Re: Favorite Test Questions

[Jerome Epstein <jerepst@worldnet.att.net>]

> Like most of your students, I am also having difficulty answering
> the above question. According to my dictionary and most physics
> textbooks, static refers to forces exerted on bodies at rest.
> As the racers leave the starting line, both the wheels and the
> rest of the racing cars are in motion. thus, static friction would
> not apply at all to the situation as described.

The point of contact between tire and road is static unless the wheels
are slipping. The fact that the car is moving is irrelevant. The
surfaces in contact are momentarily at rest with respect to each other.
Static friction applies (you hope -- else you are out of control).
J. Epstein

> The spinning wheels AT THE STARTING LINE undergo kinetic
> friction from the time that they start spinning until that race car
> comes to a full stop at the end of the drag race.
I'm afraid this is just not true.

J. Epstein