What Is Weightlessness?
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- Опубликовано: 3 окт 2024
- Do you have weight in space? Is weightlessness an absence of gravity, or actually an absence of forces pushing against it? Andy unpicks what weight really is.
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On one hand, we learn at school that weight is the force on an object due to gravity; on the other, there’s a more subtle understanding of weight as something we feel and discuss every day. How these two ideas fit together can cause some confusion, particularly when the idea of weightlessness and astronauts in orbit on the ISS is introduced.
When we tackled weightlessness for the 2016 CHRISTMAS LECTURES and our online series, A Place Called Space in December last year, we spent a long time thinking about weight. This video shares some of those thoughts.
For example, when you’re in freefall, are you weightless? Is weightlessness a consequence of freefall, or is freefall, in fact, a consequence of weightlessness? Andy explains.
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Similarly, in the absence of gravity, accelerating in a spaceship will create the appearance of having weight.
As the video explains, there's no such thing as absence of gravity.
+SebastianMisch
As a more accessible example, the perceived increase in weight when an elevator accelerates upwards, and perceived decrease in weight when it accelerates downwards.
absence of gravity? did you even watch the video?
he means in an ideal sense. take gravity away, and an accelerating reference frame is indistinguishable from a gravitational field.
That means Acceleration and gravity are the same thing
The very last thought was an interesting one. That's an interesting way to think about it.
This video is quite confusing.... can we start from the beginning? Why you have a little chicken on your desk...?
In my school we actually discussed weight and mass almost in the same way. Thanks for the great video!
+Andrey G Same here. It was really confusing when I started to teach myself about physics.
+Andrey G My thoughts exactly.
We where always taught that mass is your inherent "stuff" which is always there regardless of "weight" which is the force you experience due to the gravity of the earth.
This is why we would "weigh" less on, say, the moon, whereas we would still have the same "mass".
These guys seems to be explaining physics without actually having learned it, or at least the terms involved.
Good try though, I guess?
+cortster12 what I meant is that I was taught in the same way as in the video, so not confusing at all
+Metal Monkey or maybe they are trying to explain to people that can't grasp the regular definitions. Better than nothing.
Andrey G
Hmm I may have started reading comments halfway through this vid and not heard something... Another comment forthcoming.
A very clear video that explains the issue with precision-thank you! You only omitted one thing: some people think that 'free fall' implies weightlessness happens only on the way down. The confusion is natural because of the word 'fall', but it needs to be corrected. I remember a huge argument in the 1990's on a roller coaster enthusiast group (yes, on USENET!) about Supeman: The Escape, the first ride to use linear induction launch. It gave the rider six seconds of weightlessness as they were shot up a tower and back down. Some people were insisting that it was three seconds because the 'up' portion didn't count!
Falling ONLY happens on the way to the centre of the Earth. You cannot fall upwards away from gravity. In fact that makes you heavier.
Fab video! I often struggle to communicate this idea to others but you made it very easy to understand.
+Jeremy Mango Thanks!
+Jeremy Mango An even easier way is to think of "weight" as the force exerted on your body due to the earth's gravity, while your "mass" (physics term) is your actual molecules counted up and totaled, which does not change regardless of your position.
You "weigh" less on the moon, because there is less gravity to pull on your "mass" which does not change, unless you eat or exercise more, thereby increasing or decreasing the actual "stuff" you are made of.
In space you can be "weightless" all though the term these days is "micro-gravity" because there is always gravity pulling us somewhere, even if it is too weak for us to perceive.
Though to the human senses, orbit around earth, or a trip outside of the major gravitational fields of nearby bodies (planets, moons, stars etc) would functionally be felt as "weightlessness" to any normal human.
I don't really know if this clears things up, but technically it IS more accurate, from a physics standpoint, as I have been taught.
+Metal Monkey
Except one never can "take a trip outside of the gravitational fields of nearby bodies". This IS one of the major problems people have envisaging the reality. And your inaccurate terminology simply help preserve that misunderstanding.
As he says clearly in this very video, one is still constantly being gravitationally attracted to anything with mass, it just becomes less with greater distance, in accordance with the inverse square law.
