On Fri, 18 Jul 1997 Michael Lorrey <retroman@tpk.net> Wrote:
>>How can a little kid (or an adult for that matter) sit on a perfectly
>>still playground swing, begin rocking back and forth, and within a
>>minute be wizzing back and forth to a pretty good height, without
>>ever touching the ground or other still grounded object?
>Damien Broderick wrote:
>Michael, Michael! It's connected at the top. (Unlike the spaceship.)
>>That doesn't mean anything.
No, I'm afraid it does mean something.
>>Since the rider on the swing is at a standstill, and has no way to
>>push against anything, how do they develop the significant levels of
>>momentum they do?
The rider does have something to push (or pull in this case) against, the
Earth. The child on the swing goes one direction and the Earth moves in the
opposite direction, very, very slowly but then The Earth has a lot more mass
than the child. The total amount of momentum is exactly the same.
John K Clark johnkc@well.com
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