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

learn more… | top users | synonyms (3)

2
votes
1answer
46 views

How is 'Fog' in summer (sea-elevation) possible?

I am residing in New Delhi (pardon me for any irrelevant data I might include), and I noticed a really interesting thing. It's an average $30^{\circ}\mathrm{C}$ out here, and yet, most/some weather ...
0
votes
1answer
34 views

Is the relation between expansion of a liquid with temperature linear?

Say I have a liquid with certain volume. If I heat it, will it expand with a constant rate? $$ \frac{T}{V} = k.$$ It is true for gases, is it also true for liquids? And if yes then: is it true for ...
2
votes
1answer
2k views

Definitions in thermodynamics: temperature, thermal equilibrium, heat

I'm currently reading Fermi's "Thermodynamics" and I'm trying to grasp the (possibly different) right definitions for temperature, thermal equilibrium, heat. To clarify, I'm looking for definitions ...
-1
votes
3answers
102 views

Is this explanation for the Universe's low entropy at its origins plausible? [on hold]

I've been thinking about this, and it may sound very ludicrous (and it probably is), but I may have come up with a proto-explanation for it. I hope I won't come across as some misinformed perpetual ...
7
votes
3answers
94 views
+150

Fluids with critical point at ordinary temperature and pressure

Are there any fluids with critical point near STP or that are supercritical at STP? If not would it be feasible to design a molecule for a substance with critical point near STP using theoretical/...
0
votes
0answers
19 views

Heat transfer direction in fins

I'm unsure of what exactly is changing the heat transfer direction in the triangular fin. $$q_{x} = -kA(x)\frac{dT(x)}{dx} (1)$$ $$q_{x+dx} = -kA(x)\frac{dT(x)}{dx} - k\frac{d}{dx}[A(x)\frac{dT(x)}{...
-1
votes
0answers
21 views

How to calculate the heating power of a metal plate in nature?

I like to heat up a part of a metal plate to a given temperature. For that I want to use an electric heater. The metal plate is located outside in nature. For that I need to take in account the wind ...
3
votes
1answer
106 views

Is refraction of light a thermodynamic process?

Is refraction of light a thermodynamic process? Can it be explained by conservation of energy? If so, does temperature has an effect on refraction of light?
20
votes
12answers
8k views

What is entropy really?

On this site, change in entropy is defined as the amount of energy dispersed divided by the absolute temperature. But I want to know: What is the definition of entropy? Here, entropy is defined as ...
0
votes
1answer
69 views

What is meant by a “change in volume of a system”?

I keep getting confused when my professor talks about the change in volume of a system. Sometimes it seems as though he's talking about the volume of the gas and at other times he might be talking ...
0
votes
2answers
48 views

Heated and cooled air effects on combustion

In a turbocharged engine, an intercooler is installed to cool down the compressed air (apparently for better combustion). In contrast, in the power plant they use air preheater to heat up the air ...
0
votes
0answers
13 views

Are elements of statistical ensemble fixed or dynamic?

I will use the simplest example I can think of to explain what I am trying to understand. Consider a system with ~10^23 particles in an equilibrium with fixed values of pressure, volume and ...
13
votes
6answers
7k views

Why was the universe in an extraordinarily low-entropy state right after the big bang?

Let me start by saying that I have no scientific background whatsoever. I am very interested in science though and I'm currently enjoying Brian Greene's The Fabric of the Cosmos. I'm at chapter 7 and ...
16
votes
2answers
884 views

Does fluid speed affect liquid cooling?

If you have a liquid-based cooling system, like the loop in the picture below, does the fluid speed actually matter? I can see how cycling the liquid too slowly would be bad, since the fluid would be ...
2
votes
1answer
34 views

Extinction level meteor effects on Earth's crust pending on the surface area upon impact

Would it be possible to have a extinction level meteor hit Earth depending on shape to actually create minimal damage if turned on its thinnest area rather than hitting flat? The meteor would enter ...
1
vote
4answers
2k views

Specific heat capacity at constant volume VS constant pressure

For an ideal gas, why is the specific heat capacity at constant volume lower than the specific heat capacity at constant pressure?
18
votes
4answers
2k views

Why does water feel cooler than air?

