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Old 2002-10-12, 10:28 PM   #34
Klaas Bil
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Re: How do you turn corners?

On Sat, 12 Oct 2002 12:03:12 -0500, gauss
<gauss.cf7bb@timelimit.unicyclist.com> wrote:

> try the experiment again, but this time, spin the wheel and begin
>turning your self around in place while the tire is spinning. You will
>see once again the the uni tries to twist to turn into the circle.

I tried it and it works the way you described (though the previous
experiment seemed more to the point). The uni twists and since I keep
the seat at a constant height, the uni lifts itself up. The wheel
looses angular velocity in the process (I guess mostly by converting
angular momentum to potential energy i.e. the lift) so I could only do
the experiment in a transient fashion. If the wheel was driven I could
check if the uni stays in the "lifted" state as long as I turn it.

Your formulae and my gut feeling agree that the twist tendency is
proportional to the wheel mass. So if I have a lighter wheel the whole
"turning through leaning" works different, i.e. less. And with a
weightless wheel it wouldn't work at all unless I miss something. That
is still counterintuive to me.

I'll ask my colleague engineers what physical explanation they offer
as to why a coin that you throw to roll in a straight line on a
horizontal plane, but which (coin) is tilted as opposed to being
vertical, starts to describe a circle as opposed to continuing in a
straight line while falling at the same time. And if this is due to
the procession, then try imagine a weightless coin with an additional
point mass at its centre. There the procession explanation wouldn't
work, would it? And still it would ride a circle, wouldn't it? (I'm
not sure, maybe my intuition fails in this hypothetical thing.)
I think that my failure to understand this coin behaviour is core to
my problem.

>You can sustain a conversation indefinately using only four words:
>Yes, no, dude, guess.

Or these: lean, force, moment, circle. :-)

Klaas Bil

I posted only a single copy of this message.
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