(I send this again because I noticed how looong
the lines of this posting appeared to be in the
Phys-L archives. Hit the delete button if you already
got this in a readable form)
Hello all,
I haven't had a chance yet to read the Swartz
letter so I can't comment that. However,
there are some sources which might be
useful in analysing work done by friction.
Firstly, Arons (1997, 150-153) discusses a block accelerated from rest along a floor or a table
against by an applied force against a force of sliding friction. Arons then analyses the motion in
terms of Newton's second law and conservation of energy.
He points out that
"...we *cannot* calculate the work done by frictional
force at the interface. What happens at the
interface is a very complicated mess: We have abrasion, bending of 'asperities', welding and
unwelding of regions of 'contact', as well as shear stresses and strains in both the block and the floor."
Of course, you should read the whole discussion
to see his argument. Arons also makes
a reference to the paper by Sherwood and Bernard (1984)
for more details on work, heat and sliding friction.
Secondly, Swartz & Miner (1998, 203-204) discuss
briefly why negative work is - in their opinion –
a useless concept in an introductory level physics
(they also state that it is not needed in
more advanced treatments either). They consider
a box being pulled along a floor at constant speed.
Their point is that "The person (or agent) doing
the positive work needs fuel since work is a transfer
of energy. When in doubt, figure out who gets the fuel."
After reading Swartz & Miner's book I have
no doubts whatsoever regarding Swartz's
command of physics (and the same goes certainly
with Arons!). This does not mean to me, however,
that all Swartz's presentations would
be easily applicable to teaching introductory
(or high school) physics.
Best regards,
Antti
Antti Savinainen, Ph.D.
Senior Lecturer in Physics and Mathematics
Kuopio Lyseo High School
Puijonkatu 18
70110 Kuopio
FINLAND
E-mail: antti.savinainen@kuopio.fi
Web site: <http://kotisivu.mtv3.fi/physics/>
References:
Arons, A. (1997). Teaching introductory physics.
USA: John Wiley & Sons.
Sherwood, B.A. and Bernard, W.H. (1984). Work and heat transfer in the presence of sliding friction.
Am.J.Phys. 38, 450.
Swartz, C.E. and Miner, T.D. (1998). Teaching introductory physics - a sourcebook. USA:
AIP Press, Springler-Verlag.