KE & P

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2 total messages Started by Robert J. Devantery Fri, 01 Jul 1994 02:54

#1371

Author: Robert J. Devantery
Date: Fri, 01 Jul 1994 02:54

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I have been having a discussion of the conceptual explainations of energy and
momentum with some other physics teachers.  No one seems to be able to put
into words the "conceptual differences" between these two quantities.
We all resort to the mathematics to describe them.  One is a vector, one
is a scalar, etc.
Does anyone have a way of describing the difference between these to students?

Thanks,
Bob Devantery
New Hampshire

Re: KE & P

#1380

Author: Joe Bellina
Date: Tue, 05 Jul 1994 22:23

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I think there are real discussable conceptual differences between this two
quantities.  Momentum has a special significance because of its role in
Newton's second law...it enables us to determine whether or not a net force
is acting on an object.  If its momentum changes when viewed from an
inertial frame, then it has experienced a force and we need to look about
and see what the origin of that force might be.  The same cannot be said
for KE.  IF we only considered the KE we could run into a problem. 
Consider for example the case of uniform cirular motion.  If we only
considered KE we would conclude that no force was acting on the object
since the KE was not changing.  That in turn lead to the rejection of the
gravitational force when considering planetary motion.

Now I grant you, I have appealed to the vector nature of momentum, but have
not done so explicitly...is that conceptual enough?

Enjoy

In article <00980BEB.0A6DAE40.10@mentor.unh.edu>, "Robert J. Devantery"
<r_devantery@MENTOR.UNH.EDU> wrote:

> I have been having a discussion of the conceptual explainations of energy and
> momentum with some other physics teachers.  No one seems to be able to put
> into words the "conceptual differences" between these two quantities.
> We all resort to the mathematics to describe them.  One is a vector, one
> is a scalar, etc.
> Does anyone have a way of describing the difference between these to students?
> 
> Thanks,
> Bob Devantery
> New Hampshire

-- 
Joseph Bellina (jbellina@saintmarys.edu)

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