Re: CONSERVATION OF ENERGY

[LUDWIK KOWALSKI <kowalskil@alpha.montclair.edu>]

This long thread was started as a discussion on energy at the ASU workshop 
for high school physics teachers. Two teachers, (A) and (B), were talking:
...........................................................................
(A) Suppose that a puck, pushed along a horizontal floor with the initial 
    kinetic energy K comes to rest. It is stopped by a constant frictional 
    force, R. The sliding distance, x, should be

                              x = K / R

(B) This can not be exactly correct because part of the initial kinetic 
    energy is converted into thermal energy (temperature goes up). The 
    value of x should be less than K/R. 
...........................................................................

Thinking about this part of the dialog I would like to ask some questions. 
Is it not true that by writing K=R*x (A) is effectively saying that 'the 
kinetic energy is converted into work'? But work is not a form of energy. 
In the spirit of the first misconception (heat and work are forms of energy) 
let me say that 'in this situation first K is converted into work then work 
is converted into heat. Thus both work and heat are equal to K. Didn't we 
learn that conversions of W to Q can often be 100% efficient?'.

A clever student could suggest an experiment (an iron cube and an iron
plate, as in our situation) with a very sensitive thermometer to measure
dT. Once dT is known, he sugests, the c*m*dT can be calculated. And he
predicts that this triple product will be equal to K, which can also be
determined from experimental data (K=m*v^2/2). He knows how R can be 
calculated from the coefficient of kinetic friction and predicts that 
R*x=K. He asks me to measure x and verify his prediction that x=K/R.

Now suppose I follow this advice and find out that both of his predictions
are confirmed. Do not jump, I am not saying this will happen. Just pretend 
it happens and tell me if this would be an 'experimental verification' of 
the mental picture according to which K-->Work-->Heat. If your answer is
positive then we may agree that the above sequence of transformations is 
experimentally testable. We can anticipate an experiment which can possibly 
falsify the idea that work and heat are forms of energy. 

What I really want to know is this. Do we say that the idea (K-->W-->dU) 
is nonsensical (a misconception, if you wish) because it does not agree 
with other formal definitions, or do we say it is nonsensical because it 
is in disagreement with experimental facts?
...........................................................................

A textbook I am using tells kids that a hypothesis, such as 'science is 
permeated with an undetectable essence', is not scientific unless there 
is a test for a possibility of its wrongness. Sometimes I think that W 
and Q belong to undetectable essences. On July 23 David Dockstader wrote:

> Don't forget that physics is based on observation too. I maintain that
> science is the fine art of model making. We make observations and then 
> try to model the observations. 

A hypothesis, K-->W-->Q, is a mental model. It is based on observations
we make with thermometers, speedometers and rulers. Is it verifiable or 
not? Is it scientific or not? Is it correct or not? Why yes? Why not?

                                                   Ludwik Kowalski