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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Cooling down to absolute zero by radiation

Consider a system consisting of a gas, it is put in a container which is permits transmission of all kinds of electromagnetic waves. If this system is isolated and put in a perfect vacuum, and left ...
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17 views

Heat loss by radiation reference

In our lab practice, we measured the rate of heat loss of a copper plate in atmospheric pressure and the rate of heat loss of the same plate in high vacuum ($\sim 10^5 torr$). So all I could find for ...
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1answer
45 views

How does covering a hot bowl of soup prevent heat losses?

Recently I took out some soup to eat and got a call from a friend. I covered it with a plate and when i came back later, it was still hot. While i was eating, i wondered how does covering this hot ...
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30 views

probability of striking the circular ring by gas molecules

In kinetic theory we use probabilistic case to derive pressure, no. Of molecules having speed c to c+dc or in such cases.and to derive such equations we introduce a term called "SOLID ANGLE" I come ...
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220 views

In a Monte Carlo NVT simulation How do I determine equilibration

I'm running an NVT (constant number of particles, volume and temperature) Monte Carlo simulation (Metropolis algorithm) of particles in two dimensions interacting via Lennard-Jonse potential ($U = ...
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4answers
3k views

If we feel it's hotter when humidity increases, then why do we feel it's colder when inside water?

When the humidity in the air is high, we sweat more and feel it's hotter than when the humidity is lower. So why don't we feel it's hotter when we go inside water, where the water content is much ...
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1answer
209 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 ...
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1answer
261 views

Boltzmann Distribution of Electrons in Confining Potential

I have a particle simulation wherein many non-interacting electrons are trapped in a electric potential well. I would expect, and therefore I initialize according to this, that the electrons would ...
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526 views

How does the dissolution of salt affect the solution density?

Suppose you have a container of water as a solvent and you a certain amount of salt as a solute sitting at the bottom of the container that has yet to start dissolving. Supposing temperature and ...
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42 views

Why do you feel “hot” at a certain temperature? [on hold]

I think it's safe to say that in general 90$^\circ$F or even 85$^\circ$F is pretty hot. Your body ends up having to sweat or use some mechanism to release heat. I looked up the surface temperature of ...
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1answer
51 views

How cold does this ice have to be to freeze this water bottle solid?

We are at sea level in a room that is 21 celsius. We have 1 liter of sterile water with a temperature of 21 celsius in a normal plastic bottle. We have a 20 liter bucket of ice cubes, consisting of ...
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26 views

How to calculate the energy transfer between working coil and working piece and dissipated energy of working piece in induction heating?

For who don't know how does induction heating work, a short description can be found here. However, my question is about physics. Assume I have a coil inductor calculated carefully 50 uH as below: ...
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2answers
59 views

How much faster are airmolecules going when the temperature raise from 15 to 25 degrees C?

As far as I know the temperature of the air depends on how fast the airmolecules are moving. But what is the increase of speed (in km/h) of those air molecules?
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129 views

Do gravitational waves have entropy?

We know, according the current understanding of black holes and General Relativity, as well as quantum fields in General Relativity, that black holes have an entropy proportional to the area of the ...
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4answers
17k views

After what speed air friction starts to heat up an object?

I understand that air friction cools off an object at low speeds. For example, if you blow on a spoon of hot soup, it cools off. Or if you swing a hot frying pan in the air, it cools off faster. But ...
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133 views

Why do liquids exist?

This post asks why matter exists in three phases. Most of its answers explain the existence of liquids with some variant of the following: liquids happen when thermodynamic conditions, temperature ...
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2answers
63 views

Blocks releasing heat energy [on hold]

If you had two blocks, two different sizes yet the same temperature. Which one would release the most energy in the shortest amount of time and why?
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1answer
174 views

Entropy of the cosmological constant and the laws of thermodynamics?

Convention The convention being used is: $ A_{C} = $ The classical variable Premise Consider the following toy-model universe: A universe with a positive cosmological constant. Basic ...
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1answer
30 views

A system with temp T is in contact with a reservoir of temp T. Would the system ever take in energy and expand (do work) in this situation?

The context is explain a Carnot cycle and how to get work from a system. Its starts by saying the system is in equilibrium with its surroundings, but then it take in some energy Qin. How does ...
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1answer
34 views

Why does stagnation pressure reduce across a normal shock?

I am seeking an explanation for this graph where the subscript "1" refers to the supersonic region and the subscript "2" refers to the subsonic region present beyond a normal shock. The static ...
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2answers
53 views

What is the nature of equilibrium between water and air in a sealed container that is heated above 100C?

In the case of a single substance (water), looking at the phase diagram is enough to conclude what happens upon heating: (source: WolframAlpha) But what if I have water and air (or some other gas) ...
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59 views

How much time it takes to boil water in a rigid body?

I have a question that bothers me. If we have a rigid container containing water at $P_1 = 1$ $atm$ and $T_1 = 25$ $°C$. If we add an electric resistance to heat the water inside, we go through ...
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3answers
6k views

How to calculate fluid's temperature change in a pump?

