Since Rex is answering scientific questions now, I have one that has been bugging me for a long time. Here goes. If there were a hole in the ground that went straight through the core of the earth and out the other side, and someone fell through it, what would happen? This question was posed to Marilyn Vos Savant in her weekly column in the paper. For anyone unfamiliar with her, she supposedly is the smartest person in the world and is in the Guinness book. She has a weekly column where people ask her questions.
Anyway, I think her answer was that if you fell down that bottomless hole, you would pass through the core and almost out the other side but as you approached the surface on the other side of the earth you would fall again past the core back to the other side back and forth forever.
I don't think that makes sense. I would think that as you fall as soon as you hit the very center of the earth you would stop dead because after all, isn't gravity strongest at the center of earth? Gravity always pulls you towards it, not away from it, so if you fell past the center and towards the other side, you would be going against gravity, right? Well, of course you would burn up as you got towards the core of the earth, but assume that this doesn't happen.
Anyone have an opinion on this?
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McSpotlight: Actually, you wouldn't. Consider the situation as being like a spring held vertically; the Earth's centre of gravity would be the point at which the spring would come to rest (the node or point of no displacement). If you held the spring a distance above the node (i.e. like standing on the surface) and then let it go (jumped into the hole); the spring will fall towards the node, go past it until the elastic tension outweighs gravity, then bounce up again to the node; it will bounce up and down a few times before coming to rest at the node. This is what would happen with the hole in the Earth, assuming that the Earth was perfectly uniform internally and that the person was not signifcantly magnetic.
Can't imagine why they bugged the "smartest person in the world" (if such a thing exists!) with it; a 17-year-old physics student shouldn't have to think too hard about that one.
(In case you're wondering, there is no actual difference between force due to a spring and gravity; it's merely that you can see the cause with the spring, where you can't with gravity. If it still gives you problems, try imagining yourself as linked to the Earth's centre of gravity by a big spring; the only thing that stops you getting pulled towards the centre of the planet is all the stuff in between you and it...)
