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Re: Rolling, Static, and Kinetic Friction



Lowell, you seem to be setting up a convoluted combination of real and ideal
conditions:

I will continue to use the phrase "rolling friction" as the impediment to
rolling due to a flexible tire -- ie the continuous climbing out of a hole
phenomenon:

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

This is an idealism -- *all* real tires flex -- even the little hard plastic
ones under the weight of a light Tonka toy car.

The assumption of *no* axle (Why does Eudora insist that this be spelt
"axal"?) friction is an idealism.

So we are to consider an object rolling and accelerating downhill on a
rough, wooden, flat, inclined plane and under the influence of gravity only
(no supercharged engine or axle friction) and construct a free body diagram.
Well, in the ideal case and in the lab (inertial) frame the tires will
rotate and accelerate therefore must have an applied force. That force must
be uphill. If the wheels are massive, the force must do conservative work.
Why do I feel hard pressed to call that force friction?

But Lowell also wants to include taped non-rotating tires. It isn't clear
if he wants to consider the coefficient of friction between tape (or tire)
and wood. If so, then obviously there is kinetic friction uphill.

If rolling friction is considered, it is sort of static and uphill.

The difficulty I have is in the possible kinetic axle friction. I would
certainly change the tangential force on the tires. The result will be to
decrease the acceleration of car and tires, therefore it would be static (as
the tire doesn't skid) and *downhill* on the tire.

But I am not at all convinced that I understand the question.




Jim.Green@Snow.edu


Hey, let's have some new cliches.