Re: work done by friction

[Leigh Palmer <palmer@SFU.CA>]

> Leigh,
> I have not analyzed this in detail, but let me open a possible solution
> to any apparent energetic paradox:

I don't think there's an energetic paradox in what I posted; I did
not intend it as such anyway. It is an example to show that it takes
sophistry to extract the correct amount of "work" from sliding
friction. Clearly the product of the force we call friction and the
distance over which it acts are the same on both sides of the
collision I analyzed, and clearly the "amount of work" is the same,
or it must be rationalized irrationally to be shown to be different.
Clearly a student couldn't usefully employ this concept.

> Perhaps this is another example of an interaction in which the system as
> defined must lose energy to the environment.
>
> Also, I see nothing in your calculation that the requires that the force
> of interaction be friction - it could be any mechanism.  Perhaps you are
> showing that that mechanism (even if friction) must involve a
> dissipation of energy to the surroundings. (recall the "capacitor
> conundrum").

The force is friction by hypothesis; I didn't say that any other
force couldn't do the same thing. What I envision is two bricks
which suffer a glancing collision, one rubbing against the other.
I make no pretense that this is the only place where work is an
ill-suited concept to be applied to the analysis.

Leigh