What does it mean?
The second law of thermodynamics can be simply decomposed into four profound statements (referenced from hyperphysics).
- "Heat will not flow spontaneously from a cold object to a hot object."
- Any system which is free of external influences becomes more disordered with time. This disorder can be expressed in terms of the quantity called entropy.
- "You cannot create a heat engine which extracts heat and converts it all to useful work."
- "There is a thermal bottleneck which constrains devices which convert stored energy to heat and then use the heat to accomplish work. For a given mechanical efficiency of the devices, a machine which includes the conversion to heat as one of the steps will be inherently less efficient than one which is purely mechanical."