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]

Re: [Phys-l] teaching energy



On Mon, 2 Oct 2006, Bob LaMontagne wrote:

OK - given:

A) In the classroom:
Book on high shelf = high potential energy.
Book on lower shelf = lower potential energy.

How does height become magically transformed to motion? Height and motion
are entirely different entities. It's actually the gravitational force
producing the change in KE. PE only provides a convenient calculational tool
that allows the student to easily compute the change in KE when the
elevation of the object changes and gravity is the only force involved. To
me, that is the essence of energy - a scalar calculational tool that acts as
a very convenient surrogate for Newton's 2nd Law. I find it ill conceived to
encourage a student to somehow turn potential energy into some kind of a
substance that can (with the proper incantations) magically appear as KE.

OK, that's your bias, and you're entitled to it. But why do you insist that your students have tha same bias? Later on, some of your students will discover that they don't have to start with Newton's laws, but can choos something called "action" as a fundamental starting quantity. I would take the "only" out of your sentence starting with "PE". Then each of your students will deal with PE in a manner moast concvenient to that student. On some days I see PE as a shimmering yellow-orange glow, which looks to me like "some kind of a substance". Are you telling me that after all these years and all those papers I have to change the way I think about PE? But please don't assume that I would ever impose my picture of PE (as I see it on a particular day) on a student.
Regards,
Jack



Energy conservation can be presented as simply an equation that solves
motion problems in a path independent form. The mental image of something
transforming to something else is extraneous and prone to a mystical
interpretation of physics. I'm not advocating eliminating teaching energy -
just don't reify it.

I'll shut up at this point because I realize this topic has been talked to
death in the past and is probably boring the socks off most readers

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: Saturday, September 30, 2006 8:05 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] teaching energy

On 09/30/2006 05:44 PM, Bob LaMontagne wrote:

Potential energies, on the other hand, are way of easily calculating how
a
conservative force will change a KE if an object changes position. That
is
difficult, if not impossible, for a student to associate with a concrete
image.

A) In the classroom:
Book on high shelf = high potential energy.
Book on lower shelf = lower potential energy.

B) Student pilots have an _easier_ time estimating their height (PE)
than their airspeed (KE).

_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l

_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l


--
"Trust me. I have a lot of experience at this."
General Custer's unremembered message to his men,
just before leading them into the Little Big Horn Valley