Thermodynamics - Key terms
ABSOLUTE ZERO:
The temperature, defined as 0K on the Kelvin scale, at which the motion of molecules in a solid virtually ceases. The third law of thermodynamics establishes the impossibility of actually reaching absolute zero.
BTU (BRITISH THERMAL UNIT):
A measure of energy or heat in the Britishsystem, often used in reference to the capacity of an air conditioner. A Btu is equal to 778 foot-pounds, or 1,054 joules.
CALORIE:
A measure of heat or energy in the SI or metric system, equal to the heat that must be added to or removed from 1 gram of water to change its temperature by 33.8°F (1°C). The dietary Calorie (capital C) with which most people are familiar is the same as the kilocalorie.
CONDUCTION:
The transfer of heat by successive molecular collisions. Conduction is the principal means of heat transfer in solids, particularly metals.
CONSERVATION OF ENERGY:
A law of physics which holds that within a system isolated from all other outside factors, the total amount of energy remains the same, though transformations of energy from one form to another take place. The first law of thermodynamics is the same as the conservation of energy.
CONSERVE:
In physics, "to conserve" something means "to result in no net loss of" that particular component. It is possible that within a given system, the component may change form or position, but as long as the net value of the component remains the same, it has been conserved.
CONVECTION:
The transfer of heat through the motion of hot fluid from oneplace to another. In physics, a "fluid" can be either a gas or a liquid, and convection is the principal means of heat transfer, for instance, in air and water.
ENERGY:
The ability to accomplishwork.
ENTROPY:
The tendency of natural systems toward breakdown, and specifically, the tendency for the energy in a system to be dissipated. Entropy is closely related to the second law of thermodynamics.
FIRST LAW OF THERMODYNAMICS:
A law which states the amount of energy in a system remains constant, and therefore it is impossible to perform work that results in an energy output greater than the energy input. This is the same as the conservation of energy.
FOOT-POUND:
The principal unit of energy—and thus of heat—in the British or English system. The metric or SI unit is the joule. A foot-pound (ft · lb) is equal to 1.356 J.
HEAT:
Internal thermal energy that flows from one body of matter to another. Heat is transferred by three methods conduction, convection, and radiation.
HEAT CAPACITY:
The amount of heat that must be added to, or removed from, a unit of mass of a given substance to change its temperature by 33.8°F (1°C). Heat capacity is sometimes called specific heat capacity or specific heat. A kilocalorie is the heat capacity of 1 gram of water.
HEAT ENGINE:
A machine that absorbs heat at a high temperature, performs mechanical work, and as a result gives off heat at a lower temperature.
KINETIC ENERGY:
The energy that an object possesses by virtue of its motion.
JOULE:
The principal unit of energy—and thus of heat—in the SI or metric system, corresponding to 1 newton-meter (N · m). A joule (J) is equal to 0.7376 foot-pounds.
KELVIN SCALE:
Established by William Thomson, Lord Kelvin (1824-1907), the Kelvin scale measures temperature in relation to absolute zero, or 0K.(Units in the Kelvin system, known as Kelvins, do not include the word or symbol for degree.) The Kelvin and Celsius scales are directly related; hence Celsius temperatures can be converted to Kelvins by adding273.15.
KILOCALORIE:
A measure of heat or energy in the SI or metric system, equal to the heat that must be added to or removed from 1 kilogram of water to change its temperature by 33.8°F (1°C). As its name suggests, a kilocalorie is 1,000 calories. The dietary Calorie (capital C) with which most people are familiar is the same as the kilocalorie.
MECHANICAL ENERGY:
The sum of potential energy and kinetic energy in a given system.
POTENTIAL ENERGY:
The energy that an object possesses due to its position.
RADIATION:
The transfer of heat by means of electromagnetic waves, which require no physical medium (e.g., water or air) for the transfer. Earth receives the Sun's heat by means of radiation.
SECOND LAW OF THERMODYNAMICS:
A law of thermodynamics which states that no engine can be constructed that simply takes heat from a source and performs an equivalent amount of work. Some of the heat will always be lost, and therefore it is impossible to build a perfectly efficient engine. This is a result of th efact that the natural flow of heat is always from a high-temperature reservoir to alow-temperature reservoir—a fact expressed in the concept of entropy. The second law is sometimes referred to as "the law of entropy."
SYSTEM:
In physics, the term "system" usually refers to any set of physical interactions isolated from the rest of the universe. Anything outside of the system, including all factors and forces irrelevant to a discussion of that system, is known as the environment.
TEMPERATURE:
The direction of internal energy flow between bodies when heat is being transferred. Temperature measures the average molecular kinetic energy in transit between those bodies.
THERMAL ENERGY:
Heat energy, a form of kinetic energy produced by the movement of atomic or molecular particles. The greater the movement of the separticles, the greater the thermal energy.
THERMODYNAMICS:
The study of the relationships between heat, work, and energy.
THIRD LAW OF THERMODYNAMICS:
A law of thermodynamics which states that at the temperature of absolute zero, entropy also approaches zero. Zero entropy would contradict the second law of thermodynamics, meaning that absolute zero is therefore impossible to reach.
WORK:
The exertion of force over a given distance to displace or move an object. Work is thus the product of force and distance exerted in the same direction.