As he also says clearly, it isn't that one is in space so gravity isn't now attracting, the object is travelling so fast as to be constantly falling at the speed to counteract the gravitational field. Otherwise one would either slowly spiral into the object (earth), or if going faster one would spiral out.
rationalmartian
And, as I stated earlier, the orbital stuff is absolutely correct.
And it IS possible to travel to a point in space where major gravitational fields counteract each other at least, such as a distance roughly 4/5ths the distance to the moon from earth.
The explanation I gave holds for deep space though, where you would NOT be attracted by a major gravitational field. At least, not enough for our feeble human senses to feel.
And since when is my terminology inaccurate? I believe I have at least given the physics answer to the best of my understanding, if you disagree, please, give examples instead of just shitting everywhere!
Andy Marmery is the best!
I think it's surprising to most people when you tell them if they stood on a tower as high as the ISS you would not float away.
Quote:"Do you have weight in space?" Before watching the video I can say yes. That is why you are always falling, be it on earth the moon or in space, you are always falling.
Concept Checking Question: If you built a skyscraper 400km high (which is where the space station orbits) and you stood on top of the skyscraper how much would you weigh?
Concept Checking Answer: You will weigh ~90% of what you weigh on Earth's surface. Way more than zero, as some mistakenly believe.
Let's take a person with a mass of 80 kg. Assuming local gravitational acceleration is 9.81 m/s^2, their weight is 784.8 N.
400 km above Earth, gravitational acceleration is around 8.68 m/s^2, so the weight is around 694.5 N.
Mass is, of course, the same 80 kg, but on a typical scale, which is basically a dynamometer with a calculated mass scale, it would register as 70.8 kg.
Thankyou for making me understand weightlessness ☺
the misconception of space weightlessness is still unclear to me? so the floating of space is caused by the constant overshooting of the ISS so that no counterforce is there to create "weight"?
Yes, just like in a falling airplane or an elevator (few seconds, before air resistance starts to overcome it), you're not being pushed against anything and you move together with the room you're in.
That's how "Upside down and inside out" music video was made. (ruclips.net/video/LWGJA9i18Co/видео.html)
There are, however, tiny forces arising from various factors that will ruin perfect weightlessness in orbit, so to describe the conditions on ISS we use the term "microgravity". It's a quite unfortunate term because it implies there's "very little gravity" which is really not the case.
For example, different parts of the station are at different heights from Earth's surface which means they're on different orbits. Tighter orbit = more speed, broader orbit = less speed. Even if the difference between two objects is just 1 m, their speeds do not match and they eventually drift away, and end up clinging to the walls of the station.
There are more causes for "microgravity" but this one is the most pronounced one.
Weight = Mass x Acceleration, which is the same as Force. If you're not in contact with an accelerating body, you are weightless. When you're in freefall (orbit) you are weightless.
Gravity itself is not a force, there is no force of attraction. Gravity is an effect causing the Earth to accelerate up underneath us in curved space-time. Einstein's General Relativity.
What a great explanation.. thank you 😊
Well, when I was studying physics years ago the taught us that weight is a force the body is applying on it's support, caused by gravity.
That was a definition of weight as physics understands it. And onboard the ship orbiting the earth, the Vomit Comet in it's "zero g mode" or free falling elevator cabin there is no weight indeed. Which does not mean there are no gravitational forces.
And speaking of misconceptions, center of the Earth is no special point at all. It is not even the exact spot the vector of free fall acceleration is pointing to :)
the definition i learned was weight = mass x 9.8 m/s²
I think pointing out the difference between weight and mass might have been a better way to do this?
Imagine, as you explore space. You use a device to detect a gravitational field and use it as wind to pull your ship towards it. SEA EXPLORATION VIBE
Thank you foe the video!
Weight is defined as the measurement of gravitational force acting on a body, and in the case of freefall, the body is said to have zero weight? Doesn't that mean no gravitational force is acting on the body? And if this is the case, then why is the object pulled down?
I can understand weightlessness in case of satellites orbiting in the orbits, because in the frame of reference of the satellite, the centrifugal force balance the centripetal force provided by the gravitational force, hence the net force becomes zero.
