# Absolute heat ?

1. Nov 17, 2004

### Victor Frankenstein

Absolute temperature

Is there such a thing as absolute temperature, where something just can't get any hotter ?

Last edited: Nov 17, 2004
2. Nov 17, 2004

### Clausius2

The threshold of classical thermodynamics temperature is $$\infty$$. As $$T\rightarrow\infty$$ the adiabatic constant $$\gamma\rightarrow 1$$ and Gas Dynamics equations start to fail.

EDIT: That has nothing to do with heat. Heat and temperature itself are not relationed, because the "heat of a body" does not exist. So that, talking about an upper limit for heat has no sense.

Last edited: Nov 17, 2004
3. Nov 17, 2004

### Victor Frankenstein

Im confused here, whats the difference bettween temperature, heat and internal energy ?

4. Nov 17, 2004

### Clausius2

Temperature and internal energy are a measure of the thermal energy of a body. This thermal energy is relationed to kinetic energy of its atoms via Kinetic Theory. Heat is the amount of energy being or been transferred between two bodies. The usual comparison between heat and temperature is made with Hydraulics. Imagine two vessels filled each other with heights H1 and H2 of water and connected by a closed pipe between them. The measure of the Temperature would be each absolute height, and the measure of the heat transferred would be compared with the volume flux produced when you open the pipe's valve. Think of it, and realize that volume flux does not depend on those absolute heights, but in their difference.

5. Nov 17, 2004

### Iraides Belandria

Clausius, Please, excuse me if I ask a different but related question. In this case, is temperature and the internal energy difference absolute or relative?. ¿ If we measure temperature and internal energy difference in a rest frame , will it be different to a measurement in a frame moving at the velocity of light?. ¿ Will the thermodynamic internal energy coincides with einstein energy at rest, with e=mc2?.

6. Nov 18, 2004

### Clausius2

Well, that's a question you may as well ask to a physicist. An engineer will say the absolute level of energy is meaningless and unuseful. For instance, taking into account the relativistic energy as you said in a thermodynamic calculation is non sense, because that energy and all the other imaginable energies remains constant or very approximately constant in the process, and thermodynamic or usual energy calculations are made based on differences of energies. As far as I know internal (thermal) energy has nothing to do with einstein energy at rest.

About the reference frame, the static temperature remains constant under a change of reference frame. If you have studied gas dynamics, you must know there are two different ways of talking about temperature: static and stagnation temperature. The first is calculated via equation of state PV=nRT. In that equation, no reference frame is specified, so it is always yield no matter which frame you choose. The second is calculated via Bernoulli's generalized equation. But there in the v^2/2 term one can write the flow velocity or some galilean translation you want.

To sum up, you only have temperatures depending on reference frame when you talk about stagnation temperatures. The usual choice is not doing any change of reference frame (it would be very fool to do that because fluid flow problems are enough difficult yet), but in fact it admit such a change.
This kind of change is sometimes employed at Turbomachinery analysis, where rotating frame vs inertial frame plays an important role into the formulation.

On the contrary, static temperature is the same no matter which reference frame are you viewing from, because it comes from the equation of state.