Re: momentum conservation(2)

[Robert A Cohen <bbq@ESU.EDU>]

Bob, thanks for the "action at a distance" example.  I think that
clarifies the students' conflict better.  It is common for students to
think "hmmmm...the forces are equal and opposite, and the displacements
must be the same...so the work done and thus the kinetic energies must be
equal and opposite (in sign)".  The "action at a distance" is a good way
to get them to examine their "displacements must be same" assumption
(although the way one defines "work done" also has to be addressed, as
pointed out by others).

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| Robert Cohen               Department of Physics       |
|                            East Stroudsburg University |
| bbq@esu.edu                East Stroudsburg, PA  18301 |
| http://www.esu.edu/~bbq/   (570) 422-3428              |
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On Tue, 14 Mar 2000, Bob Sciamanda wrote:

> Point well taken, Robert.
> But consider the non-contact interaction two charged point particles
> ("action at a distance").
> Perhaps the most basic, all-encompassing, requirement is that there be
> some mechanism for transformation of KE into other forms.  Such a
> mechanism is required even in an elastic collision (although in the
> elastic case the energy is finally returned to the particles as KE).
>
> ----- Original Message -----
> From: "Robert A Cohen" <bbq@ESU.EDU>
>
> > Perhaps it is better to say that the center of mass of each object may
> > travel a different distance through space?  After all, wouldn't the
> > contact point travel the same distance for both objects?