Chronology | Current Month | Current Thread | Current Date |
[Year List] [Month List (current year)] | [Date Index] [Thread Index] | [Thread Prev] [Thread Next] | [Date Prev] [Date Next] |
And there is a *genuine* point of departure. I stand by everything I
have written in this thread and am content now to leave it to others
to judge the merits of the arguments that have been put forward.
John Mallinckrodt
> JD has suggested (correctly that the various parts of the boater do
work *on other parts of the boater*. That is, of course, correct.> by part b on part a.
But if one adds up all of *those* works (using the definition of work
given above) to get the "total work done by the boater", one will find
that the result is zero. This is because the work that any part a
does on any part b is necessarily equal and opposite to the work done
There's a law that says that the forces are equal and
opposite. But work is not equal to force. There's a dx
involved, and the dx is commonly very different.
Example: Suppose I start at rest and then start waving my
hand around in a circle. Suddenly I've got KE that I
didn't have before. By the work/KE theorem, the total
work (summed over the various parts) is nonzero.
I agree with JohnD. Yes indeed JohnM's approach of using the idea of
pseudowork seems to me to be quite unnecessary. Each time the ice skater
problem comes up, I get out JohnM's work paper and try to get some help out
of it. I am still trying. But I keep the reprint. <g>
Especially for intro students, W=dKE ought to be enough, if the various
systems are broken down appropriately.
Jim Green