Thermodynamics, << `thur` moh dy NAM ihks, >> is the study of heat and other forms of energy. It is also the study of the conversion of energy from one form into another. Engineers, chemists, and physicists use the principles of thermodynamics to understand events in nature. They also use them in such activities as designing machines and calculating the loss or gain of energy in a chemical reaction.
Thermodynamics is based chiefly on three scientific rules called laws. The first law states that energy cannot be created or destroyed. Instead, energy is either converted from one form into another or transferred from one system to another. In thermodynamics, a system may be anything from a simple object to a complex machine. For example, the engine in an automobile is a thermodynamic system called a heat engine. A heat engine changes the energy stored in a fuel into thermal energy. Thermal energy is commonly referred to as heat. A heat engine then converts the thermal energy into mechanical energy. This energy does useful work, such as making the car move. The thermal energy inside the system, called internal energy, also undergoes certain changes. But no matter what form energy takes, the total amount of energy always remains the same.
The second law of thermodynamics deals with the natural direction of energy processes. According to this law, for example, thermal energy will flow only from a hotter object to a colder object. The second law of thermodynamics accounts for the fact that a heat engine can never be completely efficient. This fact means that a heat engine cannot convert all the energy stored in fuel into useful work. Instead, the engine transfers some of that energy to colder objects in its surroundings, in a process called heat transfer.
The third law of thermodynamics concerns the concept of absolute zero. Absolute zero is the theoretical temperature of a system with no thermal energy. The third law states that it is impossible to reduce the temperature of any system to absolute zero.
Thermodynamics can also be used to explain why some machines cannot work. For example, dreamers have long searched for a machine that would operate continuously without any input of energy. Such a machine is called a perpetual motion machine. One type of perpetual motion machine would essentially create energy, violating the first law of thermodynamics. Likewise, an engine that converts all of its fuel into useful work with no loss of energy is a perpetual motion machine that would violate the second law.