How can it be justified in case of freefall?
look up einsteins general relativity.
gravity is not an actual force like other forces.
its an effect of spacetime that is bent due to mass.
GCSE’S tomorrow
Any revision tips
Yes. Stay safe from corona.
So technically speaking, one can not be static in the deep space right? i mean even if we are in a very isolated place, the attraction of gravity of any massive object, even dark matter, will attract us to them right?
Yeah it has gravitational force has infinite range I believe
That, and there's the problem of determining your speed and velocity. Without reference points, you can't tell. Movement is relative, and when describing it, we always have to mention the reference point.
Lajos Winkler but we can tell if we are accelerating
Thank you for clearing the confusion sir! :)) 😀
easy mode:
imagine standing in your yard and you have a ball.
if you throw the ball sideways it will travel a certain distance before hitting the ground.
now if you throw that ball a little higher and a litter harder, it will travel a longer distance and take a longer time to fall.
now imagine you throw the ball so hard, it goes through the clouds and reaches space, where there is no air, no friction, no obstacles to slow it down. if you threw the ball at just the right speed and angle, the ball will get stuck falling towards earth as theres nothing to stop it. its simply going too fast with no friction to fall to the earth. but it is still falling, and maybe millions of years from the time you threw the ball, it will begin its re entry into the atmosphere and fall back towards the earth. the ISS is falling and will also eventually reach the same fate. (it will take a very long time though)
Weight is a value on earth. There is no weight as a concept outside the gravitational field.
You're not outside the gravitational field in orbit.
why when something is on the orbit it goes sideways around the earth and not straight down?
once the satellite is in outer space, the gravitational force due to earth is perpendicular to displacement/ velocity at every point, nd therefore earth can't naturally pull it once it is in space. Work = F X S cosα nd α = 90 , therefore the earth's gravitation just serves as centripetal force
Your question is wrong. If something is in orbit, it means it's going sideways. It's like asking why is the Sun's surface hot if it's at almost 5800 K. Orbiting means going sideways around Earth (or any other body).
Correct question would be: "Why is orbiting possible, why doesn't something fall down?"
Answer is - because it has enough sideways speed so that it constantly misses the surface (or denser parts of atmosphere).
its going too fast to fall, and theres nothing to slow it down. but it is falling and will eventually re enter earth in a very very very long time.
We can also experience weightlessness when an equal and opposite force is exerted against gravity to neutralize the net force.
It's not a chicken it's a rooster
Note that the term microgravity makes it worse. After all, there is nothing micro about the total force between you and the earth when in orbit. The gravitational field is just as strong and isn't micro in any way.
Well, it's not "just as strong", but it's not way less either. It depends on where you are in orbit, but for a typical low orbit, gravity is about 85-90% of what it is on the surface.
I always hated the terms "zero-g", "micro gravity" and even "weightlessness", since people don't always understand the difference between weight and mass.
I prefer to call it "freefall" as it describes the situation perfectly without confusing any terms to people. Freefall clearly suggests that you have both weight and experience gravity. It's nice to see someone else finally make a bit of use of the neglected term freefall for a change. Now, if we can only make it stick, and get people away from that pesky zero-g thing...
+maclypse But when a skydiver is in freefall they are still experiencing a reaction force in the form of air resistance and that is what confused me. I was confused whether the skydiver feels like there are no external forces or whether the skydiver would feel like something was softly cushioning the fall. Ignoring the air rushing past the ears of course. I think the latter is true which would make even calling it freefall a little confusing.
@@noodlesthe1st skydivers definitely feel a force. the wind friction in the atmosphere is not a soft cushioning. theyre not able to freely move around and skydiving acrobatics are incredibly tricky.
if you are in the confines of a plane cabin and the plane is going down at the same speed you are, it will LOOK like you are floating around, but youre really just falling towards earth, it feels like weightlessness because there is no wind friction. it makes you feel like you are floating.
So if I got into a plane that flew at 30,000 feet, there becomes a speed where I would not experience gravity?
