# Meaning of "adiabatic" in Britain?

1. May 22, 2014

### George Jones

Staff Emeritus
I recently have discovered that the thermodynamics term "adiabatic" seem to be used slightly differently in Britain than it is in North America.

What does "adiabatic" mean in Britain?

2. May 22, 2014

### CAF123

I was not aware of any differences in the term. In the context of thermodynamics, an adiabatic process is one in which there is no heat transfer over the system/surroundings boundary. The Oxford dictionary has a similar definition, see http://www.oxforddictionaries.com/definition/english/adiabatic [Broken].

Where did you hear about a difference?

Last edited by a moderator: May 6, 2017
3. May 22, 2014

### George Jones

Staff Emeritus
I am curious about how folks will respond, so, in order not to bias responses, I am going to be coy for now, and not state what I have read, but I have seen the same thing twice, once in a grad-level text.

4. May 22, 2014

### D H

Staff Emeritus
This site, http://www.damtp.cam.ac.uk/user/tong/statphys.html, has lecture notes from David Tong's "introductory course on statistical mechanics and thermodynamics given to final year undergraduates." He appears to use "adiabatic" in two different ways in the fourth part of his lecture notes, http://www.damtp.cam.ac.uk/user/tong/statphys/four.pdf.

He defines "adiabatic walls" as something that completely isolates a system from all outside influences. Then he writes about adiabatic compression and expansion in terms of a Carnot cycle. Then he writes about adiabatic processes as ones that don't exchange heat with the environment. So far, so good. It appears that there is no difference between the word adiabatic in US and UK usage.

But then he writes about adiabatic surfaces where those in the US would use the word isentropic instead. It appears that a few other UK sites also use adiabatic where we would use isentropic.

5. May 22, 2014

### CAF123

There is a quantity of interest in oceanography called, confusingly, the adiabatic lapse rate defined as $(\partial T/\partial P)_S$ even though the thermodynamic derivative is isentropic or at constant entropy. Ofcourse, the latter term is more appropriate.

6. May 22, 2014

I've only ever heard it used one way among my American and British colleagues. Maybe it varies somewhat by field?

7. May 22, 2014

### D H

Staff Emeritus
IIRC, the adiabatic lapse rate is defined as $(\partial T/\partial z)_Q$, in other words, change in temperature with elevation given no heat transfer. (Compare the environmental lapse rate, $dT/dz$ in the "real" atmosphere.)

8. May 22, 2014

### George Jones

Staff Emeritus
I just found another reference ,

In his book "Cosmological Physics", John Peacock writes (Peacock's bold)

The other reference I had in mind was

In all of these, adiathermal seems to mean what I would call adiabatic, and adiabatic seems to mean what I call isentropic.

Last edited by a moderator: May 6, 2017
9. May 22, 2014

### WannabeNewton

In "Elements of Classical Thermodynamics for Advanced Students of Physics" by A.B. Pippard, who was a professor in Cambridge at the time the book was engendered (1957), the term adiabatic is used to refer to reversible adiathermal ($Q =0$) changes i.e. a quasi-static process for which $\delta Q = 0 \Leftrightarrow dS =0$. Pippard also writes in a footnote that "Some writers prefer to use adiabatic in the sense of our adiathermal, and to call our adiabatic change a reversible adiabatic or isentropic change." (p.31) so there do seem to be inconsistencies in the literature even amongst the British authors.

P.S. this is an amazing book on thermodynamics that you should definitely buy; it's quite cheap!

10. May 22, 2014

### D H

Staff Emeritus
Aha!

Here's a couple more textbooks and a journal article that use "adiathermal":

Blundell and Blundell, Concepts in Thermal Physics, Oxford University Press (2006).
McIlveen, Fundamentals of Weather and Climate, Oxford University Press (2010).
Callendar, "III. On the thermodynamical correction of the gas-thermometer." The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science 5:25 48-95 (1903).

11. May 22, 2014

### CAF123

That seems to be the same John Peacock who is a professor of cosmology at the university I attend. I guess one needs to specify how they are defining their terms. For example, with that reference of the adiabatic lapse rate, a piece of follow-up text was explaining that an adiabatic process is not necessarily isentropic. So clearly here they were meaning 'adiabatic' here to mean 'adiathermal' in the terms used in those books.

Last edited: May 22, 2014
12. May 22, 2014

### Philip Wood

A B Pippard’s Classical Thermodynamics (1957) is an acknowledged British classic. Here are the relevant passages…

"For any system, in an adiathermal process, i.e. one performed by means of work on an otherwise isolated system, ΔU = W." (1964 ed, p 16)

"[…] we shall be closely concerned with adiabatic changes, that is reversible adiathermal changes […]" (1964 ed. p 31)

But he says in a footnote…
"Some writers prefer to use adaiabatic in the sense of our adiathermal, and to call our adiabatic change a reversible adiabatic or isentropic change."

For the little it's worth, this is my own (British) preference. I never use the word 'adiathermal'. [Maybe I'm unconsciously following the usage in that great American textbook, M W Zemansky's Heat and thermodynamics!]

Etymology doesn't support a distinction: adiabatic means "doesn't go through" and "adiathermal" means "heat doesn't [go] through"!

Last edited: May 23, 2014