2nd Law of Thermodynamics

Heat, being a form of energy, is subject to the principle of energy conservation discussed in the last chapter. In the context of heat energy, this principle is called the 1st law of thermodynamics:

By ``closed'', we mean a system that is completely cut-off, or insulated from its surroundings, so that no material or energy enters or leaves.

Also as discussed in the last chapter, heat, being a form of energy, can be transformed into work and other forms of energy, and vice versa. However, this transformation of heat energy is subject to a very important restriction, called the 2nd law of thermodynamics. This law is in fact necessary to resolve the following apparent paradox:

$\parbox{4.5in}{\vspace*{5pt} If you place an ice cube outside on a ... ...unding air warmer. Why then doesn't this latter phenomena occur? \vspace*{5pt}}$

The answer lies in the statement of the 2nd law of thermodynamics, which can be given in three equivalent forms:

When phrased in a precise mathematical language, one can show that any one of the forms of the 2nd law imply the other two. We shall discuss each of these three forms in turn.