I've wondered about these helium balloons going to the edge space, if you had a set of scientific digital scales with a 1kg mass on them, what would that mass weigh on the scale the moment before the ballon popped?
+Green Silver The scales would show a decrease in the number it shows. Scales actually measure weight, and are calibrated to convert that number to mass by dividing by g (9.8). However, as distance from earth increases, g decreases with an inverse square law, so the apparent mass would decrease.
+Green Silver Yes. A fast plane at 30,000 feet would at some speed be fast enough to not experience gravity. You'll melt from the friction long before that point though.That speed ought to be about 30,000 kph or 20,000 mph. The ISS skirts around just barely outside the atmosphere and orbits at 7.66km/s (27,500 kph)
+Sam Pibworth Specifically, at 30000feet, g=9.77, instead of 9.81. Thus your 1kg mass will appear to weigh 0.996kg. So not much change...
Sam Pibworth your 1kg mass will be 1kg and will be 1kg no matter where it is. It's weight will change.
1:15 is that bad lighting on purpose? Hard shadows, blown out highlights illustrating the viewers lack of accomplishments and failures?
Seriously though, I hear weight and mass being used as an equivalent measure and that's just wack-a-doodle. My mass is the same no matter what planet I'm on, but my weight would change depending on how many movies that planet appeared in. That's why I would weigh 400 pounds on Jupiter but only 11 pounds on Pluto, but here on Earth, I'm a solid and slim 175 pounds. Or kilos. I forget. I'm a giraffe.
Mass is a measurement, weight is a relationship.
+BariumCobaltNitrog3n I think you missed the point of the video being distracted by the lighting. The point was that astronauts on the ISS feel like they are in microgravity yet they have weight almost identical to that on earth. Not that weight changes on different planets.
My question is weightless are only in space?
No. The feeling of weightlessness has nothing to do with space directly; it has to do with the fact that objects in space are generally in a state of free fall. The problem is that true free fall is a state where the only thing having any effect on you is gravity. A sky diver for example is not in free fall because drag counters gravity. You can get pretty close to free fall, and therefore weightlessness, in short falls in air before drag becomes significant. There are many thrill rides that incorporate free fall in their rides so that riders experience brief moments of near free fall - and you feel weightless on these portions of those rides.
Falling
I was thought that "weight" is the force and "mass" is...well mass.
If I weight a person in moon I would get different results because of force of gravity is weaker. | force
If I E=MC^"2 that person the same 'pop' would be emitted. | mass->force (f... time)
weight = mass x 9.8 m/s² (this number is the force of gravity and is constant)
e = mc² is einsteins theory of relativity.
it shows that energy and mass are interchangeable. The theory of special relativity explains how space and time are linked
I don't have weight in space. I never have weight when the mothership picks me up on Saturdays...
No mention of mass?
Mass is a constant. Yes, it should've been mentioned because most people don't understand what's mass and what's weight.
@@lajoswinkler mass is not constant, it changes all the time depending on what object you are measuring.
mass is found by multiplying the density of an object with its volume.
can you prove the earth is a globe? there's a lot of people on RUclips that think it's flat and gravity is a myth, I know it sounds silly but seriously how do you prove beyond reasonable doubt it's a globe and not a flat disc?
+MomoTheBellyDancer but what about b.o.b? He's like Jesus
I think enough 'normal' people have stuck a GoPro onto a balloon and got a nice view of the curvature of the Earth. There are still deniers because there are still retards. Just look at the state of evolution.
+Phillip Parr these 'flat earthers' have an answer for everything, the go pro footage from high altitude that shows a curve is just caused by a fish eye lens. they are convinced everyone is brainwashed into believing the earth is a globe and it's the mother of all conspiracy's that the earth is really flat. they cannot accept scientific facts, they just say they are wrong or space footage from the iss is fake, plus the iss is fake, it's proper crazy shit.
Phillip Parr, now you've gone into another extreme - using disinformation to prove the opposite. That's not good.
Those cameras do not show curvature. They indeed distort the image. They have wide angle lenses. Depending on the position of a straight line in their field of vision, it might even look like a bowl. Does that mean we live in a bowl? Of course not.
