DEFINITION OF THERMODYNAMICS

Thermodynamics is the study of the

transformation of heat into and from other forms of energy. It

forms the basis of many principles of chemistry, physics, and

earth sciences. The First Law of Thermodynamics states that

energy can be neither created nor destroyed, and that heat and

mechanical work are mutually convertible. The Second Law

of Thermodynamics states that it is impossible for an unaided

self-acting machine to transfer heat from a low-temperature

body to a higher-temperature body. The Third Law of Thermodynamics

states that it is impossible to reduce any system

to absolute zero temperature (0°K, ¯273°C, or ¯459°F).

Energy is the capacity to do work, and it can exist in

many different forms. Potential energy is energy of position,

such as when an elevated body exhibits gravitational potential

in that it can move to a lower elevation under the influence

of gravity. Kinetic energy is the energy of motion and

can be measured as the mean speed of the constituent

molecules of a body. Einstein’s Theory of Relativity showed

that mass too can be converted to energy, as E = mc2, where E

= energy, m = mass, and c = the speed of light. This remarkable

relationship forms the basis of atomic power and many

mysteries of the universe.

Heat is a form of kinetic energy that manifests itself as

motion of the constituent atoms of a substance. According to

the laws of thermodynamics, heat may be transferred only

from high-temperature bodies to lower-temperature bodies,

and it does so by convection, conduction, or radiation. The

specific heat of a substance is the ratio of the quantity of heat

required to raise the temperature of a unit mass of the substance

through a given range of temperature to the heat

required to raise the temperature of an equal mass of water

through the same range.

Conduction is the flow of heat through a material without

the movement of any part of the material. The heat is

transferred as kinetic energy of the vibrating molecules,

which is passed from one molecule or atom to another. Convection

is the transfer of heat through a fluid (liquid, gas, or

slow-moving solid such as the Earth’s mantle) by moving currents.

Radiation is a heat transfer mechanism by infrared

rays. All materials radiate heat, but hotter objects emit more

heat energy than cold objects. Infrared radiation can pass

through a vacuum and operates at the speed of light. Radiative

heat can be reflected and refracted across boundaries but

does not affect the medium through which it passes.

See also MANTLE.

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