Re: Swing and momentum

Scripsit briggs@xxxxxxxxxxxxxxxxx
Henning Makholm <henning@xxxxxxxxxxx> writes:

Friction in the bearing allows it to transmit a small torque to the
turntable. The child starts turning her torso with a torque that it
small enough to be countered by the turntable, then suddenly reverses
her rotation with a large torque in the opposite direction. The large
torque overcomes the friction and the turntable begins to rotate.

I don't think that the trick will work a second time once the
turntable does rotate. It depends on non-linearity of the friction.

If you do the experiment on a swivel chair rather than a playground
turntable, the possibility of multiple acceleration cycles is rather
distinct. I've done that experiment many times.

I didn't succeed with the two different swivel chairs available in my
office. One had so good bearings that I could not even make it work a
single time; the other has so much friction that although I can
acquire an angular momentum for a short time, I am stopped by the
friction before I get a chance to try another "acceleration cycle".

--
Henning Makholm "Al lykken er i ét ord: Overvægtig!"
.

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