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Re: The drag force -- a correction squared



I wrote at some point down a side-alley:

... I can show it is ABSOLUTELY TRUE that the population
of Sri Lanka is strongly correlated with the change in US Stock
market values over the last six or seven years. It is not only
perfectly correct, and quite clear as I stated it, but totally
misguided in terms of causality, in fact!


At 20:40 10/7/00 -0400, Ludwik responded:
Two comments:

1) Cause and effect is a big and profound issue.
Are we trying to avoid it in physics?

2) The ABSOLUTELY TRUE above is meaningless unless
the "strongly correlated" is declared. It may be
true if "strongly" means r>0.8. But it is not
likely to be true if "strongly" means r>0.99.

Unlike in psychology, r>0.99 are quite common in physics. For
example, when we plot measured values of terminal speeds versus
masses of falling objects. Or when we plot amps versus volts (for
a wire at room temperature), etc.
Ludwik Kowalski


Two comments in response.
1) A high school teacher expressed his unease with a text book
that purported to show a relation between drag force and the
product of mass and velocity.

There was one contribution to his question which was responsive.
It was mine.
The remaining efforts leave me in no doubt at all why HS teacher
discussions particularly from women are relatively scarce here -
the contributions do not respond to the original question.

2) I seem to recall that Ludwik aired some difficulties with his
interpretation of nuclear decay statistics, and some difficulties
with plotting a ballistic curve realistically, in previous threads.

Is it reasonable for him to take me to task for using the
scientifically descriptive "strong correlation" phrase while he
remains silent on another contribution confirmed in several posts,
that one physical measure is proportional to another?

Do I HAVE to explain that such a bald statement implies PERFECT
correlation, unless qualified? Do physics teachers really think
that any of their experimental results demonstrate perfect
correlation?
That is the realm of the sleight of hand arithmetician, not the
experimentalist, in my (always humble) view.


brian whatcott <inet@intellisys.net> Altus OK
Eureka!