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Re: Friction



On Thu, 29 Oct 1998, Glenn Knapp wrote:

All the physics book tell us that the frictional force is independent of the
area. One year a student listened to yours truly repeating the idea. Student
then asks, "Well, if the area doesn't matter, then how come fat tires on a
race car corner better than skinny tires?"


Wider tires have been mentioned more than once in this thread, with the
assumption being that increasing the tire width results in increased
contact area. I would question this assumption based on an experimental
study my students conducted as a class project a number of years ago.

Everybody collected data on vehicle weight, tire pressure and the total
contact area of the "footprints" of the tires on a concrete surface. All
kinds of vehicles; I remember one kid had his trucker dad park his rig on
18 pieces of carbon paper overnight. The agreement to A=F/P was quite
good. Total Contact Area = Gross Vehicle Weight / Tire Pressure.

I don't remember specifically addressing the tire-width issue, but I'm
sure we must have had tires of significantly different widths in our
study. If I am to believe our research, and vehicle weight and tire
pressure being the same, a wider tire should produce a contact area having
a different *shape* but no difference in *magnitude*. Or am I missing
something important here???

Best wishes,

Larry

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Larry Cartwright
Physics, Physical Science, Internet Teacher
Charlotte High School, 378 State Street, Charlotte MI 48813
<physics@scnc.cps.k12.mi.us> or <science@scnc.cps.k12.mi.us>
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