01
Dec
07

Just to Clarify

secondlaw.gifBill Bryson, in A Short History of Everything, includes a section on most major fields of scientific inquiry, and makes them accessible to us amateurs. In a section on the laws of thermodynamics, here’s how Bryson clarifies each law for us (except the zeroth, which states, “If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.”

First law:
“for a thermodynamic cycle the sum of net heat supplied to the system and the net work done by the system is equal to zero”

Bryson translation:
you can’t create energy

Second law:
“The
entropy of an isolated system not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium”
Bryson translation:
a little energy is always wasted

Third law:
“As temperature approaches absolute zero, the entropy of a system approaches a constant”

Bryson translation:
you can’t reduce temperatures to absolute zero – there will always be some residual warmth

To be certain we understand how these laws came about, Bryson quotes the following from P. W. Atkins:

There are four Laws. The third of them, the Second Law, was recognized first; the first, the Zeroth Law, was formulated last; the First Law was second; the Third Law might not even be a law in the same sense as the others.

If only they’d have made it this clear when I was in school.


1 Response to “Just to Clarify”


  1. 1 LoriCatherine
    December 3, 2007 at 4:47 am

    I kind of sort of understand this somewhat completely……only because I was previously married to an engineer! Thanks for the smile!


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