Re: FRICTION

[Brian McInnes <bmcinnes@PNC.COM.AU>]

Ludwig wrote
> According to an old book on electrostatics the coefficient of
> kinetic friction is not always proportional to the load, N. For
> Al on steel f=mu*N for any N (mu=1.2). But for Cu on Cu this
> is true only when the load is due to at least 100 grams (mu=1.8).
> Below this: mu=0.4 at 0.1 grams, 0.7 at 1 gram and 1.5 at 10 grams.
> Reading from the graph (a lot of data points and a smooth line )

While I was reading this e-mail from Ludwig, I was thinking, well, I wonder
what my "authority" on friction  has to say about this.  When I checked my
"authority" I found the very figures you were quoting.  It was then I
realized how quickly the years are passing by,  My "authority" Bowden and
Tabor's seminal work on friction, Friction and Lubrication, Methuen, 1956,
has now become Ludwig's "old book".  Never mind, that does not detract from
its status as one of the best texts written on experimental and applied
physics in general and friction and lubrication in particular.  It was
referred to recently by David Marx. I recommend the book to all.

Another formative contribution to my ideas about friction was Feynman's
comments that measurements of coefficients of static friction were really
measurements of friction coefficients between greasy and/or dirty surfaces.

Finally, in connection with friction, may I remind people of Eric Rogers'
beautiful exposition of the "demon" theory of friction where, in his book,
Physics for the Inquiring Mind, he demonstrated the versatility of ad hoc
theories.

Brian McInnes