Question

In lecture 7,
professor has shown a video of free fall experiment done by nasa.
my question is when all of them are in free fall why are human swimming in midair?
aren't they suppose to be intact to the ground and just feel weightlessness?

Answer 1

because of friction with air

Answer 2

Because they are falling at the same rate the airplane does, and indeed you will not feel any opposing force while on air, and consequently no normal forces, which are responsible for making you feel your real weight. When you are in free fall you dont really feel your weight as when you are standing on a static surface.

Answer 3

What would keep a human intact with the floor? The participants are weightless in the frame of reference provided by the plane. As they approach this situation, the plane taking an approximately parabolic path, the floor is not remaining in the same orientation with respect to the force of gravity. In my approximation, which no doubt omits further factors, to leave them intact with the floor this and two other conditions would be required. The plane would have to get its parabolic path precisely correct, and they would be required to resist the temptation to make even the slightest movement - which would apply a force between them and the floor. I think I would be inclined to jump!

Answer 4

I think the situation arises because of the weightlessness. As no force acting on the experimenters and they act like floating dust particles.

Answer 5

i still don't get it people must be falling into the ground as well as plane with acceleration of g.

Answer 6

Dear shubhajeet -- You have a good question, and previous respondents may not see your point. Think of the space shuttle crew blasting into space. At some moment the rockets stop, and their pencil floats off the table and up into the cabin. Clearly the pencil has accelerated relative to the shuttle body, even though both are supposed to feel the same g-forces. So why doesn't the pencil just stay on the table? It cannot float up without some extra force. What is this force?

Any solid object resting on a surface during gravity gets deformed a little bit by the gravitational force pushing it onto the surface. When the acceleration stops, the object is still deformed. The force of deformation is then acting unopposed to push the object off the surface. It continues to push until the object no longer makes contact. The energy stored in the deformation turns into kinetic energy, giving the object a nonzero velocity.

This effect means that if two objects have equal mass, the softer one that deforms more will contain more deformation energy and will rebound faster.