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Key People:Antoine LavoisierWilliam Thomson, Baron KelvinHenry CavendishSir Benjamin Thompson, count von RumfordJames Prescott Joule...(Show more)Related Topics:latent heatenthalpythermal conductionheat capacitycaloric theory...(Show more)
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heat, power that is transferred from one body to another as the result of a distinction in temperature. If two bodies at various temperatures are carried together, energy is transferred—i.e., warm flows—from the hotter human body to the colder. The impact of this transfer of power usually, however not always, is rise in the temperature that the colder body and a decrease in the temperature that the hotter body. A substance may absorb heat without rise in temperature by changing from one physical state (or phase) to another, together from a solid come a fluid (melting), indigenous a solid come a vapour (sublimation), from a liquid to a vapour (boiling), or native one solid form to one more (usually dubbed a crystalline transition). The important distinction between heat and temperature (heat being a type of energy and also temperature a measure of the lot of that energy existing in a body) was clarified throughout the 18th and also 19th centuries.

Heat together a form of energy

Because every one of the many forms that energy, consisting of heat, can be converted into work, quantities of power are to express in devices of work, such as joules, foot-pounds, kilowatt-hours, or calories. Specific relationships exist in between the amounts of heat included to or gotten rid of from a body and also the magnitude of the effects on the state that the body. The two units of warmth most generally used are the calorie and also the British thermal unit (BTU). The calorie (or gram-calorie) is the quantity of energy required come raise the temperature that one gram that water from 14.5 come 15.5 °C; the BTU is the lot of power required come raise the temperature that one lb of water from 63 to 64 °F. One BTU is approximately 252 calories. Both meanings specify that the temperature transforms are to be measured in ~ a consistent pressure of one atmosphere, since the amounts of energy involved depend in component on pressure. The calorie provided in measure up the energy content of foodstuffs is the huge calorie, or kilogram-calorie, same to 1,000 gram-calories.


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In general, the amount of energy required to raise a unit mass of a substance v a mentioned temperature expression is referred to as the heat capacity, or the particular heat, of the substance. The quantity of energy necessary come raise the temperature that a human body one level varies depending on the restraints imposed. If heat is included to a gas limit at continuous volume, the lot of heat needed to reason a one-degree temperature increase is much less than if the warm is added to the exact same gas totally free to broaden (as in a cylinder fitted with a movable piston) and so execute work. In the very first case, every the power goes right into raising the temperature the the gas, however in the 2nd case, the energy not only contributes come the temperature boost of the gas but also provides the energy necessary because that the work-related done by the gas ~ above the piston. Consequently, the specific heat the a substance relies on this conditions. The most typically determined particular heats room the certain heat at constant volume and the details heat at consistent pressure. The warmth capacities of countless solid elements were presented to be closely related to their atomic weights by the French researchers Pierre-Louis Dulong and also Alexis-Thérèse Petit in 1819. The so-called regulation of Dulong and Petit was beneficial in identify the atom weights of particular metallic elements, but there are plenty of exceptions to it; the deviations to be later uncovered to be explainable on the basis of quantum mechanics.

It is incorrect to speak the the warm in a body, since heat is limited to energy being transferred. Energy stored in a human body is not warmth (nor is it work, as occupational is additionally energy in transit). That is customary, however, come speak that sensible and also latent heat. The latent heat, additionally called the warmth of vaporization, is the amount of energy necessary to adjust a fluid to a vapour at continuous temperature and also pressure. The power required come melt a solid to a liquid is referred to as the warmth of fusion, and also the heat of sublimation is the power necessary to readjust a solid directly to a vapour, these changes likewise taking ar under conditions of continuous temperature and pressure.

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Air is a mixture of gases and water vapour, and it is possible for the water present in the wait to change phase; i.e., that may become liquid (rain) or heavy (snow). To distinguish between the energy associated with the phase change (the latent heat) and also the energy required for a temperature change, the principle of sensible heat was introduced. In a mixture of water vapour and air, the sensible warmth is the energy necessary to produce a particular temperature change excluding any kind of energy required for a step change.