WHY DO STONE FALLS BACK TO EARTH AFTER THROWING IT UP?

Question

anonymous · Answer

Because when you throw a ball upwards, There are a multitude of forces acting on it Gravity, Friction, Force you applied to throw it upward (if you want to just consider the basics). So there must be a point where one or more of those forces is equal to zero. That point is at the very top. So at the very much, for an infinitesmal moment, the force you applied to the ball, by throwing it, is zero because friction has stopped the acceleration on the way to zero. At this point if gravity was not there, the ball float  (also, if gravity wasn't there you wouldn't have to throw the ball), but since gravity is there an acting in the downward direction, the ball falls back downwards.

matthewrlee · Answer

Stones are team players. They want to fit in. Everything else we throw into the air falls back down. Stones just want to be like everything else.

anonymous · Answer

To clarify a few things that Astronomer2231 said, here is a breakdown of forces acting on the stone at various points:

In your hand: gravity (g) in the downward direction.

At the time when it just leaves your hand: force F applied to throw it (in the upward direction), gravity (g) (in the downward direction).

When it starts moving in the upward direction: frictional force (u) (in the opposite direction of motion), gravity (g) downward. The force F no longer acts on the stone. If it did, the stone would never return to the Earth.

At the top-most point: gravity (g) in the downward direction. Note that its velocity is zero at this point. There is no frictional force acting on it either.

On its downward descent: gravity (g) in the downward direction, frictional force (u) in the opposite direction of motion.

A couple of things to note: Gravitational force always acts on the stone - it never ceases and is always constant in magnitude.

If we had only gravity but not friction, the object would move farther into space and move faster in either direction.

If both gravity and friction did not exist, the stone would go into space a constant velocity without any acceleration.

If gravity did not exist but friction did, the stone would move upwards with constant deceleration (proportional to the magnitude of frictional force) and come to a halt in space (and never return).