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d4rkh0rs t1_jdu4o4t wrote

And you can move a sled, not far but if you kick out your legs or suddenly sit up or lay down you should get several inches movement.

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Si_shadeofblue t1_jdudoze wrote

But you need friction for that

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d4rkh0rs t1_jdv50z2 wrote

you need friction to stay on a sled, yes. ???

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Si_shadeofblue t1_jdv8402 wrote

What I meant is that to move the sled by kicking out your legs you need to have friction. So you are essentially pushing of the ground which means that this example is not comparable to an earthquake changing the earth's orbit.

Thats what I thought anyway. Might be wrong.

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d4rkh0rs t1_jdvho9w wrote

I thuoght the orbit thing was covered and was responding to the sled.

But they are comparable in the sense that if the rider or the earth change their shape the center of mass doesn't change but from points of view not on the center of mass things appear to change.

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