The other side of the globe

Just a hypothetical of course but if we stood up wherever we live and were able to fall head up and feet down through the earth and arrive on the globe directly opposite of where we stood, would we arrive upside down? compared to all those standing on the opposite side of the earth?

Nope… you’ld arrive right side up in China.

Actually, you’d gradually slow down as you approched the centre of the earth, where you would stop altogether.

Actually, you’d speed up as you approached the center of the earth. You’d start slowing down after you passed through, till you got to the other side, then it’d start all over again.

Eventually, friction would cause you to stop at the center.

squints But isn’t [simplification] gravity caused by mass [/simplification]? So as you approached the centre of the earth, you’d get closer and closer to being in a situation where you had equal mass on all sides of you, and therefore equal pull from all directions. Yes? Or am I just confused again (a distinct possibility)?

yes, but you have inertia, no? so you’d fall through the center, slow down, and fall back towards the center, until you finally stopped.


Uh-Oh! The truck have started to move!

But but but…(god I’m stubborn)…wouldn’t your inertia decrease as well? Let me just clarify that we’re all thinking of the same hypothetical situation here:

There’s a hole through a perfectly spherical earth, starting at some point on the surface, going straight through the centre, and coming out at a point exactly opposite the entry hole. Gravity on the surface is still the usual 9m/sec^2 (or whatever it is). Yes?

Ok. A person jumps into this hole. At the time of jumpipng in, 100% of the earth’s mass is beneath them, therefore 100% of gravity’s pull is beneath you, and you’re falling at 9m/sec^2. NOW, let’s say they’ve fallen halfway to the middle of the hole, or 1/4 of the way through the whole earth. They’d now have only 75% of the earth’s mass below/around them, and 25% would be above/around them. So they’d be falling much slower (half as fast? I’m not sure, sounds like there might be complicated math-type stuff involved). Wouldn’t they continue to slow down as the amount of mass around them equalised? And wouldn’t they stop when there was an equal amount of mass all around them?
I guess the inertia bit is the part I don’t really understand. Isn’t that dependant on acceleration? And doesn’t their rate of acceleration decrease as they progress down the hole, as outlined above?

Bah. I’m afraid I’m just going to have to test this one for myself…best start digging now, then.

Without working through all the numbers, the idea is that, as long as the “majority” of mass is “below” you, you will still accelerate–as you fall through the earth, that acceleration rate WILL decrease, but it’s still acceleration–in other words, you will still speed up, until you pass through the center of the earth. It will take just as long on the other side for the deceleration to slow you down to a stop (ignoring friction).

Well, Cabbage, I’ve been alternately staring at your post and thinking about it for the last 10 minutes, and I THINK I’ve ALMOST got my brain around it. It just seems so counter-intuitive, that’s all. But it also sounds right, the more I think about it. Gravity I can handle, but inertia just confuses the hell out of me.

The “What would happen to you at the center of the earth?” has been knocked around a few times on this board, already, if anyone is interested. (I’m not going to fight with the search engine to find them.)

The actual OP seemed to be in regards to orientation, however. If one travelled feet-first through the earth, one would emerge from the trip standing on one’s head.

However, the China comment, while popular, is incorrect. You would most likely (beginning in North America) end up in the Indian Ocean and drown.

To figure out what is opposite you on the earth, find your latitude and longitude. (E.g., really rough estimates–I’m not looking them up–would be 35°N 120°W for LA, 45°N 125°W for Seattle, 25°N 80°W for Miami, and 45°N 70°W for Boston. The long border between the U.S. and Canada is at 49°N.)

Change the Latitude from N to S, then use the complement of 180 for the Longitude, changing W for E. (So for Miami, the complement of 80 is 100; the opposite point on the globe is at 25°S 100°E.)

If you get out your globes you will discover that substantial portions of the U.S. and Canada are opposite the Indian Ocean.



I’m all excited - dredged that one up from memories of 11th grade English.

If you want to actually take the trip, these pathetic addlepates can give you more info.

“Some people are worried about the difference between right and wrong. I’m worried about the difference between wrong and fun.”
~P.J. O’Rourke~