• Question: if the earths gravaty is pulling in, should that not mean that the moon will hit the earth some time insted of it flooting away

    Asked by rmolloy67 to Amy, Drew, Julia, Kimberley, Sara on 11 Jun 2011.
    • Photo: Drew Rae

      Drew Rae answered on 9 Jun 2011:

      Hi,
      Good question. You would think that because the earth and moon pull at each other, they would come closer and closer and then hit. The reason they don’t is because they are going around each other as well. One way to think of it is to tie a piece of string to a tennis ball and then start swinging it. The string will go straight, which means that it is pulling on the tennis ball, but that force doesn’t make the tennis ball come close to you, it just stops it flying off into the air.

      The earth and the moon are travelling really fast through space, and gravity is what holds them together as a pair.

    • Photo: Sara Imari Walker

      Sara Imari Walker answered on 10 Jun 2011:

      Hi rmolloy67! I like Drew’s tennis ball example a lot. Another way to use that analogy is to think about when you throw a tennis ball. It travels straight for a short while before arching to the ground. If you could throw the tennis ball really really hard so that it would go all the way around the whole Earth, it could actually enter an orbit much the same as our own moon! (Of course this is if there also weren’t things like buildings and mountains to get in the way) Gravity, like the string in Drew’s example, would keep the ball stuck in orbit around the Earth. On another interesting note, the Moon actually gets closer by to the Earth by a couple of centimeters each year. This is not a concern though – the Moon is soooo far away about 385000 km that it is not a problem! And as Drew described, gravity keeps the orbit stable so we are safe from colliding with the moon!

    • Photo: Amy MacQueen

      Amy MacQueen answered on 10 Jun 2011:

      I think these guys explained it really well…don’t worry about the moon hitting you! 🙂

    • Photo: Julia Griffen

      Julia Griffen answered on 10 Jun 2011:

      Wow – Sara’s answer is super! I’ve learnt something here! I cannot improve on that!

    • Photo: Kimberley Bryon

      Kimberley Bryon answered on 11 Jun 2011:

      I think that the other scientists have given fantastic answers to this question. It is a brilliant question rmolly67, I had never really thought about it before!

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