Re: Work/Energy Theorem

[SCIAMANDA@edinboro.edu]

> . . it is NOT necessary for an external agent to do work to accelerate
> an object. . .
>  A. John Mallinckrodt      email:  mallinckrodt@csupomona.edu

The word "work" is defined as the left hand side of the Work-Energy 
theorem (at least for me).  When that theorem is applied to a single 
particle, the work done by a force is the force integrated over the 
displacement of the particle.  Within this context, the above statement 
is true (if "object" means only a STATIONARY PARTICLE experiencing 
the force). 

When the theorem is applied to a system of particles,  the 
work done by a force is the force integrated over the displacement 
of the C.M. of the particle system.  Within this context, the above 
statement is false, and in fact it is ONLY the external forces that 
do net work.  Note that the displacement of the "point of 
application" of the force is irrelevant.

This may violate the conceptual model of work always involving 
a local transfer of energy, but it is what the mathematical model 
(the Work-Energy theorem) states.

Bob Sciamanda           sciamanda@edinboro.edu
Dept of Physics
Edinboro Univ of PA     http://www.edinboro.edu/~sciamanda/home.html