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[Phys-l] d ln V / d ln P = ??



Hi Folks --

This is mostly a terminology question.

By way of background: the quantity

- ∂ P |
Ks = ------ | [1]
∂ ln V |S

is called the adiabatic bulk modulus, and its inverse is call
the adiabatic compressibility. It is common but sloppy to call
them "the" bulk modulus and "the" compressibility.

Reference: http://en.wikipedia.org/wiki/Bulk_modulus

So the question is, what do we call the quantity

- ∂ ln P |
? = -------- | [2]
∂ ln V |S

It is obviously dimensionless.

For ideal gases, it is equal to the adiabatic index i.e. the
ratio of specific heats i.e. γ .... We don't need a new
name for that; there are more than enough names already.

On the other hand, for water at 1 atm, the ratio of specific
heats is close to unity, whereas the dimensionless modulus
in eq. [2] is 22000 times greater than that.

If it helps, note that I am actually more interested in the
compressibility-like quantity

- ∂ ln V |
?? = -------- | [3]
∂ ln P |S

Is there a conventional name for either of [2] or [3], and/or
can anybody suggest a nice name?