Looking through our eyes, curvature barely shows at Kármán line (100 km). When I say curvature, I mean literally horizon bending downwards from the horizontal line and not the optical illusion that arises from one being above most of the atmosphere and all obstacles, which is horizon going around you.
Actual bending is very gentle even at low Earth orbit where International space station orbits. Again, you need to find photos and videos made with normal lenses (still not like human eyes, but close enough) and not wide angle ones used by monitoring and navigational cameras.
Now get four times closer to the Earth (100 km) and you'll see you're just beginning to notice it. Get low into the stratosphere and it's gone.
To _directly witness the curvature_ is one thing, but to _detect_ it and show its effects, you can be on the sea level. Simple ship mast observation when it sails away, or witnessing two sunsets if looking at one's end and jumping up immediatelly afterwards, various shadow lengths at different places at the same time, etc. Lots of neat experiments even ancient people knew about.
When confronting the stupidity of the flatearthers, one must not succumb to myths. They're experts at it and will use it to their advantage.
Speak slowly
wow
Hmm... the absence of obtrusive magma in space combined with speeding means you cannot bump into the Earth and you are oblivious of the bind of gravity vulgo weight... just like Alice falling into the rabbit hole... no magma... except she did not experience free fall, she fell slowly so she must have experienced weight... ah well , enough gravitas.
Good video.
What a ridiculous video. How do you fall up?
Stop calling gravity as a force ffs
There is nothing wrong with treating gravity as a force. It was certainly treated as one when they calculated the trajectories to land on the moon.
@@willoughbykrenzteinburg I'm not going to degnify this with a response lol
@@3Chandresh3 ....as you respond...
My theory is more believable, less than a month i've seen two figures in the clouds, a circle and a triangle in tangent. And now i have in mind how weightlessness work in outer space maybe came from heaven. see volcano watchdog in FB for more theories
Why do you do this? This is a science video channel for people who are interested in science. Why tell the same old tired 17th century story that we were taught in school? We abandoned this view of gravity over 100 years ago. No-one alive now did their science training before we knew better. Gravity isn't a force. Surely surely you can tell the real story on a platform like this? These are people who have taken the time to learn what's really going on. Like I said, it's *100 years*, LIGO has confirmed the last predictions of the theory. When do we stop teaching that it's the beating of angels wings?
+gasdive He never said gravity was a force. He said weight was the force on your body caused by gravitational acceleration and specifically referred to gravity as a field. But go on then. Explain the 'real' story. Hope it's not about gravitons, seeing as noone's yet proved they exist
DeadFish37 "He never said gravity was a force"
1:35
"But go on then. Explain the 'real' story"
GR
+gasdive That can just easily be taken to mean the force caused by gravity. I realised that second bit shortly after typing it, but would it really benefit us to think of it that way? Physics is all about simplified models and they may not have been thinking about it in GR terms themselves because it's virtually irrelevant this far from any large mass
+gasdive At the end of the day whether it's inertia being stopped by a force, or a force being stopped by another force, not being affected by a stopping force is still the result he's discussing
It's called using a model to teach the basics. It's neccessary.
This video is completely wrong. Weightlessness is when you accelerate towards the centre of the Earth at the acceleration of gravity. And the corresponding diminishment of distance between the centre of the Earth and the falling body. You cannot fall around the Earth. that is nonsense.
shut up
Make a guy white and give him a British accent, and he can tell us anything. The earth has no center. He cannot prove it because the earth is supposedly 4000 miles deep. The problem with this is that no drill has ever drilled deeper than 7 miles. So, I suppose, how could he make an assumption that the earth is 4000 miles deep and has a core. But then, he has a British accent and a globe on his desk.
If you could reject the existence of things that you have not seen, the world would be a pretty small place - and very oddly shaped. Your argument here is just that of an uneducated fool.
To answer your other question - falling in physics is simply being only under the influence of gravity. When you throw a rock in the air, if is falling toward the Earth the entire time it is in flight - on the upward bound journey as well. It is accelerating toward the Earth at 9.8 m/s² the entire time. I wouldn't call it falling upward though - it is still falling toward the Earth; just moving upward.