[mrguido (OP)]

I noticed that in when the question about the stone falling through the center of the Earth was addressed, half of the question seemed to be missed. I understood the question as centering around *two* stones meeting simultaneously. If the hole was all the way through, and stones were dropped from both ends and they met in the middle, what would happen? I think the question is akin to asking about the nature of gravity at the very center of the Earth.
My guess is that if they were smashed to bits then the bits would fall upwards towards the mass of the Earth.
Did anybody else hear the question this way?

[paul.fr]

Welcome Mrguido
which show are you refering to? I have not yet listened to last sundays show, was it that one?

[Batroost]

My guess is that if they were smashed to bits then the bits would fall upwards towards the mass of the Earth.

No - inside a solid ball the net gravitational force is still always towards the centre.

[paul.fr]

am i right in remembering that the "trip" would take 42 minutes and a few seconds?

[mrguido (OP)]

I don't remember the exact time, but 42 minutes sounds about right. I also don't remember the exact show, but I think it was about two weeks ago (I listen on the podcast and don't always get to them right away).
I thought that maybe the Earth's density would be uneven enough (because of different layers or maybe pockets of different materials) to cause gravity to pull one way or the other.
Thanks for the response!

[paul.fr]

I don't remember the exact time, but 42 minutes sounds about right. I also don't remember the exact show, but I think it was about two weeks ago (I listen on the podcast and don't always get to them right away).
I thought that maybe the Earth's density would be uneven enough (because of different layers or maybe pockets of different materials) to cause gravity to pull one way or the other.
Thanks for the response!

try searching or wikipedia for: gravity train, don't know why but i always want to write gravy train.

[paul.fr]

here is the wiki link:

http://en.wikipedia.org/wiki/Gravity_train

[Batroost]

The other thing this Wicki article neglects to mention is the Coriolis force. On many sub-surface trajectories the gravity train would be subject to an apparent sideways force as well; actually just due to moving in a rotating frame of reference.

I remember this featured in one Sci-Fi story as a reason why the tunnel had to be stronger on one side than the other!

[paul.fr]

The other thing this Wicki article neglects to mention is the Coriolis force. On many sub-surface trajectories the gravity train would be subject to an apparent sideways force as well; actually just due to moving in a rotating frame of reference.

I remember this featured in one Sci-Fi story as a reason why the tunnel had to be stronger on one side than the other!

Interesting, i never thought of or heard that before.