Re: [Phys-l] (no subject)

["John Clement" <clement@hal-pc.org>]

> Friction is WAY more complicated than first year physics would have
> us believe.
> The rule of thumb equation says that the friction force depends on
> the normal force times the 'coefriction of fiction' or some such
> term. ;-)
> This would imply that if the weight of the object is the same - the
> area of contact doesn't matter.
> Small area => large pressure but same force as a large area.
>
> People who race for glory or for a living know well that first year
> physics doesn't work here.
> They generally don't have much use for folks who QUOTE physics
> formulas either.
>
> A better phenomenological view of friction is that it depends on how
> many 'atoms' of tire-onium can be mashed against the 'atoms' of
> street-onium.
> It's these atoms grabbing hold of each other that lets the car push
> itself forward.

 
While the conventional equation for friction is only a first order empirical
formula, how much deviation is there for racing tires?  Actually some racers
do have a scientific background, and use it in their designs.  The answer
that was given does not give much in the way of clues.  As the pressure goes
down one would expect that the number of atoms in intimate contact/area also
goes down, which makes the classical formula make sense.

John M. Clement
Houston, TX