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Re: Friction



HI,

Time for my 2 bits!

On tire slipage: The extreme case of slippage is a farm tractor
on lose soil. Ag-engineers claim a 20-40% slippage provides the max
power to pull the tractor and attached equipment. Now note that POWER is
quite different than FORCE! Some of this may be true in drag racing, but
I think the real reason as has been suggested by someone is to keep the
RPM's high at startup, something has to be slipping, either the tires or
the clutch, and slipping the tires work best.

For track racing, the cars oversteer ( that is the back wheels
track outside of the front tires) This is not really slidding, but is
close. While watching some of the practice stuff for the Indy - 500 this
year, I heard that the strong oversteer preserves more speed then turning
the front wheels more, and ture tracking of the back wheels in the tracks
of the front wheels

Thanks
roger haar



*************************************************************

On Mon, 15 Jul 1996, John Mallinckrodt wrote:

On Sun, 14 Jul 1996, David Dockstader wrote:

2. Max acc is always achieved with some slippage of the tires. Therefore,
slipping friction must be greater than static friction. Drag racers do not
spin their tires because they are out of control. They do it because it gives
the max acc. Likewise a race car in a turn is deliberately set up to slide.
Sliding is faster. To stop the slide you have to slow down!

Just because max acceleration is achieved with slipping tires in some
situations does not necessarily mean that the coefficient of kinetic
friction is greater than that of static friction. Don't drag racers
simply live with the neccessity of spinning their tires at low speeds
because their engines won't deliver much power at the low rpm's that
would otherwise be necessary?

In the case of cornering racers I'm not so sure, but I'm willing to frame
a hypothesis: A racer taking a turn at maximum speed with nonslipping
tires is *just* on the verge of sliding. Any application of the brakes,
overapplication of the accelerator, or even *underapplication* of the
accelerator that results in engine braking will cause the car to go into
a slide without warning, kind of like trying to run across ice without
slipping. Might it be the case that it just ends up being better from a
control standpoint to allow the rear to break free and use the spinning
rear tires to help provide a more controllable centripetal force?

Any weekend derby types out there?

John
----------------------------------------------------------------
A. John Mallinckrodt email: mallinckrodt@csupomona.edu
Professor of Physics voice: 909-869-4054
Cal Poly Pomona fax: 909-869-5090
Pomona, CA 91768 office: Building 8, Room 223
web: http://www.sci.csupomona.edu/~mallinckrodt/