Hole through the earth. Falling up?

A few years ago a good friend of mine asked me an interesting question i think some people might find interesting. Although we both know it is impossible it's something to think about.
He asked, "If there was a hole all the way through the Earth (Say we start in Australia and kept digging down) and you jumped in, you'd be falling down until you get halfway, but then would you have to technically "fall up"?
I'm sorry if this isnt clear or no-one is interested, but i always found it interesting to picture jumping down but then when you get halfway either way you'd be falling up.
If this were possible, would the speed of the fall down be enough to allow you to fall up to the other face of the earth or would gravity prevent this?
Or would you simply get "stuck" in the middle?
Any thoughts on this, let me know. I'm interested to hear what you all think would happen.
Thanks for your time.

You would fall up, because you have momentum in that direction and gravity doesn't affect you at the center because the gravity of different parts of the earth cancels itself exactly. After you have fallen up a bit, there will be some slight gravitational pull, but not as much as on the surface of the earth.

Thanks for that. I'll be sure to let my friend know the answer too.

A slight variation on the orginal question, completely impossible of course and I'm not sure how much gravity comes into it.... but if a hole was dug from one side of the earth to the other, say from New Zealand to the UK and some guy jumped into the hole in New Zealand..... would he (in theory) emerge feet first in the UK ?

Here's an interesting tale...

www.ourhollowearth.com/SmokyGod.htm

I was watching a show on planitary gravity, I think it was on the Scinece channel. Anyway the diagrams showed a tunnel through the earth, and they dropped a ball into it. Once the ball "falls" past the center, gravity from the side that they dropped it in begins to tug back on it, so it begins to slow down and head bac towards the origin hole. Basicaly it will wobble back and forth and get stuck in the center.

[edit on 14-9-2004 by Xayden]

Back in the 80's I did Further Maths A Level. One of the questions was exactly this. If you dropped a hammer down a hole right through the earth, how long would it take to reach the other end (ignoring air resistance) & describe its motion. If I remmber, because of the variable acceleration, it performed a strange version of simple harmonic motion.....

I flunked the exam, though

[edit on 14-9-2004 by LordofLard]

[edit on 14-9-2004 by LordofLard]

it would definatly start wobbling and start to float in the middle.

Correct, a damped version of simple harmonic motion. Much like a pendulum.

Air resistance would have a large damping effect, because as you pass the central point of the oscillation (the centre of the earth), you will have hit terminal velocity, and your momentum will be limited to this level.

Make any sense?

i must say that would be too fun! if only there was a theme park ride with this principle.

This probably sounds pretty weird and I'm not a bible basher but for some reason this started making me think of heaven&hell.
If your soul is heavy with sin when you die, it falls to the earths center, from where it cannot escape.
If your soul is free of guilt and full of light it floats away into the heavens, where you're free to roam.
Hmmmmm....

Well, first, the Earth is molten, so you'd only get a few miles untiil you burned in hellish magma

But assuming a solid Earth, I am pretty sure you would only make it to the middle of the Earth. Once you passed the middle, gravity would pull you 'down' to the center of the Earth again, eventually settling and floating.