# Acceleration in free fall [duplicate]

A body in free fall "feels" no gravitational force (equivalence). Why does it continue to accelerate. Why is your program refusing my question?

• Possible duplicate of Why does a free-falling body experience no force despite accelerating?
– JMac
Apr 18 '19 at 16:23
• @Maxim The OP is specifically talking about feeling gravitational force which no freely falling (small enough) observer can feel. Yes, sure, you can feel the drag, anxiety, excitement, and many other irrelevant things--but that is not the point here. Apr 18 '19 at 21:37
• It can also be seen as conservation of mechanical energy(neglecting the losses). The body at a height has potential which goes on decreasing as it falls so the Kinetic energy must increase ie velocity must increase. Apr 18 '19 at 21:41

A body in freefall "feels" no gravitational force

Sure it does! It does on the space station too. You just don't feel it. "Wait!", you say, "you just said I feel it and don't feel it!" Yes, that's because there's two definitions of "feel".

One is "feels a force", that is, "there is a force". In that case all bodies "feel" gravity, even on the space station.

But then there's the other "feel", which is "a sensation on your body". By that definition you never feel gravity. No, really, think about it...

You're sitting in a chair reading this right? Do you feel your butt on the chair? Maybe your elbows on the arms of the chair? Yes?

But think about what you're actually feeling - you're feeling the chair pushing up on you. Just stop and experience it for a second.

Do you actually feel gravity? No! Not directly anyway (your inner ear gets a little finicky).

Free fall is literally the state when nothing is pushing back. You still don't feel gravity in either case. But in free fall, you don't feel any of those things you would normally ascribe to gravity but aren't actually gravity, because you remove those objects.

So the confusion is the question is mixing two very different definitions of "feel". Objects continue to accelerate because "there is a force", but you do not "experience the sensation" because you never do.

• Forces between the fluid in your inner ear and the walls of the chamber that contains it are no different in principle from the forces between your butt and your chair. They "feel" different only because of how the nerves are arranged (sensing motion of the fluid in your ear, vs. sensing pressure on your skin.) Apr 18 '19 at 18:55
• -1: This answer is misleading. There is a force of gravity on a person in the space-station with respect to the Earth's frame of reference. But there isn't one with respect to the local inertial frame in the vicinity of the space station that the space station itself is. Apr 18 '19 at 21:42

Whether you're standing on Earth or falling towards it, a gravitational force is acting upon you. It's because both you and the Earth have mass. The reason you "feel" gravity when standing is because you're being pushed or squished onto the surface of the Earth. It's a solid thing and it's giving resistance so your body, bones etc are being "compressed". That's what you feel. When you're falling there's nothing except for some small air resistance so all parts of the body are equally accelerating towards the Earth and they're not in any strain in relation to each other. So you feel "relaxed" as if nothing is acting upon you.

When you stand still on the ground / on a chair etc you "feel" something.

That something is the upward force due to the ground / chair on you.
The magnitude of that upward force on you is equal to the magnitude of the gravitational attraction of the Earth on you a force which you do not directly "feel".

If you are in free fall with no air resistance then there is no upward force on you and so you "feel" weightless although there is still the force of gravitational attraction on you due to the Earth which you do not directly "feel".
That force of gravitational attraction on you due to the Earth is the force which gives you a downward acceleration.

The only thing that changes is that you no longer feel the ground. You still experience acceleration, but you are not subject to the normal force opposing your weight. You still have a weight, just that you no longer feel its magnitude acting on you.

Imagine an infinite series of nested spheres (like skins on an onion). There is a radial (gravitational) force on each sphere directed towards a mass point located at the center of the sphere. The magnitude of the mass determines the force on the sphere. (the sphere represents the curvature of space around the mass point. if the mass was distributed along a line instead then the sphere would be replaced by a cylinder with a force gradient between the mass line and the wall of the cylinder. however, due to the principal of least action, the mass is concentrated at a point.) Now as we work our way out from the center of the earth we encounter a certain sphere representing the surface of the earth. This is the limit of the earth's mass density. Continuing outward the spheres are just mathematical. When you are standing on the earth the force you feel is not the force pushing down on the sphere but rather the reaction force pushing up. (for every force there is an equal and opposite reaction force). When you are a mile high and in free fall you are passing through a series of spheres (mathematical) who's surface area is ever decreasing and who's gravitational force is becoming less dispersed and more concentrated. You must accelerate to maintain your momentum.

we feel things trough our five senses. Any thing outside the domain of those senses we never feel, see or hear.

We do not have a sensory system to feel forces in a gravity, magnetic or electrical field, but we do have sense of touch, pressure...on our skin, distributed with uneven intensity, like our fingers are more wired with nerve endings.

So when we are not falling free, there is something stopping us, a floor, an elevator or earth. these are pushing against our feet, and we feel their pressure and relate it to a consequence of gravity.

When we are falling free in a gravity field there is nothing resisting it other than very small air friction, so we don't feel a force field. But its there and pulling us down. Say hold a chain letting it hang down, it will hang straight and true vertical, because you and every up hand link is fighting the gravity keeping the one below from falling. Now let it fall it will twist and dance freely while gravity is pulling it down. Why because the restrain of upward force is gone.

just as an example when we watch free parachute jumpers do things in suspension like holding hands and spiraling into flower patterns as if they are weightless, its not because gravity is not working to pull them down, its because they are free from the responsibility of having to fight the upward reaction of their weight on the floor.They are falling non the less. You can mimic that by just jumping up into a pirouette turn, albeit the period of weightlessness is short.

• Yes, sorry, chain. Apr 18 '19 at 23:47