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calorie,abbr. cal, unit of heatheat,
nonmechanical energy in transit, associated with differences in temperature between a system and its surroundings or between parts of the same system. Measures of Heat
..... Click the link for more information. energy in the metric system. The measurement of heat is called calorimetrycalorimetry
, measurement of heat and the determination of heat capacity. Heat is evolved in exothermic processes and absorbed in endothermic processes; such processes include chemical reactions, transitions between the states of matter, and the mixing of two substances to form
..... Click the link for more information. . The calorie, or gram calorie, is the quantity of heat required to raise the temperature of 1 gram of pure water 1°C;. The kilocalorie, or kilogram calorie, is the quantity of heat required to raise the temperature of 1 kg of pure water 1°C;; it is equal to 1,000 cal. The kilocalorie is used in dietetics for stating the heat content of a food, i.e., the amount of heat energy that the food can yield as it passes through the body; in this context, the kilocalorie is usually called simply the calorie. The amount of heat energy needed to effect a 1°C; temperature increase in 1 gram of water varies with temperature (see heat capacityheat capacity
or thermal capacity,
ratio of the change in heat energy of a unit mass of a substance to the change in temperature of the substance; like its melting point or boiling point, the heat capacity is a characteristic of a substance.
..... Click the link for more information. ); thus the temperature range over which the heating takes place must be stated to define the calorie precisely. The 15° calorie, or normal calorie, is widely used in chemistry and physics; it is measured by heating a 1-gram water sample from 14.5°C; to 15.5°C; at 1 atmosphere pressure. The 4° calorie, also called the small calorie or therm, is measured from 3.5°C; to 4.5°C; (water is most dense at 3.98°C;); the large calorie, or Calorie, is equivalent to 1,000 small calories. The average value of the calorie in the range 0°C; to 100°C; is called the mean calorie; it is 1-100 of the energy needed to heat 1 gram of water from its melting point to its boiling point. The calorie may also be defined by expressing its value in some other energy units. The 15° calorie is equivalent to 4.185 joulesjoule
, abbr. J, unit of work or energy in the mks system of units, which is based on the metric system; it is the work done or energy expended by a force of 1 newton acting through a distance of 1 meter. The joule is named for James P. Joule.
..... Click the link for more information. (J), 1.162×10−6 kilowatt-hours, 3.968×10−3 British thermal units, and 3.087 foot-pounds; the 4° calorie equals 4.204 J; and the mean calorie equals 4.190 J. Two other calories sometimes used are the International Steam Table calorie, equal to 4.187 J, and the thermochemical calorie, equal to 4.184 J. When the calorie is used for precision measurement of heat energy, the particular calorie being used must be specified.
a unit of heat that is not part of a system of units. Designation, cal. In addition to the calorie, the kilocalorie (also known as the large calorie) is widely used; 1 kcal = 1,000 cal.
Originally, the calorie was defined as the quantity of heat necessary to raise the temperature of 1 g of water by 1°C. Neither the temperature interval within which the heating was performed nor its conditions had been defined prior to the late 19th century. Various calories have therefore been used: the 0°, 15°, 20°, and 25° calories as well as the average calorie and the thermochemical calorie. The 20° kilocalorie was used in the USSR from 1934 to 1957. This kilocalorie was equal to the quantity of heat (with an accuracy of up to 0.02 percent) required to heat 1 kg of water from 19.5° to 20.5°C.
The First International Steam Table Conference (London, 1929) introduced the international calorie, defined as 1/861.1 of the international kilowatt-hour (kW-hr). The InternationalSteam Table Conferences in 1954 and 1956 accepted the decisionon transition from the calorie to a new unit, the absolute joule(J), which subsequently was included in the International Sys-tem of Units. The following relationship was established betweenthe calorie and the joule: 1 cal = 4.1868 J (exactly). The 20°calorie is equal to 4.181 J. The calorie used widely in thermo-chemistry is equal to 4.1840 J.