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Re: [Phys-l] Another tire question



At 07:52 PM 11/7/2007, Mike E., you wrote:
...

Let me give a counter-counter-example that I think you could probably
actually do quite easily, although it won't be real cheap. Take some wire
cutters, go to your bicycle, and cut out all the spokes from the top half of
the wheels. Get on the bicycle and see if the lower spokes will support
your weight.

Michael D. Edmiston, Ph.D.


The lower spokes alone of a bike's wheel will surely not support
my weight. And yes, a wire-spoked wheel can be considered
at a naive level to be suspended from the upper spokes.

Moreover, the nipples with which spokes are fixed to the rim
are not capable of handling radially outwards directed force.

But the strange thing is, both upper and lower spokes take a share
in supporting my weight. How can that possibly be?

Opposing spokes are in tension. When an upper spoke sees
greater tension, a lower spoke is also seeing reduced tension.

Like tire walls, but much less obviously, wire spokes are elastic.

Would it be too much to expect that a teacher could glue
a strain gage to a wheel adjacent to the rim, across a diameter,
then load the wheel and measure the stress on the upper and lower
sides of the wheel? A car wheel?



Brian Whatcott Altus OK Eureka!