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Definition: calorie from Dictionary of Energy

Measurement. a unit of energy, defined as the amount of heat transfer required to raise the temperature of one gram of pure water by one degree Celsius (from 14.5°C- 15.5°C) at standard atmospheric pressure (sea level); equivalent to 4.184 J. Used as a description of the energy content of a given food. Also called a small calorie in contrast with a kilocalorie or large calorie (1000 small calories).


Summary Article: calorie from The Columbia Encyclopedia

abbr. cal, unit of heat energy in the metric system. The measurement of heat is called calorimetry. The calorie, or gram calorie, is the quantity of heat required to raise the temperature of 1 gram of pure water 1degrees Celsius. The kilocalorie, or kilogram calorie, is the quantity of heat required to raise the temperature of 1 kg of pure water 1degrees Celsius; 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 1degrees Celsius temperature increase in 1 gram of water varies with temperature (see heat capacity); 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 14.5degrees Celsius to 15.5degrees Celsius at 1 atmosphere pressure. The 4° calorie, also called the small calorie or therm, is measured from 3.5degrees Celsius to 4.5degrees Celsius (water is most dense at 3.98degrees Celsius); the large calorie, or Calorie, is equivalent to 1,000 small calories. The average value of the calorie in the range 0degrees Celsius to 100degrees Celsius 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 joules (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.

The Columbia Encyclopedia, © Columbia University Press 2017

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