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Key People:Antoine LavoisierWilliam Thomson, Baron KelvinHenry CavendishSir Benjamin Thompson, counting von RumfordJames Prescott Joule...(Show more)Related Topics:latent heatenthalpythermal conductionheat capacitycaloric theory...(Show more)
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heat, energy that is transferred from one body to another as the result of a difference in temperature. If 2 bodies at different temperatures are brought together, energy is transferred—i.e., heat flows—from the hotter body to the colder. The effect of this transfer of energy usually, however not always, is boost in the temperature of the chillier body and also a diminish in the temperature of the hotter body. A substance might absorb warmth without rise in temperature by transforming from one physical state (or phase) to another, as from a solid come a liquid (melting), native a solid to a vapour (sublimation), native a liquid to a vapour (boiling), or from one solid kind to another (usually referred to as a crystalline transition). The important difference between heat and temperature (heat gift a kind of energy and temperature a measure up of the amount of the energy present in a body) was clarified throughout the 18th and 19th centuries.

Heat together a type of energy

Because all of the many forms the energy, consisting of heat, have the right to be converted right into work, quantities of power are expressed in units of work, such as joules, foot-pounds, kilowatt-hours, or calories. Precise relationships exist in between the quantities of heat included to or removed from a body and also the size of the results on the state that the body. The 2 units of heat most generally used space the calorie and the British heat unit (BTU). The calorie (or gram-calorie) is the quantity of power required come raise the temperature that one gram that water from 14.5 to 15.5 °C; the BTU is the lot of energy required to raise the temperature that one pound of water from 63 to 64 °F. One BTU is approximately 252 calories. Both definitions specify that the temperature changes are to be measured at a consistent pressure of one atmosphere, because the amounts of energy connected depend in part on pressure. The calorie provided in measuring the energy content of foods is the large calorie, or kilogram-calorie, same to 1,000 gram-calories.


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In general, the amount of energy required come raise a unit mass of a substance through a specified temperature expression is referred to as the warm capacity, or the specific heat, of that substance. The amount of energy necessary come raise the temperature that a body one degree varies relying on the restraints imposed. If warm is added to a gas limit at consistent volume, the quantity of warmth needed to reason a one-degree temperature rise is much less than if the heat is added to the exact same gas cost-free to broaden (as in a cylinder fitted with a movable piston) and also so perform work. In the first case, every the energy goes right into raising the temperature the the gas, yet in the 2nd case, the power not only contributes come the temperature rise of the gas but additionally provides the power necessary because that the work done through the gas ~ above the piston. Consequently, the specific heat of a substance depends on this conditions. The most commonly determined certain heats room the certain heat at continuous volume and the particular heat at continuous pressure. The warm capacities of numerous solid aspects were shown to be closely related to their atomic weights by the French scientists Pierre-Louis Dulong and also Alexis-Thérèse Petit in 1819. The so-called legislation of Dulong and also Petit was beneficial in identify the atomic weights of particular metallic elements, however there are many exceptions come it; the deviations to be later found to it is in explainable ~ above the communication of quantum mechanics.

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

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