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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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 ...
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1answer
47 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 ...
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2answers
60 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 ...
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18 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 ...
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3answers
83 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 ...
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47 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 ...
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3answers
86 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 ...
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1answer
62 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 ...
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1answer
70 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 ...
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4answers
933 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 ...
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1answer
362 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 ...
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1answer
34 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 ...
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47 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 ...
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2answers
40 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 ...
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2answers
45 views

Rapid/ Slow Expansion in Gases

How is rapid expansion of gases different from slow expansion?
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28 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 ...
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4answers
977 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 ...
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1answer
56 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 ...
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1answer
48 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 ...
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1answer
30 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 ...
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2answers
88 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 ...
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1answer
30 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 ...
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1answer
49 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} + ...
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1answer
199 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 ...
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1answer
59 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 ...
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2answers
24 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 ...
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70 views

Why does specific heat increase with temperature?

Except for monoatomic molecules, specific heat increases with increase in temperature. Why?
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26 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 ...
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1answer
178 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 ...
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1answer
46 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 ...
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1answer
32 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 ...
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2answers
143 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 ...
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1answer
68 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 ...
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1answer
52 views

Preventing Heat Escape

Is is possible to completely prevent heat from escaping from a closed container? Here is a diagram of vacuum flask, which tries to implement the design - Vacuum Flask prevents heat from escaping ...
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1answer
37 views

Hot water from a faucet

Why does hot water come out of a faucet cloudy white? The cold water comes out clear, but if you turn the hot water tap on, it'll be clear until it gets hot and then turns a cloudy white colour. ...
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1answer
58 views

Heat equation with heat loss to surroundings

I am trying to model one dimensional heat diffusion within a uniform copper rod with insulated ends. In addition, I am including a term that models the heat loss to the surroundings from the lateral ...
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1answer
92 views

Is temperature the speed of electrons?

Back in the middle school (which I guess was about 10 years ago) I remember being taught that the temperature of an atom is basically the speed of electrons circling the nucleus which kinda made sense ...
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3answers
56 views

Work in the First Law of Thermodynamics

The First Law can be stated as $\Delta U=Q-W$, where $W$ is the work done by the system. My question is what kind of work $W$ includes. $W$ certainly includes $PV$ work, i.e. expansion and compression ...
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1answer
46 views

Classical Mechanics — Sign of work done

It seems that work has two possible ways to decide it's sign: Whether you take the perspective of the system or the surrounding (whether you consider work done on the system as positive, or work done ...
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1answer
60 views

Relation between Von Neumann entropy (and other entanglement measures) and thermodynamical entropy

Suppose I have a bipartite system (with Hilbert space $H = H_a \times H_b$) and the following state: $$\sigma = \sum_{n} \frac{e^{-\beta E_n}}{Z} \rho_n$$ where $Z = \sum_n e^{- \beta E_n}$ and ...
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0answers
18 views

Dependence of latent heat on pressure

It is known that the latent heat of vaporization increases as external pressure decreases. What is the cause of this phenomenon?
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51 views

Is possible to synthesize diamond at relatively lower pressures (6 to 7 GPa vs 12 GPa)?

Pure binderless nanopolycrystalline diamond can be produced from graphite when the graphite is treated with more than 12 GPa pressure and at least 2100°C temperature . If we treated graphite or ...
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1answer
56 views

Few doubts about saturated vapour pressure and unsaturated vapour pressure

I have some sort of confusions towards saturated vapour pressure and unsaturated vapour pressure.. So let me give you those. What is exactly saturated vapour pressure and unsaturated vapour ...
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1answer
27 views

Can I interpret Avogadro's principle of gases from the state equation (ideal gas law)?

Considering the molar form of the ideal gas law I can solve for the ratio of some gas volume, $V$ divided by the number of gas particles, $n$ in mols $$\frac{V}{n}=\frac{RT}{P}$$ And $R$ is the ...
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0answers
30 views

Sign convention thermodynamics

Say a system is inside a volume $V$ with surface normal vector $n$ pointing out from the volume. Then there are force vector fields (nonconservative and conservative) depending on parameters external ...
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1answer
58 views

How much a juice maker increases the temperature of the product?

Recently I asked on skeptics if cold pressed juice is higher in nutrients than one from centrifugal juicer and one of the claims is that the centrifugal juicer heats the juice enough to destroy ...
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1answer
50 views

Gough-Joule effect in rubber band

When a stretched rubber band is heated, surprisingly, its tension will increase. What is the physics behind this?! Another thing. The Entropic spring model says, for a good specimen, that the ...
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0answers
33 views

Measuring variation of saturated vapour pressure with temperature

Is it possible to measure variation of saturated vapour pressure of water with time.I just hesitate about it.My suggested procedure which is incomplete is given below Procedure that I would like to ...
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1answer
40 views

steady state and thermodynamic equilibrium

What is the difference between a system being in a steady state and thermodynamic equilibrium ? Can a system be in steady state but not in thermodynamic equilibrium and vice-versa?
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33 views

Efficiency of an Internal Combustion Engine

This question is about How correct are those comments on efficiecy of internal combustion(IC) engines which calcuate it using 2nd law of thermodynamics.The maximum efficiency of a heat engine can be ...