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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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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39 views

Why does specific heat increase with temperature?

Except for monoatomic molecules, specific heat increases with increase in temperature. Why?
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11 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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93 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
29 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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Mixture of Gases in kg-mol; Find Temperature [on hold]

A one cubic container contains a mixture of gases composed of 0.02 kg-mol of oxygen and 0.04 kg-mol of helium at a pressure of 220 kPa. What is the temperature of this ideal gas mixture in degrees ...
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1answer
19 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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22 views

How do I determine the heat conductivity of a material? [on hold]

I have a cup. I want to determine how much heat is transferred between the inside contents (boiling water) and the outside surroundings. What kind of information and how do I determine how to ...
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2answers
113 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
32 views

Will my induction hob be powerful enough? [on hold]

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
29 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
27 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
47 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
77 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
47 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
42 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
43 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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40 views

Proving $-\frac{\partial P}{\partial V}|_{T,N}\geq0$ [on hold]

I have obtained the following condition from the entropy maximum principle: $$\left.\frac{\partial^2U}{\partial V^2}\right|_{S,N}\left.\frac{\partial^2U}{\partial ...
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11 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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37 views

What time of day to run the air conditioner? [on hold]

I live in the Rocky Mountain West, where the summer temperature fluctuation from low to high is typically 30-40 degree F. We have a seldom used house on the market. We would like the temperature to ...
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2answers
42 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
25 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
26 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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45 views

Equipartition theorem and virial theorem differences?

The classical virial theorem and the classical equipartition theorem are clearly related. A version of the virial theorem is, \begin{equation} \bigg\langle \sum ^{3N}_{i=1} x_i\frac{\partial ...
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28 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
55 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
25 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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Conduction of heat [closed]

Choose the correct statement(s): A. Conduction of heat occurs in solids,liquids and gases. B. With increase of absolute temperature, a gas becomes a better conductor of heat. C. In solids the ...
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1answer
26 views

How can I find the temperature of a welded part of two metals? [closed]

Let's say you have two bars, different metals(Assume it's Iron and Copper) connected end-to-end(welded). The other end is Dipped(either Fe or Cu) to Icy Cold water and the other end is Steamed. How ...
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18 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
25 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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25 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 ...
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199 views

Will Neil Armstrong's moon boot marks really last for thousands of years?

This question concerns the residual heat (if any) contained within the Earth's moon. At the time of the Apollo moon landings, it was widely reported that the boot marks left by the astronauts would ...
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107 views

Is a larger, heated space easier or harder to ventilate if the heat source and ventilation are the same?

Imagine a well insulated room with a heat source inside. The room has two vents, which each have a fan. Cool air is drawn into the room through one vent, and warm air is pushed out the other vent. ...
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19 views

Maxwell relations | U goes down pressure?

Differentiating Helmholtz function $ A = U - TS $ with respect to $V$ we get: $$ (\frac{\partial A}{\partial V})_{\scriptscriptstyle T} = (\frac{\partial U}{\partial V})_{\scriptscriptstyle T} ...
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When is strain rate constant?

I have started a tricky problem involving strain rates. To simplify it I was wondering if I can assume the strain rate is constant (and therefore that the shear stress is constant with distance above ...
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51 views

Is a body of gas cooler in its upper portion as a result of gravity? [closed]

I read an article a couple of hours ago named Hydrostatic Lapse which makes the case for a phenomenon that I thought was well and truly confirmed; that gravity is responsible for the cooling of gas ...
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8 views

Reaction enthalpy-work relationship in a closed piston-cylinder assembly undergoing a chemical reaction

In an closed and insulated piston-cylinder assembly under constant pressure. From first law I should expect $-p(V_f-V_i) = U_f – U_i$ and thus $H_f = H_i$ and $h_f = h_i$. If an exothermic reaction ...
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30 views

Change in internal energy

One definition in my textbook states that total derivative of internal energy $dU$ has the form: $$dU = C_vdT +(\frac{\partial U}{\partial V})_{\scriptscriptstyle T}dV $$ Which I interpret this way: ...
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1answer
23 views

Heat loss during evaporation of a liquid boiling due to Bernoulli effect

this is my first post here. I watched this video https://www.youtube.com/watch?v=h5wQoA15OnQ and at 51 seconds it describes Bernoulli's effect of a drop in pressure resulting from an increased ...
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18 views

How accurate is the Callendar-Van Dusen equation?

... over 0 degC to 100 degC? The equation itself can be found here I can do a very accurate one point calibration of a 1/10 DIN PT100 sensor at 0 degC. If I use the equation to correct for non-linear ...
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1answer
37 views

Biological heat dissipation methods

If the human body is facing temperatures above it's own temperature in a humid environment eg. a rainy jungle above 37 degree celsius, are there any mechanisms that still allows heat dissipation? I ...
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47 views

How much sunlight would 'fit' through a fibre optic cable?

Say a parabolic mirror were used to focus the full sunlight spectrum into a single strand of optical fibre. Assuming ideal conditions (perfect reflecting surface, focal point smaller than diameter of ...
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1answer
22 views

Determining the final state of the gas in the tank

Suppose there is air of mass m1 in an insulated tank at temperature T1 and pressure P1. 0.25m1 of air is released through a valve attached to the tank. Find the final temperature, T2 and pressure ...
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21 views

Must irreversible heat transfer be quasistatic?

Suppose there is an isolated system composed of two subsystems $A$ and $B$ in thermal contact with each other, but mechanically and diffusively insulated from each other. The system starts off with a ...
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39 views

Does mixing violate conservation of energy?

If two fluids in an isolated system mix, the entropy of the system increases. The volume and the number of particles in the system, however, are constant. Thus $$dU=TdS+PdV-\mu dN=TdS>0$$ which ...
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1answer
38 views

Tap water in the cold glass

It is fairly long time I was in school and I was particularly bad at thermodynamics. This is an question I was trying to comprehend. I have 500ml of tap water @ 20°C. I pour it into heavy glass ...
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1answer
58 views

Calculation of entropy change in irreversible cycles, meaning of $\delta Q/T$ in irreversible processes

Lets take the two cycles in the pictures working with an ideal gas. We perform one, and than perform the other. The cycle is made reversible by making the gas exchange heat with a heat bath having ...
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2answers
44 views

unchanged temperature of balloon inside freezer

I'd tried to put a balloon in the freezer and after enough time (several hours), I took it out and noticed that as I touch it that it's temperature did not drop down . I took an empty balloon ( not ...
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1answer
42 views

Illustration of heat processes

In isothermal process the work produced in a cyclic transformation is the sum of the small quantities of work $ \delta W$ produced at each stage of the cycle. This description of work I picture, for ...