How come in free fall you feel weightless even though gravity is pulling down on you? (ignore air resistance when answering this question).
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2$\begingroup$ Think! Why do you feel your weight ? $\endgroup$– Anubhav GoelCommented Feb 8, 2016 at 10:20
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$\begingroup$ Try riding the express elevator going up, then down, and compare your experiences. Better yet, take a good set of scales with you and monitor the weight measured for some test mass. This is the cheap version of Einstein's elevator experiment. $\endgroup$– Peter DiehrCommented Feb 8, 2016 at 13:02
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6 Answers
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Because what you feel as weight is actually the force you must exert to your surroundings not to collapse, or start falling anywhere. Weightless is just absence of this force.
In fact, I can not imagine what should one feel in a free fall but weightless.
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You feel weightless while free falling because no normal reaction force is present. While sitting on a chair you feel the normal reaction force that chair exerts on you which is equal to your weight and the force you exert on the chair.
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$\begingroup$ It's not just the chair. Being supported against gravity sets up forces inside your body that you can feel - e.g. gravity is pulling your head down towards your neck, and you have to use muscles to hold it up. When you are free falling gravity affects all parts of your body equally and they don't get squeezed together. $\endgroup$– bdslCommented Feb 8, 2016 at 12:05
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$\begingroup$ @bdsl Yes. I just used the chair as an example. :) $\endgroup$ Commented Feb 8, 2016 at 12:15
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The reason you feel weightless is because there is no force pushing against you, since you are not in contact with anything. Gravity is pulling equally on all the particles in your body. This creates a sensation where no forces are acting on you and you feel weightless. It would be the same sensation as if you were floating in space.
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Because you never feel your own weight! I'm sitting on this chair to write this, and I can feel the push of the chair up against my body. That is what I think of as my weight - but it is not - it is the push of the chair against my body in response to my weight! If the chair disappeared I'd be in free fall, and I still wouldn't be able to feel my weight, and I wouldn't be able to feel the push of the chair either - I wouldn't feel any forces at all. This is what people really mean when they say they feel weightless - they mean that they feel no forces on them. (Your weight of course, even though you can't feel it, is there all the time, whether you're falling or not.)
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$\begingroup$ do you mean weightlessness means no normal forces? otherwise your argument is wrong as even sitting on a chair i feel no net external vertical force... $\endgroup$ Commented Feb 8, 2016 at 11:10
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$\begingroup$ @BruceLee sit on a hard chair for a few hours and I guarantee you'll feel something. $\endgroup$– AsherCommented Feb 8, 2016 at 12:42
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$\begingroup$ @Asher no one is disputing that...i am pointing out an apparent misunderstanding in the answer.. $\endgroup$ Commented Feb 8, 2016 at 12:44
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$\begingroup$ @BruceLee I don't think Nick meant to say that it is impossible to feel any force while in free fall. Rather, he is pointing out the difference between the feeling of weight (which we only experience due to a reactive normal force) and of weightlessness (i.e. the absence of the usual normal force). If you and the chair are both in free fall you can still touch (apply force to) it, but it's not supporting you so you still "feel weightless." $\endgroup$– AsherCommented Feb 8, 2016 at 12:52
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$\begingroup$ I'm making a slightly subtle point: your body has no gravity sensors! - we can't directly detect weight, only external forces acting on our pressure sensing nerves. A set of weighing scales, for example, doesn't measure weight, it senses the third-law pair of the reaction force of the pan on the object. If you drop a weighing scale with an object in its pan, it records nothing - proof again that it does not measure weight, but reaction force. A falling person feels no reaction force - so 'feels' weightless - but we never feel our weight. I hope that is clearer. Kind regards $\endgroup$– NickCommented Feb 9, 2016 at 12:22
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You don't feel gravity pulling on you, because gravity doesn't actually pull on you or anything else. Gravity bends spacetime. What this means is that your own perceived frame of reference (a system of coordinates to measure space and time), which is all nice and straight, does not match up with the actual shape of spacetime. So even though you think you are accelerating, you're really not. You're just following a straight path in spacetime at a constant speed. When you translate this motion into your own straight frame of reference, it appears as if you are moving along a curved path and/or as if you are changing speed. This is why there is a mismatch between the sensation of freefalling and the apparant motion of our body while doing it.
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you never feel your weight (you feel weightless ) due to no force reminding your brain of your weight. In case while you stand on earth the earth's crust reminds you of your weight by providing a normal reaction force.
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$\begingroup$ I can tell that you have learnt about forces from school education. I would recommend that you ask questions (so long as they aren't duplicates) because some of the things that are asked straight from school education are about things that other people would be afraid to / not think about asking. $\endgroup$ Commented Feb 8, 2016 at 18:29