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Re: operational F, m, and a



John Denker said: If you define F in terms of ma, then F=ma becomes a
tautology. That means it becomes impossible in principle to even imagine an
experiment to determine how accurately F equals ma. It becomes impossible
in principle to design an experiment to check for small violations of the
F=ma law.

I am still trying to decide whether I think that is really a problem or not.
But let's suppose it is. Don't we have exactly the same problem with the
spring scale (fish scale) with the tautology F=kx?

If we defined F=Gmm/r^2 then wouldn't that become the tautology.

* * * *
Same subject... different line of thinking. This question is operational in
nature. One criticism about F=ma is it isn't always correct, i.e. when
relativity comes into play. But F=kx suffers a similar problem... not from
relativity, but from non-linearity in the spring, especially as we approach
the elastic limit. If F=kx is not totally true, how do you rule your scale,
or is the scale only valid at just one position? If we do rule the scale,
say every 0.1 N from 0 to 10 N, and we do this in a linear fashion, how
would we ever know if it is correct? Note, if people try to answer this
question I believe we should disallow hanging masses from the scale because
then we would really be using the weight approach to defining force rather
than the spring-scale approach.

Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817