Does Heat Energy Increase the Rest Mass of a Substance?

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Discussion Overview

The discussion centers around the relationship between heat energy and the rest mass of a substance, exploring theoretical implications and interpretations of mass-energy equivalence in the context of thermodynamics and relativistic physics.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants suggest that heating a substance increases its mass due to the energy added in the form of heat, referencing E = mc².
  • Others argue that while energy may increase mass, it does not change the rest mass or invariant mass of the substance.
  • A participant points out that rest mass is defined as the mass measured by an object moving at the same velocity, which complicates the measurement when molecules have different velocities.
  • Another participant asserts that adding heat to a body does increase its rest mass, providing an example involving two particles moving in opposite directions.
  • One participant clarifies their earlier confusion by distinguishing between adding energy as heat versus adding energy in the form of velocity to the entire object.

Areas of Agreement / Disagreement

Participants express differing views on whether heating a substance affects its rest mass, with some asserting it does and others maintaining that it does not. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

There are unresolved assumptions regarding the definitions of mass and energy in different contexts, as well as the implications of relativistic effects on mass measurements.

nhmllr
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I've heard that if you heat up a substance it masses very slightly more, because of E = mc2, and the ebergy added is in the form of heat
I am just curious - could you also think of it as m = m0 / \sqrt{1 - v^2 / c^2} because heat energy is just really diffuse kinetic energy on a molecular scale, and the small sums of all of the masses added is measurable given extremely precise instruments?
 
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I would assume you are correct, but remember that having more mass doesn't change the rest mass, or invariant mass, or whatever you want to call it.
 
Drakkith said:
I would assume you are correct, but remember that having more mass doesn't change the rest mass, or invariant mass, or whatever you want to call it.

Right, but rest mass is the mass measured by an object also moving at the same velocity, which is impossible when ever molecule has a different velocity vector.
 
Drakkith said:
I would assume you are correct, but remember that having more mass doesn't change the rest mass, or invariant mass, or whatever you want to call it.

If you add heat to a body, you *do* increase its rest mass.

To take the simplest nontrivial case, suppose you have a system of two particles, each of rest mass m, moving in opposite directions at speed v. Taken as a single unit, these two particles have a rest mass of more than 2m.
 
bcrowell said:
If you add heat to a body, you *do* increase its rest mass.

To take the simplest nontrivial case, suppose you have a system of two particles, each of rest mass m, moving in opposite directions at speed v. Taken as a single unit, these two particles have a rest mass of more than 2m.

Ah ok. I was thinking of adding energy in the form of velocity to the whole object, not heat. Sorry.
 

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