Re: Some More Problems

[herbgottlieb@juno.com (Herbert H. Gottlieb)]

 Leigh Palmer <palmer@sfu.ca> writes:
> Those are good problems, Herb.
>
> A few years ago at an AAPT meeting held at the University of
> British Columbia I perfomed the demonstration of pulling backwards
> on the lower pedal of a bicycle. I used a very low gear (24") and
> extended the crank. The direction of motion (acceleration) of the
> bicycle depends upon where one pulls along the crank. One can pull
> backwards and have the bicycle move forward!
You don't really need to use a bicycle (or even a tricycle) to
demonstrate
these motions. Just wind a string counter-clockwise around a pulley
wheel.
Stand the wheel on a level surface with the free end of the string
protruding from the bottom of the wheel.   If you pull on the string,
vertically upwards, the wheel will roll backwards.  If you change the 
angle between the free end of the string and the surface, you can make
the wheel rotate or slide forwards.

Herb Gottlieb from New York City
(Where pulling from different angles make a difference)

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