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6

A cubic metre void of anything cannot be described with a temperature. Spacetime itself does not have the property of temperature, so it would be incorrect to say such a void is at absolute zero. However, it is not necessary that any volume not at absolute zero has mass. The property of temperature could be held by photons or other massless particles. For ...


6

The notion of temperature is all about how the equilibrium an otherwise isolated system shifts when the system's internal energy changes. So you do not need to worry about whether this internal energy is kinetic, potential, whatever. Actually the temperature is not quite the ensemble average kinetic energy. Your statement is true for an ideal gas and also ...


3

Object don't posses heat. They posses internal energy. Heat, like work, is a transfer of energy and is a property of a process or interaction not of an object.


3

You asked for intuitive sense and I'll try to provide it. The formula is: $$\Delta S = \frac{\Delta Q}{T}$$ So, you can have $\Delta S_1=\frac{\Delta Q}{T_{lower}}$ and $\Delta S_2=\frac{\Delta Q}{T_{higher}}$ Assume the $\Delta Q$ is the same in each case. The denominator controls the "largeness" of the $\Delta S$. Therefore, $\Delta S_1 > \Delta ...


2

The expansion of the universe is related to its cooling. Temperature is defined as the inverse of the partial derivative of entropy with respect to energy: $$ \frac{1}{T}=\frac{\partial S}{\partial E} $$ The derivative is taken at constant volume. This is the definition of temperature. This definition only makes sense for macroscopic bodies. I.e., ...


2

The energy of any infalling mass is absorbed by the black hole. Classically, the temperature of a black hole is absolute zero, since it is a perfect absorber. If you include quantum mechanical effects, as Stephen Hawking did, you can show that black hole horizons will emit radiation in such a way that is consistent with the horizon being a hot body with ...


2

Your breath is the same temperature either way. The difference is how much ambient air is brought along with the breath by the time it reaches the object. Emitting a thin and fast stream of air will cause a lot of other air to follow along with it. When you are blowing on the soup to cool it, what you're really doing is using your breath to move a lot of ...


2

This is a difficult question for many reasons. One reason is likely because most of the introductory thermodynamics textbook problems that we are familiar with from childhood do not involve gravity. To illustrate this difficulty with gravity consider, for example, this snippet from an article in the New York Times Review of Books by physicist/mathematician ...


2

Heat is a type of energy transfer from one system to another, rather than an internal energy of any given system ('thermal energy' might be a good term for what you're thinking of). In An Introduction to Thermal Physics by Daniel Schroeder, p. 18 says: Heat is defined as any spontaneous flow of energy from one object to another caused by a difference in ...


2

I have contributed this issue with this arXiv:1411.2425 and previous works. I stress that Gibbs entropy is not "defined" but rather "constructed". It is constructed on the expression of thermodynamic forces in the microcanonical ensemble, and is constructed in such a way that it reproduces them always and exactly. The construction is actually unique. ...


2

Heat added to a system at a lower temperature causes higher entropy increase than heat added to the same system at a higher temperature. How does this make intuitive sense? The formula defines entropy change. Since it defines new word not conceived before and thus devoid of sense, it is hard to imagine as having "intuitive sense". If your question ...


1

I find that the question here relates directly to the definition of temperature, and I'll give a short version of it. For simplicity let us consider a system generated by two sub-systems, A and B, in thermal contact (meaning they only exchange energy in the form of heat). Let me state that, for $A$ and $B$ in thermal equilibrium, the entropy $S_{A}$ and ...


1

Temperature is a quantity that determines how heat flows into and out of a system of particles when it is placed in contact with other systems. By this definition, measuring the temperature of a system with no mass inside is nonsensical; it's not absolute zero, it's undefined. Temperature can equivalently be defined as being proportional to the average ...


1

As mentioned in the comment above, temperature is defined to be a measure of the average kinetic energy of the particles in a system. So with that definition, the answers to your questions should fall out naturally: If there is no mass in a volume, you could say the temperature is absolute zero. I would say it isn't defined because you cannot take the ...


1

Intuitively, For a gas,if you apply heat to the container of gas the kinetic energies of the molecules or atoms increase,means heat added is used in increasing the kinetic energies of the molecules. As we know ,temperature of a gas depends on how fast the molecules of gas moving or vibrating ,so on heating temperature of the gas increases. Now these ...


1

It's an example of adiabatic expansion. If you have a container full of gas and you expand the container, the gas cools. Entropy is preserved. Adiabatic processes preserve entropy. Any decrease in entropy due to lowered energy, and correspondingly fewer possible velocities for the particles, is offset by an increase in entropy due to the expanding volume, ...


1

Let me show you that there is no contradiction by pointing out e.g. that for ordinary expansion periods (that is away from first order phase transitions, decouplings...) the total entropy is actually constant in time while the universe is getting bigger and cooler. Or, going back in time, the universe is getting hotter while S is kept constant. How is this ...


1

Consider each molecule. As you say, masses $m$ are constant but volumes usually grow with higher temperature. That hot air molecules will float up is not do to any changes in mass or so - but to changes in density $\rho$: $$\rho=\frac{m}{V}$$ The fluid of highest density will seek the bottom, and this will be the colder air molecules: ...



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