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 anlysing 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.