The temperature at which all molecular motion virtually ceases.
The reflective power of a surface or body or, more specifically, the proportion of incoming radiation that the surface or body reflects.
In general, an atmosphere is a blanket of gases surrounding a planet. Unless otherwise identified, however, the term refers to the atmosphere of Earth, which consists of nitrogen (78%), oxygen (21%), argon (0.93%), and other substances that include water vapor, carbon dioxide, ozone, and noble gases such as neon, which together comprise 0.07%.
Energy derived from biological sources that are used directly as fuel (as opposed to food, which becomes fuel).
Materials that are burned or processed to produce bioenergy.
A combination of all living things on Earth—plants, mammals, birds, reptiles, amphibians, aquatic life, insects, viruses, single-cell organisms, and so on—as well as all formerly living things that have not yet decomposed.
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 g of water to change its temperature by 1°C. The dietary calorie with which most people are familiar is the same as the kilocalorie, or 1,000 calories.
A law of physics that holds that within a system isolated from all 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.
A form of energy with electric and magnetic components, which travels in waves.
The complete range of electromagnetic waves on a continuous distribution from a very low range of frequencies and energylevels, with a correspondingly long wavelength, to a very high range of frequencies and energy levels, with a correspondingly short wavelength. Included on the electromagnetic spectrum are long-wave and short-wave radio; microwaves; infrared, visible, and ultraviolet light; x rays; and gamma rays.
The ability of an object (or in some cases a non object, such as a magnetic force field) to accomplish work.
The total amount of energy available to a system or, More specifically, the difference between the energy flowing into the system and the energy lost by it.
The tendency of natural systems toward breakdown and, specifically, the tendency for the energy in a system to be dissipated. Entropy is related closely to the second law of thermodynamics.
In discussing systems, the term environment refers to the surroundings—everything external to and separate from the system.
A law of physics stating that 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.
Nonrenewable forms of bioenergy, including petroleum, coal, peat, natural gas, and other organic compounds usable as fuel.
The number of waves, measured in Hertz, passing through a given point during the interval of one second. The higher the frequency, the shorter the wavelength.
Heat, or thermal, energy from Earth's interior.
Warming of the lower atmosphere and surface of Earth. This occurs because of the absorption of long-wave length radiation from the planet's surface by certain radiatively activegases, such as carbon dioxide and watervapor, in the atmosphere. These gases are heated and ultimately re-radiate energy at an even longer wavelength to space.
Internal thermal energy that flows from one body of matter to another.
A unit for measuring frequency, equal to one cycle per second. High frequencies are expressed in terms of kilohertz (kHz; 10 3 or 1,000 cycles per second), megahertz (MHz; 10 6 or one million cycles per second), and gigahertz (GHz; 10 9 or one billion cycles per second.)
The entirety of Earth's water, excluding water vapor in the atmosphere but including all oceans, lakes, streams, groundwater, snow, and ice.
The SI measure of work. One joule (J) is equal to the work required to accelerate 1 kg of mass by 1 m per second squared (1 m/s 2 ) over a distance of 1 m. Owing to the small size of the joule, however, it often is replaced by the kilowatt-hour, equal to 3.6 million (3.6 × 10 6 ) J.
Established by William Thompson, Lord Kelvin (1824-1907), the Kelvin scale measures temperature in relation to absolute zero, or 0K.(Note that units in the Kelvin system, known as kelvins, do not include the word or symbol for "degree.") The Kelvin scale, which is the system usually favored by scientists, is related directly to the Celsius scale; hence, Celsius temperatures can be converted to kelvins by adding 273.15.
The energy that an object possesses by virtue of its motion.
A scientific principle that is shown always to be the case and for which no exceptions are deemed possible.
The energy an object possesses by virtue of its mass. Sometimes called rest energy.
A nuclear reaction that involves the splitting of an atomic nucleus.
A nuclear reaction that involves the joining of atomicnuclei.
The center of an atom, a region where protons and neutrons are located and around which electrons spin.
The biological conversion of light energy (that is, electromagnetic energy) to chemical energy in plants.
The energy that an object possesses by virtue of its position or its ability to perform work.
The rate at which work is accomplished over time, a figure rendered mathematically as work divided by time. The SI unit of power is the watt, while the British unit is the foot-pound per second.
The transfer of energy by means of electromagnetic waves, which require no physical medium (for example, water or air) for the transfer. Earth receives the Sun's energy via the electromagnetic spectrum by means of radiation.
A term describing a phenomenon whereby certain materials are subject to a form of decay brought about by the emission of high-energy particles or radiation. Forms of particles or energy include alpha particles (positively charged helium nuclei), beta particles (either electrons or subatomic particles called positrons), or gamma rays, which occupy the highest energy level in the electromagnetic spectrum.
A law of physics stating that spontaneous or unaided transfers of energy are irreversible and impossible without an increase of entropy in the universe. It is therefore impossible, without the additional input of energy, to transfer heat from a colder to a hotter body or to convert heat into an equal amount of work.
An abbreviation of the French term Système International d'Unités, or International System of Units. Based on the metricsystem, SI is the system of measurement units in use by scientists worldwide.
Any set of interactions that can be set apart mentally from the rest of the universe for the purposes of study, observation, and measurement.
The direction of internal energy flow between two systems when heat is being transferred. Temperature measures the average molecular kinetic energy in transit between those systems.
See watt.
Heat energy, a form of kinetic energy produced by the motion of atomic or molecular particles in relation to one another. The greater the relative motion of these particles, the greater the thermal energy.
The metric unit of power, equal to 1 J per second. Because this is such a small unit, scientists and engineers typically speak in terms of kilowatts, or units of 1,000W. Very large figures, such as those relating to Earth's energy budget, usually are given in terawatts, or 10 12 (one trillion) W.
The distance between a crest and the adjacent crest or the trough and an adjacent trough of a wave. Wavelength is related inversely to frequency, meaning that the shorter the wavelength, the higher the frequency.
The exertion of force over a given distance. In the metric, or SI, system, work is measured by the joule (J) and in the British system by the foot-pound (ft-lb).
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