Second law of Thermodynamics

The second law is a straightforward law of physics with the consequence that, in a closed system, you can't finish any real physical process with as much useful energy as you had to start with — some is always wasted. This means that a perpetual motion machine is impossible. The second law was formulated after nineteenth century engineers noticed that heat cannot pass from a colder body to a warmer body by itself.

According to philosopher of science Thomas Kuhn, the second law was first put into words by two scientists, Rudolph Clausius and William Thomson (Lord Kelvin), using different examples, in 1850-51. American quantum physicist Richard P. Feynman, however, says the French physicist Sadi Carnot discovered the second law 25 years earlier. That would have been before the first law, conservation of energy, was discovered! In any case, modern scientists completely agree about the above principles.

Second Law: Entropy
Second Law of Thermodynamics: In any cyclic process the entropy will either increase or remain the same.

Entropy: a state variable whose change is defined for a reversible process at T where Q is the heat absorbed(deltaS=Q/T).
Entropy: a measure of the amount of energy which is unavailable to do work.
Entropy: a measure of the disorder of a system.
Entropy: a measure of the multiplicity of a system.

Since entropy gives information about the evolution of an isolated system with time, it is said to give us the direction of "time's arrow" . If snapshots of a system at two different times shows one state which is more disordered, then it could be implied that this state came later in time. For an isolated system, the natural course of events takes the system to a more disordered (higher entropy) state.

previous page::next page