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Re: Why work before energy in texts



There appears to be two or three threads on this subject -- which, with my poor
memory, makes it difficult.

I mistakenly thought the argument was which to use first in an intro text i.e..
HS w/ at most algebra. Many posts talk about integrals, etc. It was my
assumption that it was "bone head" physics, and that is why I suggested what was
kinesthetic be intro'd first i.e. pushing a lawn mower and Mgh, next KE and
springs.

bc

P.s. Hewitt claims that the concept of energy was unknown to Newton, and its
existence was debated up to the 1850's. Springs are too difficult at the level of
the text I have. PSSC begins with work and KE then to PE (including the spring,
but then it went the way of the Berkeley Physics Course.





Joseph Bellina wrote:

I just check Frank, the predecessor to Sears...its work before
energy. Then I check Jeans 1907 Theoretical Mechanics, its work before
energy.
Lindsay and Margenau, Foundations of Physics, Wiley 1936 has
an interesting section...I refer you to pages 120 to 128, a section
called The Concept of Energy.
They claim that the concept of energy goes back to Galileo, and the
concept of work comes from later discussions revolving around the notion
that forces are not applied in instants, but rather over time or during
a change in position..so what might the aggregate affect be.

Part of this is my interpretation...so you might want ot read the
original...or not.

cheers,

joe

On Fri, 12 Oct
2001, RAUBER, JOEL wrote:

Just a few comments:

Ludwik has asked some good questions in his recent post, about the energy
first approach.

It is my impression that the vast majority of popular introductory level
books present Work first, energy second. I'm sure they and the authors do
it for a reason; even if it is only for the bad reason of pedagogical
inertia; but I suspect it is more than that. Do any folks on the list have
opinions why Work first is the approach of the vast majority of texts? Even
the PER based text by Reif is essentially a Work first approach (Work and
Kinetic Energy introduced simultaneously and Potential energy later.

For those interested in a text that does do what John D suggests, check out
the "Physics 2000" "text". The author proceeds rather closely to how Ludwik
outlines things; I haven't read yet how he handles springs and 1/2*K*X^2 for
spring potential energies.

Last minor point. I don't think Ludwik's worry about students not being
able to "multiply vectors" (by which I assume he means the dot product of
vectors) is a problem. There exist texts that teach that early on, well
before week 5.

I personally don't like that approach of an opening chapter that does vector
algebra along with dot and cross products. But it is done in a minority of
texts. I prefer to introduce the dot and cross products as needed.

Joel R


Joseph J. Bellina, Jr. 219-284-4662
Associate Professor of Physics
Saint Mary's College
Notre Dame, IN 46556