Covers the study of (mostly homogeneous) macroscopic systems from a heat/energy/entropy point of view. Maybe combine with [tag:statistical-mechanics].

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Reading differential forms

When, usually in text of physics or concerning thermodynamical aspects of chemistry, I find notations such as$$\mathrm{d}f=g\,\mathrm{d}t$$ I always interpretate it as $\frac{\mathrm{d}f(t)}{\mathrm{d}...
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Why is the second law of thermodynamics indisputable? [duplicate]

Why is the second law of thermodynamics undisputable? On his website Professor Hawking says the following: The cosmologist, Sir Arthur Eddington, once said, 'Don't worry if your theory doesn't ...
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Crash course in classical thermodynamics

I've been working on some projects lately where it would be very handy to know more about thermodynamics than I do, but sadly I never had a chance to take a proper thermodynamics course in college. ...
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Do photons lose energy while travelling through space? Or why are planets closer to the sun warmer?

My train of thought was the following: The Earth orbiting the Sun is at times 5 million kilometers closer to it than others, but this is almost irrelevant to the seasons. Instead, the temperature ...
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How badly could someone be injured by concentrated sunlight?

Recently-ish, I stumbled across an interesting short story (by way of Science Fiction & Fantasy Stack Exchange) where a soccer referee is apparently incinerated by concentrated sunlight. Where ...
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Why is pale coloured skin said to absorb more UV?

Many resources state that light skin/pale skin absorbs more UV than dark-colour skin. Doesn't black absorb maximum radiation? For an example, see this article: Natural selection therefore ...
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803 views

Why does large curvature of spacetime imply high temperature?

I`ve just stumbled about a sentence which says that high curvature of spacetime implies that any matter present is at high temperature. This somehow confuses me, so my probably dumb question(s) are: ...
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Is there a temperature at which ice is denser than water?

Normally ice would float on water because its density is less compared to that of water as a liquid. But is it possible that its density will increase due to a very low temperature or is ice in any ...
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938 views

How hot is the water in the pot?

Question: How hot is the water in the pot? More precisely speaking, how can I get a temperature of the water as a function of time a priori? Background & My attempt: Recently I started spend ...
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Milk or sugar first to maximize temperature of a hot cup of tea?

If there is a hot cup of tea and we were asked to add milk and sugar, which mixing order would make the hottest tea? I personally think that the order doesn't matter, since sugar wouldn't change the ...
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Perpetual motion machine of the second kind possible in nano technology?

First of all sorry for my English - it is not my native language. During my engineering studies at the university the thermodynamics professor told us that the "second law of thermodynamics is not ...
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988 views

Is temperature of a single molecule defined? [duplicate]

Is temperature of a single molecule defined? This question just cropped up in my mind as I have often heard of laws being violated when it comes to the scale of a single molecule. Does this happen in ...
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Does tea stay hotter with the milk in it?

A little thought experiment, similar to this one: Imagine you are making a cup of tea when the door bell rings. You've poured the boiling water into a cup with a teabag in it. As you're just about to ...
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955 views

What leads to the existence of critical temperature?

We know that $T_c$ is the temperature above which no amount of pressure could force a gas to liquefy. But why is this? Somehow I don't buy the point that the gas molecules exert too much pressure ...
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Is energy the ability to do work?

Here was my argument against this, the second law of thermodynamics, in effect says that, there is no heat engine that can take all of some energy that was transferred to it by heat and do work on ...
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Why does maximal entropy imply equilibrium?

From a purely thermodynamical point of view, why does that entropy have to be a maximum at equilibrium? Say there is equilibrium, i.e. no net heat flow, why can the entropy not be sitting at a non-...
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Hot water freezing faster than cold water

This question has puzzled me for a long time. There is already a question like this on Physics.SE. John's answer to the question seems quite satisfying. But when I googled the cause I found this and ...
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Can entropy be equal to zero?

I've searched for it but I only found contradicting answers from "scientists": Dr. David Balson, Ph.D. states: "entropy in a system can never be equal to zero". Sam Bowen does not refutes the ...
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What happens to ice cream when you stir it?

I hope this is the appropriate forum for my question. I also considered posting it in the chemistry forum. When I eat ice cream I often stir it into a texture similar to that of soft serve. During ...
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Which direction does air flow?

I remember learning this in high school, but have forgotten it, and can't seem to find it anywhere online. Air travels from areas of high pressure to low pressure...correct? So if I have a cold room ...
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874 views

Intuitively, why is a reversible process one in which the system is always at equilibrium?

A process is reversible if and only if it's always at equilibrium during the process. Why? I have heard several specific example of this, such as adding weight gradually to a piston to compress the ...
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Recommendations for Statistical Mechanics book

I learned thermodynamics and the basics of statistical mechanics but I'd like to sit through a good advanced book/books. Mainly I just want it to be thorough and to include all the math. And of course,...
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How cold does it need to be for spit to freeze before hitting the ground?