My first assumption was based on "evaporation causes cooling" but I realized that it is not the case as it is cooler even if I am submerged under it. Are all liquids generally cooler than air ? Just ...
4
votes
2answers
3k views

Why does friction produce heat?

What causes two objects sliding against each other to produce heat? Why don't they generate visible light or something else?
5
votes
2answers
206 views

Is ergodic hypothesis in contradiction with the notion of equilibrium?

From wikipedia: In physics and thermodynamics, the ergodic hypothesis1 says that, over long periods of time, the time spent by a system in some region of the phase space of microstates with the ...
1
vote
1answer
52 views

Why is black hole entropy not an extensive quantity?

The Bekenstein entropy for a black hole is proportional to the surface area $A$ of the black hole $$ S_{BH} = \frac{k_B}{4 l_P} A $$ with the Planck length $l_P = \sqrt{\frac{\hbar G}{c^3}}$. The ...
2
votes
5answers
90 views

Is perfect thermal insulation possible?

Supposing someone says they have a sample of insulanium with the following properties: If you make a thermos out of insulanium, it will keep a drink hot or cold forever. If you put your hand on a ...
-2
votes
0answers
31 views

Why does depth and height replace volume in this problem? [on hold]

In the following problem, why does H/𝛿 replace V/V? The two ratios have different units. Is there something I'm missing here?
0
votes
3answers
95 views

How much water did I actually drink? [on hold]

Water expands at temperatures over $5^\circ\mathrm C$ strictly monotonic. If you now drink $1~\mathrm{L}$ water ($5^\circ\mathrm C$) which will expand in your body on $37^\circ\mathrm C$, did you ...
2
votes
1answer
123 views

What is the difference between thermodynamic and empirical temperature?

When I've studied Thermodynamics I did so in Callen's book and there the author talks about temperature as a single thing, which mathematically is simply defined as: $$T = \dfrac{\partial U}{\partial ...
5
votes
1answer
426 views

Conservation of energy when focusing black body radiation on another black body

This question about whether or not it is possible to focus black-body radiation to make something hotter than the radiation's source was answered mostly negative: the second law of thermodynamics and/...
3
votes
2answers
62 views

If we harvest energy generated by Coriolis Effect of the earth, will the earth slow down?

Coriolis Effect causes strong winds in the upper atmosphere, and it's purely due to differences in the linear velocity of Earth's rotation across latitudes. Now the Earth is spinning with the energy ...
0
votes
1answer
207 views

What is the relationship between liquid-gas expansion pressure and surface area to volume ratio?

If a set volume of liquid is heated above its boiling point, how does the pressure that that volume of gas generates relate to the surface area of the medium in which it is enclosed in. For ...
7
votes
2answers
250 views

Is the thermal conductivity of metals affected by magnetic fields?

Especially for a ferromagnet a magnetic field should have a field-induced band shift in the density of states but I wonder if this shift is big enough to be significant and affect the thermal ...
8
votes
4answers
415 views

Is information entropy the same as thermodynamic entropy?

Context In one of his most popular books Guards! Guards!, Terry Pratchett makes an entropy joke: Knowledge equals Power, which equals Energy, which equals Mass Pratchett is a fantasy comedian ...
1
vote
1answer
1k views

Otto cycle efficiency described in pressure ratio (instead of compression ratio)

The Otto cycle's thermodynamic efficiency is often described using the compression ratio: $$\eta_{th} = 1 - \left( \frac{1}{CR} \right ) ^ {k-1},$$ (where CR is the compression ratio, and k the ...
1
vote
1answer
137 views

Lindblad equation derivation

I'm reading A simple derivation of the Lindblad equation. It introduces a Hamiltonian for a system consisting of a principal system $S$, a heat bath $B$ and an interaction term: $\hat{H}=\hat{H}_S+\...
3
votes
1answer
35 views

Is it possible to quantify the work required to introduce order?

Is there a thermodynamic analysis that allows us to say "in order to introduce this much order into this subsystem, this much work must have been done on it by the rest of the system"? I assume that ...
0
votes
1answer
24 views

Heating water in a pot from a constant heat source

What are the equations used to calculate the amount of energy transferred from a constant heat source "like a stove" to a pot which would then transferred energy to water contained in that pot. I don'...
0
votes
1answer
103 views

Pressure derivative of bulk modulus

Hi all what is the definition of pressure derivative of bulk modulus if it is a pressure derivative of bulk modulus at zero pressure. if the pressure is zero how it is derivative by pressure?
3
votes
1answer
78 views

What is the temperature of water at the end of the pipe?