To calculate the pressure at the outlet of a pump we use pump performance characteristics i.e. charts giving pump head as a function of volumetric flow. When the fluid flows through a pump, it's ...
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2answers
264 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 ...
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2answers
51 views

Dissipation and first law of thermodynamics

Consider the following situation: a certain gas is contained in a well-insulated cylinder with a well-insulated piston head. Now, in this case the piston is not frictionless. In order for the piston ...
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6answers
6k views

How did my candle wax crawl up the sides of the jar?

I have an Ikea candle which has sat on my bookshelf in the sun for >5 years. Aside from an hour or two shortly after I bought the candle, I have not burned the candle regularly (in fact, the wick is ...
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3answers
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?
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2answers
113 views

Why is the net entropy change of an irreversible engine positive?

In a Carnot engine the net entropy changein a cycle is zero. But in an irreversible engine operating between two temperatures the net entropy change in a cycle is positive. As I have understood, this ...
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2answers
78 views

Maxwell velocity distribution, in 1D or otherwise

I learned from my textbook that Maxwell's velocity distribution gives: $$v_{rms} =\sqrt{\frac{3kT}{m}}$$ $$v_{avg} = \sqrt{\frac{8kT}{\pi m}}$$ Presumably this is for a three dimensions. This confuses ...
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50 views

Gibbs' Free Energie

What terms are needed to consider to create a rabbit out of nothing and place it in the classroom? Does this caption answer the question?
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60 views

Is the concept of work only defined in mechanics?

I'm studying energy and work, so far it looks like work only makes sense in kinematics (objects that move), but energy makes sense in many other ways (electric, thermodynamic, mechanic). Is work a ...
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3answers
76 views

Is this definition of work right?

My thermodynamics textbook defines work as follows. Work is motion against an opposing force. But this definition of work doesn't imply that work is done in accelerating a body does it? So is ...
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1answer
22 views

Inward heat flow

Firstly, is inward heat flow the same as inward heat flux? and which types of substances (e.g solid , liquid, gas) can inward heat flow occur in when the temperature remains constant?
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2k views

Why did the microwave oven only heat my coffee half as much as expected?

A sticker on my microwave oven states its output effect to be $750\ \mathrm W$, which is $180$ calories per second. This means that heating $250\ \mathrm g$ of water by one degree Celsius would take ...
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357 views

Heat flow in a hollow cylinder

Consider a hollow cylinder of different outer radius and inner radius and two different temperatures are maintained at the outer and inner surfaces such that inner temperature is higher. Because of ...
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0answers
78 views

Entropy of unattended music streaming and other useless processes

I just realized that on my work pc, I had an internet music streaming service turned on for the last week, but muted (=useless). I was wondering how much entropy in excess was generated by ...
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0answers
21 views

How exectly does Molecular potential energy change in change of state?

I have learn some basic knowledge of Heat in my class, and I got confused when dealing with the change of state. Basically, what the textbook say is that the molecular kinetic energy keeps constant ...
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1answer
77 views

Are all diffusion-like processes described as wave-like in relativity-compatible formulations?

Citing from Wikipedia's article on relativistic heat conduction: For most of the last century, it was recognized that Fourier equation (and its more general Fick's law of diffusion) is in ...
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1answer
193 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 ...
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1answer
6k views

How does smoke move in the air and how can I direct it so it will go to a place I want it to go?

Let's assume a close room with 1-2 people who only one of them smoking cigarette. What is the equation describe the smoking spreading? is it diffusion? what are the parameters is so? Is there a ...
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1answer
398 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 ...
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2answers
2k views

Burning VS Melting: What is the relation in the atomic/molecular structure?

This has never been asked before on this site, so I thought I would ask this to help future searchers, passerbys, or others understand this better. What are the key differences between burning ...
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2answers
78 views

Understanding Gibbs $H$-theorem: where does Jaynes' “blurring” argument come from?

According to this Wikipedia article, the $H$-theorem was Boltzmann's attempt to demonstrate the irreversible increase in entropy in a closed system starting from reversible microscopic mechanics. ...
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38 views

Question about turbines logic

In thermodynamics, according to some book exercises, a fluid can enter a turbine and come out with greater speed compared to the inlet speed. It makes sense looking at the conservation of energy ...
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1answer
139 views

Calculate the entropy per atom in Bohmian Mechanics

Bohmian mechanics description of a large number of interacting atoms would require a large phase space due to the large number of classical degrees of freedom. The entropy per atom is given as the ...
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2answers
702 views

Hysteresis and dissipation

Hysteretic phenomena are often linked to dissipation. When there is an hysteresis loop, the dissipated energy can usually be computed as the area of the cycle. For example, in ferromagnetic ...
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2answers
344 views

How to understand the indeterminate process in thermodynamics?

Consider a closed composite system with an internal movable adiabatic wall. If we release the piston, thermodynamics cannot determine the final equilibrium state (the temperature cannot be ...
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33 views

estimating deviations from ideal gas behaviour

How can one estimate the pressure at which argon atoms show deviations from ideal gas behaviour due to the finite size of the atoms? I have tried Taylor expanding the hard sphere gas equation: ...
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2answers
46 views

Is flow energy the same as work?

Studying thermodynamics I face this following text from Cengel's book. Throttling valves are usually small devices, and the flow through them may be assumed to be adiabatic (q = 0) since there is ...