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 (1)

1
vote
1answer
35 views

Is it true as entropy increases things become more symmetric?

Is it true that as entropy increases in a particular domain (say, the universe or a given box) so do the symmetries within this domain? Are there exceptions? Say I'm looking at a rotational symmetry. ...
4
votes
1answer
227 views

What is the entropy of a mixed state in classical physics?

Consider a classical system which admits certain macroscopic level of description. It is known, that for two pure states $\omega_1$ and $\omega_2$ on this level of description the entropy of the ...
1
vote
1answer
25 views

Internal energy in phase transition

As I understand, in the process of state transition (fusion or vaporization) the temperature remains constant for the duration the process is happening. The internal energy is a function of only ...
2
votes
1answer
65 views

Is the energy per degree of freedom $\frac{1}{2}kT$ in relativistic systems?

The equipartition theorem says that the mean energy per degree of freedom is $\frac{1}{2} kT$. Is this result relativistically correct?
0
votes
1answer
34 views

relation between speed and temperature in relativistic gas

What is the correct formulation of the relation between the speed and temperature in the relativistic kinetic gas? I have found one mentioned in problem 3.24 of the third edition of Pathria's ...
1
vote
4answers
145 views

Is amount of entropy subjective?

From all sources I have seen it follows that the proof you can't decrease the amount of entropy in the Universe is given only statistically - the order is just one of the many ways how things can be ...
0
votes
1answer
43 views

first law of thermodynamics and conservation of energy

The first law of thermodynamics is referred to as a reformulation of the law of conservation of energy. I am not sure to fully understand this relationship. My way of picturing it is the following. ...
1
vote
0answers
41 views

Why can't the energy gained due to entropy be used for doing work?

Gibbs energy is defined as the energy 'available' to do work at constant temperature & pressure.The energy required to make the system from none under constant pressure is the enthalpy, that must ...
1
vote
3answers
94 views

Really how does the entropy of the universe increase?

Universe means the system along with its surroundings. I have always got this statement while studying the second law; be it a thermodynamics book(Sears, Salinger) , physical cihemistry book(Atkins, ...
3
votes
0answers
71 views

Free energy of coupled classical harmonic oscillators

I'm looking to find the thermodynamic (NVT) free energy of a classical coupled harmonic oscillator system such as the one below: (image taken from ...
0
votes
0answers
19 views

How is the first law of black hole thermodynamics formulated for a non-vacuum solution with event horizon?

How is the first law of black hole thermodynamics formulated for a non-vacuum solution with event horizon?
0
votes
1answer
53 views

Does a venturi injector contradict the 2nd law of thermodynamics?

The picture below shows a venturi injector. When the water flow enters the narrower cross section its velocity increases and its pressure decreases. Subsequently, fluid is sucked (or injected) into ...
-2
votes
0answers
25 views

How does large dof of gas particles affect temperature?

Supposing gas particles that could have instead of 7 dofs, a few hundred dofs, how would gamma change? I suppose it would still be (7/2)R? And how easy would be to change temperature of such a gas?
-1
votes
1answer
67 views

What are the distributions of electron speeds (a) in a star? (b) in a planet?

Ideally I would like to have an x-y graph of (x) speed relative to centre of mass of the body (star or planet) against (y) the number or percentage of electrons having that speed at a given moment in ...
0
votes
0answers
19 views

How to calculate electrical and thermal conductivity, enthalpy and density of plasma column in air for a series electric arc?

I am modeling an electric arc according to "Lowke's Simple theory of free burning arc". Its a very interesting theoretical arc model and I want to implement it in Matlab/Simulink. But here, the arc ...
0
votes
2answers
70 views

Uniqueness of solution of Laplace's equation

Consider steady-state temperature in a rectangular plate; we get solution when we solve Laplace's equation. In the midway of solving this equation, we take linear combination of basic solutions and ...
0
votes
2answers
55 views

Thermodynamics - Possibility of Cold radiation

I am no physicist, let’s just get that out in the open, I'm just a guy with an interest in this area. One thing I have learned in my limited examination of the natural world is that things tend to ...
1
vote
1answer
36 views

