• Question: How come spaceships can be in Earth's orbit, without being pulled by gravity?

    Asked by igloo23 to Leila, Catherine, Adam on 22 Mar 2012.
    • Photo: Leila Battison

      Leila Battison answered on 22 Mar 2012:

      In a way, satellites and spaceships *are* being pulled by gravity. It’s just they are falling towards the earth at the same time as the earth is curving away from it. You put spaceships and things up there with some forwards motion, like throwing a ball really hard, and they travel forwards fast enough (and without the air resistance that you get in the atmosphere) to keep going in a curve, and not be pulled down.

    • Photo: Adam Stevens

      Adam Stevens answered on 22 Mar 2012:

      Common misconception: there’s no gravity in space.

      There is gravity in space! Just as much as there is on the ground (well, it gets a bit weaker). The strength of gravity in orbit is only fractionally weaker than on the ground (about 1/10th less).

      The reason that you don’t feel it is that anything in orbit is in freefall, same as skydiving (where you don’t feel gravity, only the air rushing past you) or on parabolic flights where they simulate zero-g (though we shouldn’t call it that!)

      One of the first people to realise this was Isaac Newton, he did a thought experiment about having a REALLY big cannon that could fire a cannonball far enough that it fell over the horizon. Eventually it would go into orbit

      http://www.physicsclassroom.com/class/circles/u6l4b.cfm

      In fact, if you fired it straight up, no matter how far, it would still come back down again. For something to get into orbit it has to go UP but then also across at enough speed to make sure it comes back down missing the earth, which puts it in orbit.

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