I started the Motorcycle Counter-Steering thread back during winter break
and I'm having a lot of phun learning from the spirited discussion which
has ensued.
Thanks to Jim McLean for his thoughtful, by the numbers, analysis which I
have not yet had time to digest and respond to. Just a couple of quick
comments before typing my next post:
A toy gyroscope spining about a horizontal axis and supported only on one
side will precess in horizontal plane about a verticle axis because the
torque exerted by the weight is horizontal and always perpendicular to the
angular momentum.
A motorcycle moving forward (Gold Wings can go backwards now, slowly) has a
left pointing angular momentum. Pushing forward on the right handgrip will
create a torque which is initially upward and always perpendicular to L
causing the motorcycle to precess about a horizontal axis parallel to the
road through the contact patches of the two tires (just as the gyro
precesses). This precession would continue as long as the force is applied
to the right handgrip and the bike will continue to precess right into the
pavement. That's why I remove the forward push on the handgrip when the
correct lean is established for the velocity of the bike and the radius of
the curve (and *g* too !! in case I'm up in the mountains or on the moon).
While leaning, the bike will follow a curved path as long as there is
sufficient friction to be the needed centripetal force. I should know, on
Highway 1 in Northern Minnesota, I hit some sand on a 35 mph curve going 55
mph (Hang a STUPID sign on me) and the bike went straight into the ditch on
its side with me tucked tightly into it while the bike spun around and
ended up going backward in the ditch. I was ok but the bike had a bent
front fork and busted up fairing. This was before I took the Motorcycle
Safety Foundation course and before I became a certified instructor for
MSF.
Bicycle vs. Motorcycle: When I counter-steer my Multi-track bicycle and
push on the right handgrip, I notice the wheel turn left and the bike leans
right. Come ride with me on one of three motorcycles (a Yamaha Venture
Touring Bike, or a Harley 1200 Sportster, or a Harley Low Rider, and soon,
a Katana 750) and see whether or not you can notice any movement of the
handbars (right or left) when I counter-steer. Logic says that that there
has to be some turning of the handlebars/front wheel but it is so
negligible as to be virtually unnoticeable.
And yet we will lean and go around curves (no more sand on curves for me
-->skills taught and learned in the MSF course would have prevented the
accident mentioned above).
That's all for now. I've got to grade the tests for two Physics Olympiad
candidates who have just finished. One went to Norway last year as a 13
yr. old and scored 5th highest in the world out of 259 contestents (Brag,
Brag)
Bye, DiRT
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David R. Thiessen FUN + PHYSICS = PHUN
Science Department PHYSICS IS PHUN !!
Deerfield High School
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dthiessn@nslsilus.org (Quote sources long forgotten)
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