Re: Rolling, Static, and Kinetic Friction

[Lowell Herr <herr@catseq.catlin.edu>]

> Don't most people use "rolling friction" to describe the difficulty caused
> by a compressible tire -- the fact that the horizontal tangent to the tire
> is not along the roadway -- such that the tire is always "climbing out of a
> hole" ???

This was not the situation with our toy car as the wheels were solid and 
do not flex.

> > So going downhill, kinetic friction is uphill and static friction is
> > downhill.
>
> In the quoted post "kinetic friction" has been defined as the rotational
> friction on the axal by the bearing surface.  How could it's direction be
> "uphill"?

I have the same question.
> If the toy car is accelerating downhill under gravity and with rigid
> rotating tires, there is no "static friction" -- unless of course the toy
> car has a miniature supercharged engine in it.  

The car was accelerating under the normal and gravitational forces.  
There was no engine involved.

Lowell