I need to solve the following problem for a practical application. Water, initially at temperature $T_0$, flows with a constant speed $v$ through a PVC tube of length $l$ and diameter $D$. The ...
0
votes
0answers
22 views

How to find the change in internal energy for a gas? [on hold]

So I'm given this problem, and for some reason when I solve for Q and delta U my answer is off, should be $\Delta U = 249.3J$ and $Q = 415.5J$ ...
6
votes
2answers
287 views

Rayleigh-Taylor Instability dependence on acceleration direction

I'm trying to bolster my understanding of the Rayleigh-Taylor instability, and I've gotten stuck on the point of which fluid (more or less dense) is being accelerated into the other. Cases of uniform ...
4
votes
7answers
3k views

Why the breath sometimes warm and sometimes cold? (2 different explanations!)

If you blow air against your hand with your mouth open, you feel warm breath. If you do with with your lips closed except for a small opening, you feel cold breath. One explanation from here says "...
0
votes
1answer
42 views

Does the shape of a meteor make any difference during an impact? [on hold]

Would the shape of the meteor make a difference on the impact? Like a Olympic diver would a spear shaped meteor make less damage to the surface of the Earth while creating more magma movement rather ...
0
votes
0answers
27 views

Is there a maximum temperature? [duplicate]

I have read about absolute zero. I understand that it is impossible to cool a system below absolute zero (or to absolute zero for that matter). However, is there a maximum temperature? My intuition ...
0
votes
0answers
8 views

Infer geophysical underground structure from thermal photography of the ground

Is it possible to determine (approximately of course) the geophysical structure of the underground under a certain region, using only a thermographic picture of the upper ground of the region ? The ...
1
vote
1answer
219 views

What causes a heat generating source to stabilize at a certain temperature? (Answered by myself, I think)

For example, we out a heat sink on a microprocessor to keep it cooler. I understand that if we run 100 watts of electricity through the microprocessor, it will generate 100 watts of heat, or 100 ...
4
votes
1answer
202 views

Thermodynamics, chaperones : How to model polymer fragmentation

Living polymers are well described by equilibrium statistical physics. Now I would like to consider a case were living polymers undergo fragmentation due to chaperones. I can think of a kinetic ...
1
vote
1answer
16 views

Why does a soda bottle foam or froth when dropped? [duplicate]

Secondly, if I do drop a soda bottle how long do I have to keep it for it to return to its original state or condition, I.e. safe to open without froth spraying everywhere; or is there some rule of ...
3
votes
0answers
61 views

Proving that the Boltzmann entropy is equal to the thermodynamic entropy

I've been trying to understand how we can equate the Boltzmann entropy $k_B \ln \Omega$ and the entropy from thermodynamics. I'm following the approach found in the first chapter in Pathria's ...
0
votes
1answer
115 views

How do the human heat sensors work?

I have been wondering about this particular issue for quite some time now. It feels like I should know this as a master's student in physics. The questions are, essentially, the following: What is ...
4
votes
0answers
101 views

Error in mathematics of collision theory [on hold]

I'm making lecture notes, and I felt that it would be important to explain some of the math behind collision theory. I come up with a problem, however. Here, I'm trying to show that the collision of ...
0
votes
1answer
54 views

Proof of ideal gas equation for container of arbitrary shape (kinetic theory)

While deriving ideal gas equation - we take gas molecules to be contained in a cubical container (convenient shape) , but how do we derive it for a gas inside some arbitrarily shaped container ? I ...
1
vote
2answers
121 views

Free expansion of an ideal gas

I am having trouble understanding the transient phase of an ideal gas expanding into vacuum. Firstly, the pressure of any gas is defined only when there is an instrument (barometer/ wall/ piston) ...
3
votes
1answer
52 views

Which temperature does $T$ in Clausius inequality ($\oint \frac{\delta Q}T\le 0$) refer to?

I got a little confused about the temperature in Clausius inequality. As you can see in this answer of Luboš Motl, it seems that temperature is the temperature of the system. But in some answers of ...