Re: [Phys-l] Collision of irregular bodies

["Bob LaMontagne" <rlamont@postoffice.providence.edu>]

A tautology - yes - but a very difficult concept for students to believe. In
second semester general physics classes we claim that the electric field
near a conductor must be perpendicular to the surface because the
free-to-move electrons will not allow a tangential field to develop. The
students then do field mapping in lab and most of them cannot give a good
conceptual reason why the field lines are perpendicular. Even those who
state the correct reason on the lab sheets get tripped up if you start
discussing it with them.

Bob at PC

> -----Original Message-----
> From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
> bounces@carnot.physics.buffalo.edu] On Behalf Of John Denker
> Sent: Friday, August 11, 2006 7:41 PM
> To: Forum for Physics Educators
> Subject: Re: [Phys-l] Collision of irregular bodies
>
> R. McDermott wrote:
> > In the absence of tangential effects (friction or an equivilent)
> wouldn't
> > any forces have to act perpendicularly to the surfaces at the point of
> > contact?
>
> That sounds like a tautology:  In the absence of tangential forces,
> what remains is the normal force.  By definition, n'est-ce pas?
>
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