Hi again Michael,

Unfortunately, I haven't been following this thread. Did the original
poster want to know how to compute area expansion from linear expansion, or
did they want to know what the relationship between the defined linear and
area coefficients of expansion? I had guessed (perhaps incorrectly) that it
was the former that they wanted. In other words, they had a practical
application where they knew alpha for a material and wanted to know how
much it would expand in area. (I admit, though, that in most circumstances
this is splitting hairs since the alpha^2 term would be so small).

Sean

At 01:00 PM 9/28/01 -0700, you wrote:
By definition, all the coefficients of thermal expansion (whether for
>length, area, or volume) are for linear changes. Same idea as
>resistance, where the definition is V = I R, whether or not the
>potential actually varies linearly with the current; in cases where
>the variation *is* (to a good enough approximation) linear, R is a
>constant and is called the resistance. The derivation I gave is
>correct, because the coefficients are *defined* for the linear regime
>(in which change in size is proportional to change in temperature).
>In that regime, the coefficient of area expansion is exactly 2 times
>the coefficient of length expansion.
>
>Nonlinear effects can also be treated, of course, to as high an
>order as you need to go to get the precision that you need.
>
>Michael
>
>Thank you for reading my little posting.
>
>
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