Isothermally Adding Heat

This makes absolutely no sense to me. My physics book states the following (University Physics 12th ed, Pg 650) Suppose we want to change the volume of a certain quantity of an ideal gas from 2.0 ...
2
votes
2answers
40 views

Gibbs phase rule and degrees of freedom at the triple point / triple line

The Gibbs phase rule tells me that at a substance's triple point, where there are 3 phases in equilibrium, there should be 0 degrees of freedom. Based on my understanding, that means there should be 0 ...
0
votes
0answers
9 views

How to find specific volume of air beyond normal Psychrometric table

During a calculation of direct-heat dryer, I have ended up with following situation. Inlet temperature of solid TS1 = 35.5 oC Inlet temperature of air TG2 = 615.0 ...
1
vote
3answers
46 views

Calculate pressure with the ideal gas law or $\rho gh$?

In a container the pressure on the walls due to a gas can be calculated using the ideal gas law $\bigl(pV=NRT\bigr)$. However, for a column of water, or the pressure at earth's surface due to a ...
0
votes
0answers
45 views

Was the impossibility of the second degree perpetuum mobile in the General Relativity ever proven?

Somewhere I've heard, that gravity often likes to work against the entropy. For example, the surprisingly low temperature of the black holes. Or see the gravitational separation of different elements ...
0
votes
3answers
80 views

Can higher level animals have lower entropy than the food they consume?

If there is plant source of energy 100Cal and an animal source of energy 100Cal for a human being, where the animal derived that energy from a similar plant source, can we say for sure that the animal ...
5
votes
1answer
48 views

energy efficiency - dryer vs hang+dehumidifer

When I have wet clothes coming out of the washing machine, I can either tumble-dry them in an electric clothes-dryer, or I can hang them to dry. But I can only hang them in a basement. The basement ...
0
votes
1answer
63 views

Temperature of planets without atmosphere

I am wondering how come a planet without atmoshhere loses heat in space when the space around it is a vacuum. In my understanding for one object to lose heat it must have contact with another ...
2
votes
4answers
922 views

Does stopping the same bike and rider at the same velocity with the front brake require less energy than the back brake?

It's the same body made by the rider and the bike moving at the same speed. So, even though braking on the front/back alters the normal forces on the opposite wheels thus creating more friction with ...
3
votes
1answer
338 views

Why do we ignore rotational energy in monatomic gases? [duplicate]

I understand that the average energy of each degree of freedom in a thermodynamic system is $\frac12kT$. And so, for an ideal monatomic gas, there are three degrees of freedom associated with the ...
0
votes
1answer
29 views

Find an expression for S(T,x) from tension and specific heat

I'm working on a problem from a Statistical Mechanics lecture series online, and on the homework, I hit a bump in this problem. Here is the problem set, and I'm asking about #1.c. Short version, we ...
1
vote
1answer
41 views

How do I calculate the change in water temperature as a function of depth?

Let's say I have ground water at a depth of $3000m$ at $50^{o}C$. If I now pump this water up to the surface, the water pressure decreases from the $\pm 300 atm$ at that depth to $1 atm$ at the ...
1
vote
2answers
32 views

Finding the Enthalpy of an Ideal Gas given internal energy

I am trying to find a formula for tying things up. Given an ideal gas like helium or nitrogen gas (diatomic) how can I find its enthalpy simply given internal energy? I remember it was once taught in ...
0
votes
2answers
37 views

Rapid/ Slow Expansion in Gases

How is rapid expansion of gases different from slow expansion?
0
votes
0answers
27 views

Can I measure the volume of a locked room by pumping gas through keyhole and measuring its entropy?

Suppose that I have a locked room and a keyhole in the door and I want to measure the room's volume. Suppose also that I have some "magical" "artificial" inert gas A that doesn't interact with ...
13
votes
4answers
949 views

How does the heat death looks like from inside the system?

