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Re: [Phys-L] dimensional analysis



Date: Wed, 25 Jul 2012 16:37:16 -0600
From: Larry Smith <larry.smith@snow.edu>
Reply-To: Phys-L@Phys-L.org
To: Phys-L@Phys-L.org
Subject: [Phys-L] dimensional analysis
> Seems to me that the term "dimensional analysis" is used in
> two different ways. Some sources use it to mean simply
> converting from one kind of units to another...
> What do you mean when you say "dimensional analysis"?

To me, "dimensional analysis" means to analyze the dimensions of the
relevant quantities involved in the problem. This is usually done to
infer the correct functional form of the answer. Dimensional Analysis
can let you estimate the numeric value of an answer without doing the
hard work of fully solving the real problem.

"Dimensional Analysis" does NOT mean units conversion. Units
conversion does not change the dimensions of any quantity, so there is
nothing to analyze. Units conversion is nothing but multiplying by a
dimensionless 1 written in a convenient form.

> Do the two uses fall along disciplinary lines (chemistry vs.
> physics)?

I'm a physicist, so take that as one data point. I've never heard
anyone use the term "dimensional analysis" when they meant "units
conversion" -- until now -- but perhaps I live a sheltered life.


_________________
Christopher M. Gould 213-740-1101 Dept. of Physics & Astronomy
gould@usc.edu Univ. of Southern California
http://physics.usc.edu/~gould/ Los Angeles, CA 90089-0484