system
Given the following post, respond as if you're commenting on Reddit:
human
How would gravity behave in a tunnel running through the center of the Earth?

My friend and I can't reach a conclusive answer on this one :
Consider a perfect tunnel (say, a few meters wide) that runs exactly through Earth's center and through to the other side (I'm ignoring any temperature/pressure logistics for the sake of the question) -
What would happen if I were to drop an object down the tunnel?  Would it get stuck somewhere near the middle, or keep a certain pendulum motion around the center of gravity?
Thanks!
gpt
First, assume it's a vacuum. If it were, then it would oscillate back and forth, and would come back to precisely where you released it every time.

If the tunnel wasn't a vacuum (as it "realistically" wouldn't be), then the object would still oscillate, but come less far back every time, due to wind resistance taking some of the energy. So eventually it would loose all of its energy and stay stuck precisely in the middle.

This is also all assuming the Earth is a perfect sphere, which it isn't. But as long as the tunnel was cut so that there was the same amount of earth on one side of the tunnel as the other, then this will still work out.

Edit: Also, if you've had some introductory physics, it's also a fantastic exercise to work out exactly WHY the object would oscillate back and forth.

Edit 2: As LionsFan correctly pointed out, you wouldn't be "stuck" in the middle, but rather it'd feel like you're floating in the direct middle, as if you were in outer space.