# Mechanical equivalent of heat

1. Dec 11, 2007

### miss photon

we define mech equivalent of heat as the amount of work done in joules in order to provide 1 cal of energy.
4.2 J= 1 cal
is mech equiv of heat simply a conversion factor or does it have any other physical significance?

2. Dec 11, 2007

### rbj

the Joule and the Calorie are both units of measures of energy, but defined differently, so with the necessary analysis (or experiment), they can be (and are) related by a conversion factor.

3. Dec 11, 2007

### Staff: Mentor

An example: If pushing an object against friction requires 4.2J, it will generate 1 cal of heat. Thermodynamics is basically the study of converting energy between heat and mechanical.

4. Dec 12, 2007

### miss photon

that doesn't answer my question, is there any physical significance of mechanical equivalent of heat?

5. Dec 12, 2007

### Staff: Mentor

The particular value is just a conversion factor, but the fact that you can "convert" mechanical energy to thermal energy at all is extremely significant. This led the way to the modern concept of energy conservation and the idea that while it takes various forms, all "energy" is equivalent. Joule performed a classic experiment in 1843 to demonstrate the equivalence of "heat" energy and mechanical work: http://en.wikipedia.org/wiki/Mechanical_equivalent_of_heat" [Broken]

Last edited by a moderator: May 3, 2017
6. Dec 12, 2007

### alvaros

miss photon:
Yes, it have any other physical significance.
Because heat is just the mechanical energy of atoms or molecules there must be a way to derive 1 cal from 1 Joule.
In a gas there must be a simple way of doing that, if you define 1 cal in function of pressure of the gas.
In solids, I think you must apply QM.

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