Have you considered the idea that objects randomly start accelerating for no reason, with no forces acting on them?
no because that's literally impossible.
Did it have metal on the inside? Or was it a medicine ball?
no, it was solid rubber all the way through. the chair did have a little bit of a slant, but when we set the ball on the chair, we sat there for 5 minutes staring at it to make sure it wouldn't roll off the chair because of the chair's slanted seat. additionally, in the footage, you see the ball sitting completely still, then, as if hit by something, it falls off the edge of the seat out of nowhere. literally, one second it's sitting 100% still, next second it's on the floor.