Falling Through the Earth
So, what WOULD happen if you could drill a hole through the center of the earth and then jump into it? To make it easy, we must assume no air resistance, no bumping the sides on the way through, a perfectly homogeneous mass distribution for the earth, and a few other idealities. About 42 minutes after jumping in to the hole, you would emerge at the other side of the earth, 7,926 miles away, at the same height above the surface from which you jumped into the hole. Unless you grab onto something to keep you from falling back through to the other side again, you would oscillate back and forth forever in 84 minute round-trips.