• Question: If you dug a hole through the center of the earth,and jumped in, would you stay at the center because of gravity?

    Asked by followtheyellowbrickroad to Meeks, Pete, Stephen, Steve, Tom on 18 Jun 2010 in Categories: .
    • Photo: Tom Hartley

      Tom Hartley answered on 17 Jun 2010:

      This could be completely wrong, but I like guessing these ones. Please forgive me if I am wrong (I quite often get this sort of thing wrong).

      I think you would oscillate between the two ends of the hole, and you would probably wind up lying on the side of the tube near the centre of the earth. If you had a wide hole, you might be able to jump straight down the middle, and never touch the side. Then you would keep oscillating for ever, although air resistance would slow you down, until (I think) you came to an almost complete stop at the centre. If you hit the side this would slow you down a lot (and hurt) and you would stop somewhat quicker. If I am right and you stopped near the middle (the physicists will tell you if I am wrong, because I may have missed something), then being in the hole itself would be an unstable place to be, because most of the mass of the earth would be to either side. So I think (unless you were perfectly in the middle) you would end up falling toward one or other wall of the tube.

    • Photo: Stephen Curry

      Stephen Curry answered on 17 Jun 2010:

      Fabulous question!

      If there was no friction or air resistance, I think your momentum would carry you past the centre, after which point you would start to slow down (because the attraction is towards the centre) but conservation of energy means that you would have just enough to get to the surface at the other side of the world.

      If there was air-resistance, you would still go past the centre but would be dragged back. You’d oscillate about the middle for a while before coming to rest there.

      Of course, all of the above ignores the fact that the centre of the earth is extremely hot and molten. You’d be dead within a few minutes of dropping into the hole.

      Please don’t try this at home!

    • Photo: Marieke Navin

      Marieke Navin answered on 17 Jun 2010:

      i think you would keep oscillating up and down, eventually settling in the middle, subject to oscillations caused by earth’s rotation

    • Photo: Pete Edwards

      Pete Edwards answered on 18 Jun 2010:

      You would fall towards the centre of the earth due to gravitational attraction but as you fell the force pulling you down would get smaller. When you get to the centre of the earth the force on you is zero but you would overshoot and continue to move away from the centre. Now the force due to gravity starts to attract you back towards the centre of the earth and gets bigger as you get further away from the centre. So you would start to slow down and would stop again when you get to the opposite side of the earth.
      So, assuming there’s no air in the hole and therefore no air resistance to slow you down, you would just oscillate between the two ends of the hole forever. You’d behave just like a weight on the end of a spring – bouncing up and down.
      You would only stay at the centre of the earth if you could be placed there.

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