoms but individually they would behave the same as the atoms in the lighter thing and said "no". At the age of five (still blows his mind). So, I do not lack for intuition about these things but I absolutely do not 'get' the difference between gravitational mass and inertial mass. The speed something falls will be resisted by its inertial mass or it would fall at the speed of light with any arbitrary force accelerating it (small or large). I don't comprehend how a universe could possibly exist (this one or any other one) if gravitational and inertial mass are not the same thing. I do not mean the same value, I mean the same thing. That's how it fits in my head but I'd be thrilled if someone could separate those two things in a way that I 'get it'. This video (and I love these Fermilab videos) did not do that. Didn't even scratch it.
(Another of his test/tricks was this (when I was 9): "If I tied a rope to each end of a spring scale, gave one end to you, and you pull 10lbs and I pull 10lbs, what does the scale show?" [Hint: (that he didn't give) Think of a fence post.]
Beginning: Tells us there is two kinds of mass.
End: Tells us there is only one kind of mass.
lmao
That Einstein guy. He thought of everything!
I really like this channel's videos.
Doesn't inertial mass depend on velocity in relativity?
What would the universe look like if inertial mass and gravitational mass were different?
ScienceNinjaDude it does, though
He said that was the opinion of most physicists, but that there are still some that disagree.
If the change in momentum at relativistic speed is not due to a change in mass, but to the Lorenz factor gamma, that still leaves open the question of what physical interpretation to give gamma, which he didn't address in that video.
1. Ditto ScienceNinjaDude. Plus which, accepting "relativistic mass" would require different masses for the same object, in different equations! The usual rel. mass derived from rel. momentum, doesn't work for, say, rel. kinetic energy, and so on.
2. Well, for one thing, general relativity would be out the window, because it absolutely hinges on that ratio being constant.
Short, concise, and clear. Perfect!
"this isnt about relativity"
talks about equivalence principle and then relativity
lmao
This is a very cool video channel. I originally found them looking for videos on QCD. They do a good job of explaining it and going deep enough to satisfy me but not over my head
nice acdc shirt
he's obviously into heavy metal physics...
It says "Tesla".
Actually Teslas do a DC to AC conversion for the motors.
yeah, because fuck edison!
So in conclusion it's a dcac shirt?