Quote Originally Posted by OngBonga View Post
Thing is though, we're to assume that the laws of physics apply, it's just we're making some seriously absurd assumptions regarding isolated systems and the ideal conditions.

If the laws of physics apply, then the ball falls because of gravity, and gravity happens because of mass. We must assume, for the laws of physics to not be violated, that the ball has a non-zero finite mass and so does the ground, and that the ball falls because of gravity, in a predictable way. This is why the ball falls. If the ground has infinite mass, well this seriously complicates gravity and probably a fuck ton of other physics concepts, such that the idea of a ball bouncing off such a surface is ludicrous. The energy released when the ball (this is a pretty loose term in such a gravity field because it's not going to be a sphere) hits the ground will probably destroy the universe, certainly in a ball ground and observer universe.
These are valid points.

If the ground's gravitational mass is infinite, the ball's energy upon contact is infinite, and it will have long since dissociated from being anything you could reasonably call a "ball." Unless you mean a spaghettified ball of plasma, I guess.

All we're really assuming is that the ground's *inertial* mass is infinite.
IRL, there's no fundamental reason the inertial mass, the exertional gravitational mass, and the responsive gravitational mass must all be the same thing. At least, there's nothing yet in the human model which predicts these 3 masses should be the same.
They just happen to be the same, as far as humans can measure.


All we really need to assume is some constant acceleration and a reasonably rigid bouncing surface which is perpendicular to the acceleration.