What is the dominant form of heat transfer between warm water and cold air? If a $100 mg$ drop of water falls through $-40 C$ air, how quickly could it freeze? Is it credible that in very cold ...
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Maxwell's Demon Constant (Information-Energy equivalence)

New Scientist article: Summon a 'demon' to turn information into energy The speed of light c converts between space and time and also appears in $E=mc^2$. Maxwell's Demon can turn information ...
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565 views

Is the liquid/solid line infinite?

Starting from the triple point, is the melting line between solid-phase and liquid-phase infinite? If not, why does it end? Because pressures are so high that classical inter-molecular interactions ...
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903 views

Why isn't temperature frame dependent?

In (non-relativistic) classical physics, if the temperature of an object is proportional to the average kinetic energy ${1 \over 2} m\overline {v^{2}}$of its particles (or molecules), then shouldn't ...
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938 views

How do greenhouse gases trap heat?

I am looking for a molecular-level understanding of the greenhouse effect. What is it about the carbon-dioxide molecule (and methane, and water, etc) that is different from other gasses (particularly,...
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Principle of Caratheodory and The Second Law of Thermodynamics

Background Constantin Carathéodory formulated thermodynamics on a purely mathematical axiomatic foundation. His statement of the second law is known as the Principle of Carathéodory, which may be ...
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Nonequilibrium thermodynamics in a Boltzmann picture

The Boltzman approach to statistical mechanics explains the fact that systems equilibriate by the idea that the equillibrium macrostate is associated with an overwhelming number of microstates, so ...
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Is there a relativity-compatible thermodynamics?

I am just wondering that laws in thermodynamics are not Lorentz invariant, it only involves the $T^{00}$ component. Tolman gave a formalism in his book. For example, the first law is replaced by the ...
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383 views

Equation of state of cosmic strings and branes

I'm sure these are basic ideas covered in string cosmology or advanced GR, but I've done very little string theory, so I hope you will forgive some elementary questions. I'm just trying to fit some ...
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LED Thermal Modeling (How to solve heat equation with constant heat source)

I have a mechanical design with LEDs that generate heat. I want to estimate the temperature at the LED junction vs. time, but especially at steady state. Knowing the LED voltage drop and current, I ...
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532 views

Can we detect whether food has previously been heated in a microwave oven?

An acquaintance told me that she refuses to eat microwaved food because she read that the microwave changes the molecules of the food somehow. Her statement is vague and her sources are dubious but I ...
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Why does hot oil explode when pouring water on it?

What is the reason that hot oil makes sound and explodes when water is poured on it?
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Is it theoretically possible to reach 0 kelvin?

I'm having a discussion with someone. I said that it is -even theoretically- impossible to reach 0K, because that would imply that all molecules in the substance would stand perfectly still. He said ...
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How does heat actually stay kept in the carbon molecules in the atmosphere? [duplicate]

We have all learned that the earth is getting heat up because of the CO2 and CO molecules absorbing heat. However, how is heat actually kept in those molecules. When photons heat them up, their ...
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What equation of state is needed for liquid states?

I'm familiar with the ideal gas law $$PV=nRT$$ but I don't think it applies to liquids like water. If I'm wrong, please correct me! If I'm right, then what equation of state applies to liquids such ...
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Why does pizza cheese seem hotter than the crust?

When I eat hot pizza or a melted cheese sandwich, the cheese feels a lot hotter than the crust or bread: in particular, the cheese might scald the roof of my mouth. but the crust will not. Is this ...
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Is it more efficient to stack two Peltier modules or to set them side by side?

Is it more efficient to stack two Peltier modules or to set them side by side? And why? I have a small box that I want to cool down about 20 K below ambient -- cold, but not below freezing. (I want ...
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The difference between heat and temperature

So as I understand it, heat energy of an object is the SUM of all the kinetic energies of the molecules of the object (upto constant factor). The temperature on the other hand is the AVERAGE of the ...
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Definition of the entropy

In physics, the word entropy has important physical implications as the amount of "disorder" of a system. In mathematics, a more abstract definition is used. The (Shannon) entropy of a variable $X$ is ...
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Does placing a lid on a pot affect the rate of boiling?

On the subject of cooking, someone once told me "If you have too much water in your pot after cooking a dish, just turn up the heat and let it boil without a lid for a few minutes". Now I've thought ...
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Why is black the best emitter?

Why are emitters colored black better emitters than other colors? Why is white a worse emitter?
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610 views

If temperature is average KE per particle, and heat is total KE of all the particles, how can molar heat capacity vary?

If temperature is defined as the average kinetic energy per particle, and heat energy is defined as the total kinetic energy of all the particles (or more strictly, heat transferred is the total ...
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Would a perfectly clean and perfectly smooth champagne glass have no bubbles?

My understanding is that nucleation sites for bubbles in a champagne glass are either due to defects in the glass or due to fibers in the glass. (See this article for details on that statement.) Does ...
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Axioms behind entropy!

The concept of entropy is very ubiquitous, we learn about its uses starting from Information Theory (Shannon entropy) up to its basic definition in statistical mechanics in terms of number of micro-...
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What happens when you heat vodka in a microwave?

Since ethanol has a lower dielectric constant than water would the water heat up and boil before the ethanol? Would the water transfer heat to the ethanol and, since ethanol has a lower boiling point, ...