Why do objects bounce when they fall on the floor? Does the floor push back up when an object hits it?
The answer is yes, the floor pushes up on the object and that causes the object to bounce. The floor and the object can’t occupy the same space at the same time, so they push each other away when they collide. The object pushes down on the floor and the floor pushes up on the object. Now, the object’s downward force on the floor affects the floor and may cause the floor to vibrate and has lingering influences on the rest of the room. But the floor’s push on the object affect the object and reverses its motion so that from going downward prior to the impact, the object ends up going upward after the impact.
For example, this baseball bounces on the table. When it hits the table, the ball and the table push on each other. Again, they can’t occupy the same space at the same time. So the ball pushes down on the table and that affects the table and the rest of the room. But the table pushes up on the ball and that upward push on the ball causes the ball to accelerate upward. It goes from heading downward, its velocity was downward and maybe even pretty fast, and that upward acceleration changes the velocity such that the ball ends up with an upward velocity, not all that big because baseballs don’t bounce very well. But that result comes from the upward push of the table on the ball.
So, objects bounce because, when they hit each other, they can’t occupy the same space; they push each other apart. Those two outward forces, one on each object, one on the object hitting the floor, for example, and one on the floor, they push each other apart and that causes the bouncing effects.