As this answer points out, any human would first freeze rather than experience the heat death. However, assuming hypothetically that we could make some robot live at such low temperature (or even ...
0
votes
1answer
50 views

Understanding the Carnot cycle

My textbook explains the Carnot cycle as follows: Heat is added to the boiler, where the steam inside expands isothermally at high temperature (T(High))--(both valves closed). The intake valve is ...
0
votes
1answer
42 views

Water enclosed in a vessel

Suppose I am taking water in a glass or metal or even something else. It s air tight and (so it is water tight). Now imagine, if I keep it heating and none of its molecule escapes from it, what am I ...
0
votes
1answer
29 views

Two glass bottles of water warming by different temperatures

A friend posed a question to me yesterday: if I have two glasses of 60 F water, would they heat at a different rate if one were in a 70 F room and one were in a 90 F room. Myself having some ...
2
votes
2answers
83 views

Should the weaker of two air conditions be switched off?

We have two airconditioning systems in the office. For the sake of this question, let us assume the following current conditions: AC1 (old) outputs air of 26°C AC2 (new) outputs air of 18°C Office ...
-3
votes
0answers
30 views

Buying books that are out of print [migrated]

I've just returned the book Principles of Modern Thermodynamics, by Bimalendu Narayan Roy* to the library. It is a terrific book which gave me a much greater understanding of thermodynamics than I ...
0
votes
1answer
25 views

Distinguishing Isentropic Process; Are all things in an insulated cylinder considered reversible adiabatic?

How much work is necessary to compress air in an insulated cylinder from 0.20m^3 to 0.01m^3. Use T1 = 20C and P1 = 100 kPa. I don't need to solution or the answer. I already have it. But I think ...
0
votes
1answer
48 views

Help recognizing partial differential equation

I would be very grateful if someone could tell me something about the following partial differential equation: $$ \frac{\partial U}{\partial t} = K * (\frac{\partial^2 U}{\partial r^2} + ...
7
votes
1answer
196 views

Are the electrons at the centre of the Sun degenerate or not?

Trying to find an answer to this question, I came across two different methods of determining whether electrons at the center of the sun are degenerate or not. The first method, used here, calculates ...
0
votes
1answer
57 views

How do we measure thermal energy?

My textbook says "The amount of thermal energy is found by measuring the temperature of the substance." However, how is this true? Temperature measures only the average kinetic energy of the particles ...
1
vote
2answers
19 views

Is air infiltration a type of convective heat transfer (convection)

I have a building / physics question... A major source of heat loss in homes and buildings is infiltration through cracks (warm air from inside seeping out). Wondering if this falls in the category ...
0
votes
0answers
57 views

Why does specific heat increase with temperature?

Except for monoatomic molecules, specific heat increases with increase in temperature. Why?
0
votes
0answers
15 views

Is Isochoric compression or expansion possible?

Stirling cycle is made of two isothermal and two isochoric processes. Heat is added isothermally, expansion and compression takes place isochorically, as given by the book. How can a gas be ...
7
votes
1answer
146 views

Why does hitting a cold bag of water freeze?

About 24 hours ago, I bought a box of 30 pieces water ice. I put them in the freezing compartment and when I came from work I was expecting a nice chilling ice. But when I opened the freezer, I saw ...
0
votes
1answer
43 views

Can the entropy of a part of a closed system become less than the initial entropy of the entire system?

I am reading Sir Roger Penrose's book "What came before the Big Bang?". Here, I came across a chapter where he talks about how sunlight provides us energy in low entropy and how through various ...
0
votes
1answer
25 views

What is the work done in isobaric expansion?

I'm really confused now... I thought the equation was $ W = \int PdV = P\Delta V $ since P is a constant and can be taken outside of the integral. But on the other hand, $ P = \frac{NkT}{V} $, so if I ...
4
votes
2answers
132 views

Can the Sun's core be treated as an ideal gas?

I know that a gas behaves more like an ideal gas at higher temperature, and that is very well achieved in the Sun's core. But also low pressure is needed for a gas to behave like an ideal gas, and the ...
1
vote
1answer
46 views

Will my induction hob be powerful enough? [closed]

I'm looking to buy an induction hob to heat some water and I would like to know if its going to be powerful enough. If so, can it be done in, say, 1 hour? Additionally, what power rating could I go ...