Answer to Question #64212 in Mechanics | Relativity for hamid

Question

if we make a hole across the earth, and then we drop a ball into it, what will be the behaviour of the ball in the hole. specially at the centre

Answer 1

Initially ball would fall towards the center due to gravitational pull of the earth and its speed would keep increasing. However, its acceleration would decrease i.e. its rate of speed gain would decrease. This happens until it reaches the center. At this point its acceleration is zero as no force is acting on it (for it is already at the center).
Once it overshoots the center, ball is still attracted towards the center however now it is going in the opposite direction of the pull. So it starts losing its speed and the rate of speed lose keeps increasing away from the center. This happens till the ball stops (which would happen at a distance from the center exactly equal to the distance from which it was released on the other side).
Once the ball has stopped, it repeats the whole process again and again - it is trapped in an infinite oscillatory motion. This motion is a special oscillatory motion formally called as Simple Harmonic Motion.