Mechanical Equivalent of Heat

mechanical equivalent of heat

[mi′kan·ə·kəl i′kwiv·ə·lənt əv ′hēt] (thermodynamics) The amount of mechanical energy equivalent to a unit of heat.

Mechanical Equivalent of Heat

the amount of work that is equivalent to a unit quantity of heat in a heat-transfer process [in calories (cal) or kilocalories (kcal)]. The concept arose because, historically, mechanical work and amount of heat were measured in different units. After the equivalence between mechanical work and heat had been established by J. R. von Mayer in 1842, measurements were made with great care by J. P. Joule from 1843 to 1878, the Swedish scientist E. Edlund in 1865, the American physicist H. A. Rowland in 1879, and others. The results of the measurements indicated that 1 kcal = 426.9 kilogram-force-meters (kgf-m). In the International System of Units the concept of the mechanical equivalent of heat is not needed because the same unit—the joule (J)—is used for the measurement of both work and the quantity of transmitted heat: 1 J = 0.239 cal = 0.102 kgf-m.

Table 1. Comparative characteristics of main types of measuring heads
Type	Size of scale division (μ)	Range measurement (μ)	Error
Mechanical comparator (microcator) ........	10, 2, 0.5, 0.2, 0.1 (experimental models: 0.05, 0.02)	± (300, 150, 60, 30, 15, 6, 4)	± 0.5% of a scale division
Micator ........	0.2,0.5,1,2	±(100,50,25,10)	± (0 3-20.0 μ)
Minicator ........	1,2,0.5,	±(80,40,20)	not more than a scale division

mechanical equivalent of heat

The number of units of mechanical energy equal to one unit of heat, e.g., 778.2 ft-lb (107.6 kg-m) equals 1 Btu; 4.187 joules equals 1 calorie.