What would happen if I drilled a tunnel through the center of the Earth and jumped into it?
Although it would be impossible to do this on earth, you actually could do this on the moon. The moon has a cold core and it also doesn’t have any oceans or groundwater to mess things up. In addition, the moon has no atmosphere, so the tunnel would have a nice vacuum in it that eliminates aerodynamic drag. So, imagine that the tunnel through the moon is 20 feet (7 meters) in diameter. Down one side is a ladder. If you were to climb down the ladder, what you would find is that your weight decreases. Gravity is caused by objects attracting one another with their mass (see Question 232). As you descend into the tunnel, more and more of the moon’s mass is above you, so it attracts you upward. Once you climbed down to the center of the moon you would be weightless. The mass of the moon is all around you and attracting you equally, so it all cancels out and you would feel weightless. If you were to actually leap into the tunnel and allow yourself to fall, you wo
