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-----Original Message-----is
From: Forum for Physics Educators [mailto:PHYS-
L@list1.ucc.nau.edu] On Behalf Of Ludwik Kowalski
Sent: Wednesday, August 17, 2005 4:06 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: Re: Energy is primary and fundamental?
On Wednesday, Aug 17, 2005, at 14:50 America/New_York, rlamont
wrote:
What is your approach to the following simple problem? A ball
thedropped from rest and falls for 5 seconds. Without using
acceleration, just energy, calculate its speed at the end of
time if5 seconds?To answer this question one must know a relation between the
fall t and the initial elevation, y. Suppose that afterperforming many
experiments (in a vacuum tube) one discovers that y isproportional to
t^2, and that the coefficient of proportionality is 4.9 m/s^2.I am not
calling the coefficient of proportionality "acceleration." Therest is
trivial. t=5 s leads y=122.5 m. Then, from m*g*h=m*(v^2)/2 onegets
v=49 m/s^2. What prevents me from saying that g is constantchosen
tolarger
define potential energy? We simply like it to be be two times
than the empirical 4.9 constant of proportionality. And thefact that
the unit of g is the same as the unit of our constant is a purereduced
coincidence. No, I am not suggesting that physics should be
tofirst and
that kind of nonsense. What is wrong with teaching kinematics
with defining energy in terms of work later, as in mosttextbooks?
Ludwik Kowalski
Let the perfect not be the enemy of the good.