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F=m*a, was Thermodynamics



Here is a similar (?) situation. If the speed of light in empty
space is DEFINED as 299,792,458 m/s (as in SI since 1983)
then measuring c makes no sense. On the other hand, if we
define distance and time as "what we measure with instruments"
then an experimental determinations of c=d/t makes sense.
Is this a good analogy of the situation encountered in F=m*a?
Ludwik Kowalski

"John S. Denker" wrote:

At 09:41 AM 8/30/01 -0400, Hugh Haskell wrote:

"There is no reason to expect that an object will have any one particular
acceleration given a certain force. When the acceleration of the object is
measured, however, we find that it obeys a law of the form a = F/m."
I would say that this would be true only if one has definitions of
both force and mass that do not involve acceleration in any way.
I don't think any exist.
In fact, we use the above relationship to identify forces.

Then at 10:51 AM 8/30/01 -0400, I disagreed.

Here is a shorter and perhaps clearer way of making my point. Suppose we
did use F = ma to define and "identify" forces. Then F=ma would be a
tautology. There would be absolutely no way, by definition, to find a
force that did not uphold the F=ma law.

But that is not the case. We _can_ define (F) and (m) and (a) in such a
way that it is possible to design experiments to test the F=ma law. For
homework: design a series of experiments to do this.

As Karl Popper explained, a theory (such as F=ma) that is falsifiable is
incomparably more important than one that isn't.