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 Originally Posted by OngBonga
Questions -
Is the ground perfectly elastic?
Is the ball rotating? Is the ground rotating?
What are the mass ratios between ball, ground and observer? Are there any other masses in this universe?
Are all objects in this universe in thermal equilibrium?
The "normal" assumption in this case is that the ground's mass is much much greater than the ball's mass, and that it is perfectly rigid.
Neither is really true, but when they invoked gravity (well, not necessarily gravity, but some acceleration) in their question, w/o further information, we the solver are free to insert the simplest interpretation of what they meant.
Since no rotation was stipulated, again, we are free to assume whatever is simplest to solve/answer the question. Non-rotating bodies simplify things, so we'll assume that.
The masses are a red herring, all that matters is the local g field is "uniform," so again, we'll assume a "very large" planet that is "very massive." Effectively, we treat the ground as having infinite mass and infinite rigidity. This is simplest. It cannot be accelerated or deformed.
We are free to assume that the floor and the ball are in thermal equilibrium, as that is simplest. I don't think the rest of the universe matters, except insofar that we will, of course, assume that the floor/ball system is isolated from external interactions like heat transfer into either object from the outside universe.
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