![]() The unit of heat energy is the calorie which is defined as that amount of heat whose absorption by 1 gram (gm) of water at constant atmospheric pressure is accompanied by a temperature rise from 14.5 to 15.5 ° C. It is incorrect to refer to ‘heat in a body’ because heat is not a substance. ![]() An early 19th century theory incorrectly regarded heat as a liquid called ‘caloric’. Heat is defined as that energy which is transferred between a system and its surroundings solely by virtue of a temperature difference. A result of mechanical work on, or by, a system can be a change in kinetic energy, a change in potential energy of the system as in the case of compressing a spring, or dissipation into heat as in the case of boring out the centre of a cannon. Work depends on the particular process by which a system is taken from a reference state to a second state. It is meaningless to talk of ‘work in a system’ or ‘work of a system’. Work is said to be done on a system if that system experiences a displacement as the result of a force parallel to and in the same direction as that force. However, if consumption is less than recommended daily requirements, the body will supplement its energy sources by drawing upon stores of fat and the person will lose weight.In thermodynamics, a sub-field of physics, the words ‘energy’ and ‘work’ have precise definitions with meanings which differ from colloquial use of these words.Įnergy is defined as 'the ability to do work on other bodies’ or as ‘stored work’. If the average adult consumes more calories than the daily requirement, he or she will gain weight. ![]() These tabulations serve only as guides they cannot, of course, embrace all individual variations.įrom its daily intake of energy foods, the body uses only the amount it needs for energy purposes. Nutrition experts have computed daily calorie requirements in terms of age and other factors. ![]() Factors such as weight, age, activity, and metabolic rate determine a person's daily calorie requirement. The amount of energy required for these chemical processes varies. Digestive processes reduce food to usable “fuel,” which the body “burns” in the complex chemical reactions that sustain life. ![]() Every bodily process, including the building up of cells, motion of the muscles, and the maintenance of body temperature, requires energy, which the body derives from the food it consumes. In referring to the energy content of foods it is customary to use the “large calorie,” which is equal to 1 kilocalorie (kcal). The calorie used in chemistry and biochemistry is equal to 4.184 joules. Any of several units of heat defined as the amount of heat required to raise the temperature of 1 kilogram of water by 1 degree Celsius (1☌) at a specified temperature. ![]()
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