What is "mechanical equivalent of heat"

Equivalent \E*quiv"a*lent\ ([-e]*kw[i^]v"[.a]*lent), n.

1. Something equivalent; that which is equal in value, worth, weight, or force; as, to offer an equivalent for damage done.

   He owned that, if the Test Act were repealed, the Protestants were entitled to some equivalent. . . . During some weeks the word equivalent, then lately imported from France, was in the mouths of all the coffeehouse orators.
   --Macaulay.

2. (Chem.) That comparative quantity by weight of an element which possesses the same chemical value as other elements, as determined by actual experiment and reference to the same standard. Specifically: (a) The comparative proportions by which one element replaces another in any particular compound; thus, as zinc replaces hydrogen in hydrochloric acid, their equivalents are 32.5 and

   1. (b) The combining proportion by weight of a substance, or the number expressing this proportion, in any particular compound; as, the equivalents of hydrogen and oxygen in water are respectively 1 and 8, and in hydric dioxide 1 and 16.

      Note: This term was adopted by Wollaston to avoid using the conjectural expression atomic weight, with which, however, for a time it was practically synonymous. The attempt to limit the term to the meaning of a universally comparative combining weight failed, because of the possibility of several compounds of the substances by reason of the variation in combining power which most elements exhibit. The equivalent was really identical with, or a multiple of submultiple of, the atomic weight.

3. (Chem.) A combining unit, whether an atom, a radical, or a molecule; as, in acid salt two or more equivalents of acid unite with one or more equivalents of base.

   Mechanical equivalent of heat (Physics), originally defined as the number of units of work which the unit of heat can perform, equivalent to the mechanical energy which must be expended to raise the temperature of a pound of water one degree Fahrenheit; later this value was defined as one British thermal unit (B.t.u). Its value was found by Joule to be 772 foot pounds; later measurements give the value as 777.65 foot-pounds, equivalent to 107.5 kg-meters. This value was originally called Joule's equivalent, but the modern Joule is defined differently, being 10^ 7 ergs. The B.t.u. is now given as 1,05

4. 35 absolute Joules, and therefore 1 calorie (the amount of heat needed to raise one gram of water one degree centigrade) is equivalent to 4.186 Joules.

   Note: The original definition of the Mechanical equivalent of heat in the 1913 Webster was as below. The difference between foot pounds and kilogram-meters ("on the centigrade scale") is puzzling as it should be a factor of 7.23, and the figure given for kilogram-meters may be a mistaken misinterpretation of the report. -- PJC: The number of units of work which the unit of heat can perform; the mechanical energy which must be expended to raise the temperature of a unit weight of water from 0[deg] C. to 1[deg] C., or from 32[deg] F. to 33[deg] F. The term was introduced by Dr. Mayer of Heilbronn. Its value was found by Joule to be 1390 foot pounds upon the Centigrade, or 772 foot pounds upon the Fahrenheit, thermometric scale, whence it is often called Joule's equivalent, and represented by the symbol J. This is equal to 424 kilogram meters (Centigrade scale). A more recent determination by Professor Rowland gives the value 426.9 kilogram meters, for the latitude of Baltimore.

Heat \Heat\ (h[=e]t), n. [OE. hete, h[ae]te, AS. h[=ae]tu, h[=ae]to, fr. h[=a]t hot; akin to OHG. heizi heat, Dan. hede, Sw. hetta. See Hot.]

1. A force in nature which is recognized in various effects, but especially in the phenomena of fusion and evaporation, and which, as manifested in fire, the sun's rays, mechanical action, chemical combination, etc., becomes directly known to us through the sense of feeling. In its nature heat is a mode of motion, being in general a form of molecular disturbance or vibration. It was formerly supposed to be a subtile, imponderable fluid, to which was given the name caloric.

   Note: As affecting the human body, heat produces different sensations, which are called by different names, as heat or sensible heat, warmth, cold, etc., according to its degree or amount relatively to the normal temperature of the body.

2. The sensation caused by the force or influence of heat when excessive, or above that which is normal to the human body; the bodily feeling experienced on exposure to fire, the sun's rays, etc.; the reverse of cold.

3. High temperature, as distinguished from low temperature, or cold; as, the heat of summer and the cold of winter; heat of the skin or body in fever, etc.

   Else how had the world . . . Avoided pinching cold and scorching heat!
   --Milton.

4. Indication of high temperature; appearance, condition, or color of a body, as indicating its temperature; redness; high color; flush; degree of temperature to which something is heated, as indicated by appearance, condition, or otherwise.

   It has raised . . . heats in their faces.
   --Addison.

   The heats smiths take of their iron are a blood-red heat, a white-flame heat, and a sparkling or welding heat.
   --Moxon.

5. A single complete operation of heating, as at a forge or in a furnace; as, to make a horseshoe in a certain number of heats.

6. A violent action unintermitted; a single effort; a single course in a race that consists of two or more courses; as, he won two heats out of three.

   Many causes . . . for refreshment betwixt the heats.
   --Dryden.

   [He] struck off at one heat the matchless tale of ``Tam o' Shanter.''
   --J. C. Shairp.

7. Utmost violence; rage; vehemence; as, the heat of battle or party. ``The heat of their division.''
   --Shak.

8. Agitation of mind; inflammation or excitement; exasperation. ``The heat and hurry of his rage.''
   --South.

9. Animation, as in discourse; ardor; fervency; as, in the heat of argument.

   With all the strength and heat of eloquence.
   --Addison.

10. (Zo["o]l.) Sexual excitement in animals; readiness for sexual activity; estrus or rut.

11. Fermentation.

12. Strong psychological pressure, as in a police investigation; as, when they turned up the heat, he took it on the lam. [slang]

    Animal heat, Blood heat, Capacity for heat, etc. See under Animal, Blood, etc.

    Atomic heat (Chem.), the product obtained by multiplying the atomic weight of any element by its specific heat. The atomic heat of all solid elements is nearly a constant, the mean value being 6.4.

    Dynamical theory of heat, that theory of heat which assumes it to be, not a peculiar kind of matter, but a peculiar motion of the ultimate particles of matter.

    Heat engine, any apparatus by which a heated substance, as a heated fluid, is made to perform work by giving motion to mechanism, as a hot-air engine, or a steam engine.

    Heat producers. (Physiol.) See under Food.

    Heat rays, a term formerly applied to the rays near the red end of the spectrum, whether within or beyond the visible spectrum.

    Heat weight (Mech.), the product of any quantity of heat by the mechanical equivalent of heat divided by the absolute temperature; -- called also thermodynamic function, and entropy.

    Mechanical equivalent of heat. See under Equivalent.

    Specific heat of a substance (at any temperature), the number of units of heat required to raise the temperature of a unit mass of the substance at that temperature one degree.

    Unit of heat, the quantity of heat required to raise, by one degree, the temperature of a unit mass of water, initially at a certain standard temperature. The temperature usually employed is that of 0[deg] Centigrade, or 32[deg] Fahrenheit.

In the history of science, the mechanical equivalent of heat states that motion and heat are mutually interchangeable and that in every case, a given amount of work would generate the same amount of heat, provided the work done is totally converted to heat energy. The mechanical equivalent of heat was a concept that had an important part in the development and acceptance of the conservation of energy and the establishment of the science of thermodynamics in the 19th century.