The Significance of the Mechanical Equivalent of Heat

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Discussion Overview

The discussion centers on the mechanical equivalent of heat, specifically the relationship between mechanical work and thermal energy, as well as its significance beyond being a mere conversion factor. Participants explore its implications in thermodynamics and energy conservation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants define the mechanical equivalent of heat as the amount of work done in joules to provide 1 calorie of energy, noting the conversion factor of 4.2 J = 1 cal.
  • Others argue that while the Joule and the Calorie are related as units of energy, their definitions differ, and this relationship can be established through analysis or experimentation.
  • One participant provides an example illustrating that pushing an object against friction requires 4.2 J to generate 1 cal of heat, suggesting that thermodynamics involves converting energy between heat and mechanical forms.
  • Another participant emphasizes that the ability to convert mechanical energy to thermal energy is significant, as it contributed to the modern understanding of energy conservation and equivalence of energy forms.
  • A later reply suggests that the mechanical equivalent of heat has deeper physical significance, proposing that heat can be viewed as the mechanical energy of atoms or molecules, and hints at deriving 1 cal from 1 Joule in specific contexts, such as gases or solids involving quantum mechanics.

Areas of Agreement / Disagreement

Participants express differing views on whether the mechanical equivalent of heat is merely a conversion factor or if it holds additional physical significance. The discussion remains unresolved regarding the deeper implications of this concept.

Contextual Notes

Participants mention the historical context of Joule's experiments and the relationship between mechanical and thermal energy, but do not fully resolve the implications of these ideas or the definitions involved.

miss photon
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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?
 
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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.
 
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.
 
russ_watters said:
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.

that doesn't answer my question, is there any physical significance of mechanical equivalent of heat?
 
miss photon said:
that doesn't answer my question, is there any physical significance of mechanical equivalent of heat?
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"
 
Last edited by a moderator:
miss photon:
is mech equiv of heat simply a conversion factor or does it have any other physical significance?

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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