swinging a swing
Oct. 28th, 2006 05:35 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
miriam_eA child sitting on a swing, legs too short to reach the ground is, to all intents and purposes, a closed system. Every action has an equal and opposite reaction. Forces in equal forces out. But if that's so, how does that kid manage to get the swing going?
On the surface of it, it doesn't look like it should be possible. Whether you lean back or forward your mass is still simply at the end of the pendulum that is the swing.
Yet we all intuitively know how to do it. You lean back then forward at the right times. At first the movements are tiny, but gradually you add to it, using the resonant frequency of the swing, and you can end up taking the swing to the absolute peak of its travel.
So how the hell do we do it?
On the surface of it, it doesn't look like it should be possible. Whether you lean back or forward your mass is still simply at the end of the pendulum that is the swing.
Yet we all intuitively know how to do it. You lean back then forward at the right times. At first the movements are tiny, but gradually you add to it, using the resonant frequency of the swing, and you can end up taking the swing to the absolute peak of its travel.
So how the hell do we do it?
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no subject
Date: 2006-10-30 08:41 am (UTC)They shift their centre of gravity to maximise movement in the forward direction and shift it to the opposite side to maximise movement when going in the backwards direction. There's probably a bit of momentum to the kid's movements too.
However, the premise to the question is false as the system's not closed. There's a child in it with glucose energy in their bloodstream which is burned to add kinetic energy. (It could only really be a closed system if the child were asleep or dead.)