Thermodynamics

Thermodynamics:
The study of the relationship between heat, work, temperature, and energy,
encompassing the general behavior of physical system is called thermodynamics.
The first law of thermodynamics is often called the law of the conservation of energy
(actually mass-energy) because it says, in effect, that when a system undergoes a
process, the sum of all the energy transferred across the system boundary--either as
heat or as work--is equal to the net change in the energy of the system. For example, if
you perform physical work on a system (e.g. stir some water), some of the energy goes
into motion, the rest goes into raising the temperature of the system.

The second law of thermodynamics states that, in a closed system, the entropy
increases. Cars rust, dead trees decay, buildings collapse; all these things are examples
of entropy in action, the spontaneous movement from order to disorder.

Classical or Newtonian physics is incomplete because it does not include irreversible
processes associated with the increase of entropy. The entropy of the whole Universe
always increased with time. We are simply a local spot of low entropy and our destiny
is linked to the unstoppable increase of disorder in our world => stars will burn out,
civilizations will die from lack of power.
The approach to equilibrium is therefore an irreversible process. The tendency toward
equilibrium is so fundamental to physics that the second law is probably the most
universal regulator of natural activity known to science.
The concept of temperature enters into thermodynamics as a precise mathematical
quantity that relates heat to entropy. The interplay of these three quantities is further
constrained by the third law of thermodynamics, which deals with the absolute zero of
temperature and its theoretical unattainability.
Absolute zero (approximately -273 C) would correspond to a condition in which a
system had achieved its lowest energy state. The third law states that, as this minimum
temperature is approached, the further extraction of energy becomes more and more
difficult.