Nilay Bhatt asked:
If we form a tunnel between two poles of the Earth and there is a free fall of a marble form the tunnel what will happen?
Ben:: What the theory suggests is that if you were to drop a marble or jump down this hole, you would accelerate as you get towards the centre of the Earth, and then when you pass the centre of the Earth, you'd start to decelerate [accellerate in the opposite direction - for physics pedants]. But because of the energy you'd built up, you would in fact go all the way through to the other side.
Now, if you're lucky and had something to grab hold off then you could get out on the other side, but if not, then the same thing would happen again. You would turn back and you'd oscillate one way then the other and just bounce around between sides of the Earth.
The theory is it should take around the same amount of time that it takes to orbit the Earth, so somewhere around 45 minutes from one side to the other.
You might notice from our previous answers that this assumes the tunnel to be evacuated of air - as the air pressure at the core would be incredible, and you would experience very high drag - a marble would be fine, but could you hold your breath for 45 mins?