How can there be no contact force between two bodies stack one top of another during freefall if they are in contact?ho
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You need to be very careful in presenting a question like that to eliminate all ambiguities.
If you stack two bodies one on top of the other on the ground, then there will be a contact force owing to the weight of the upper body being resisted by the lower one.
If you place the two bodies next to each other in freefall in a vacuum, the lower body will no longer resist the weight of the upper body, as they are both accelerating at the same rate.
There may be other forces acting between the bodies if they are in very close contact, such as electrostatic forces.
You must also be clear about how you bring the two bodies together during freefall, as that might determine whether there are any transient forces between them if the bodies are bumped together in some way.
If the bodies are not in a vacuum, then the lower body will meet air resistance which will cause it to act as a brake on the acceleration of the upper body, thus resulting in a contact force.
So you see, you must clarify the circumstances that apply to your question if you want a definitive answer.
answered May 17, 2021 at 9:56
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$\begingroup$ OKAY SO IF LETS CONSIDER TWO BODIES ONE TOP OF THE ANOTHER IN FREE FALL (NO AIR DRAG). IF THERE NO CONTACT FORCES SO NO FRICTION SO HOW DO THEY REMAIN IN CONTACT. DOES THEIR INTERMOLECULAR DISTANCE CHANGES WHEN THEY ON EARTH AT REST. DO IT INCREASE. WHAT HOLDS THEM TOGETHER $\endgroup$ Commented May 17, 2021 at 12:16
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$\begingroup$ They remain in contact because there is nothing pulling them apart. If two objects are positioned a certain distance from each other and are uniformly accelerated they will remain the same distance apart. That is true even if the distance is zero. $\endgroup$ Commented May 17, 2021 at 12:58
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$\begingroup$ does the intermolecular distance changes when there was a normal reaction force to when they are in free fall (ignore are drag) and there is no contact force $\endgroup$ Commented May 17, 2021 at 14:07
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$\begingroup$ If they were initially stacked on a trapdoor say, which was resisting their weight, before being dropped in freefall, then while on the trapdoor each body would be compressed slightly in a vertical direction. Once the trapdoor is opened, that compression would relax. $\endgroup$ Commented May 17, 2021 at 14:12
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$\begingroup$ why do then people start float upwards during free fall like in a lift freely falling why can they just stand still $\endgroup$ Commented May 17, 2021 at 14:55