Re: Friction

[palmer@sfu.ca (Leigh Palmer)]

> If I read the above paragraph correctly, am I to conclude that slipping
> friction (kinetic) is always greater than static friction?  Balderdash.

No, it's not. Sometimes it is. It is velocity dependent and depends also
on other factors, including contact area. It cannot be modelled well by
F = mu * N, where mu is independent of everything else.

Why reject a physical example just because it does not conform to your
lesson plan? I think that's what leads my students to disbelieve physics
describes the real world, and you reinforce that impression when you, in
the position of their teacher, simply deny facts.

Fact: tires on pavement are not well modelled by F = mu * N. If you must
teach this formula point out that it is a crude model used mostly for
obtaining rough ideas of behaviour of the frictional force, and it is
inapplicable to some situations, notable among these, tires on pavement.

Leigh