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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Optical element is heated by laser: is it possible to get oscillating heat distribution?

Imagine that we have thin optical element, which is irradiated by laser. Laser heats element, so there is some heat distribution in element. There is a heat sink through upper and lower element faces ...
3
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3answers
589 views

Will the water added to an ice piece freeze?

Water, at room temperature is poured into a hole made of a block of melting ice(kept at room temperature).I was wondering if the water will ever freeze? Thank you.
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1answer
214 views

Depalma Free Energy fields

Few years ago I read some papers about Free Energy, written by Bruce de Palma, a physicist who is said to be the inventor of the N-Machine, which is an device that works with free energy latent in the ...
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5answers
328 views

Is the cooling rate of a (very) cold object, sitting next to an AC higher or lower?

In more detail: If i have two soda cans, both are cooled to exactly 4 degrees celsius, And i put one in a 25 degrees room, and the other next to an AC vent set to 16 degrees. After three minutes, ...
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1answer
203 views

Can i use coils with compressed air to make a superconductor?

What im saying is inside pipes i am going to use compressing so that that in the places with low pressure they cool the superconducotor. is this possible? Can i use this concept to make ...
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3answers
458 views

Problem with an electricity / thermodynamics assignment

I've been trying to figure this one out for a while on my own, so I'd like to ask for your help if you could offer some. The task states: A heater made out of a wire with a diameter $R = ...
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3answers
383 views

Is the continuous transformation of energy from one form to another one free? Or it consumes some quantity of who knows what?

Sorry for the unclarity. I probably created some bias in your mind having tagged my question with energy-conservation and conservation-laws. I simply consider that, relatively independently of ...
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0answers
2k views

What are typical values of the critical thickness of insulation?

As most people who've had any elementary heat transfer course are aware, when insulating a pipe, wire, etc, there is a critical thickness for the insulation below which it causes greater heat transfer ...
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2answers
386 views

simulations at constant pressure-volume and constant volume-temperature

I have read some papers where the authors perform simulations at constant pressure and constant volumen or sometimes constant volume constant temperature. My question is when is it better to use one ...
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1answer
111 views

What are the patterns appear after kernel averaging?

Having a 2D map filled uniformly by random values (Figure:top-left) to demonstrate a disordered phenomena, the next maps are ...
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2answers
14k views

How does a change in temperature affect relative humidity

Assume that the air pressure and the amount of water in the air stay constant. How can I figure out how much a change in temperature affects the relative humidity?
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5answers
2k views

Entropy of radiation emitted into space

In several papers I see something equivalent to the following expression for the entropy of radiation given by an astronomical object such as the Sun (assuming the object can be approximated as a ...
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1answer
287 views

Trying to understand a step in deriving Maxwell-Boltzman statistics

In the Wikipedia article on Maxwell–Boltzmann statistics, there is a point in the derivation that stumps me. When I get to where $\displaystyle W=N!\prod\frac{g^{N_i}}{N_i!}$ is quoted as a count ...
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0answers
438 views

Heat equation and Bessel's function [closed]

Could someone please explain why if the time-independent heat equation can, via changing of variables, take the form of Bessel's equation that the $\sqrt\lambda$ should take the values of the zeros of ...
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1answer
7k views

Best way to solve P-V-T Question

Typically in an exam or problem set we have a problem that's like this: Determine the specified property at the indicated state of water. Locate the state on a sketch of the T-v and P-v diagram. p= 3 ...
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1answer
1k views

Ceramic vase filled with boiling water makes a sound. Why?

I had some old flowers in a vase and noticed the water had become really stagnant, causing the whole room to smell like a fart. So I tipped out the flowers and the old water, and poured some boiling ...
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2answers
393 views

Why does a firebrand glow brightest before it burns out?

I've noticed this in match-sticks, and mango wood. After the flames die out, the brand glows red for a while. The glow is brightest right before it dies out. My guess is that immediately before the ...
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3answers
2k views

How would you store heat?

Um .. naive question perhaps but if somebody wanted to store heat, how would they go about it? Can heat be stored? I'm told that decomposing kitchen waste in a closed vessel results in a rise in ...
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1answer
13k views

Why is my tupperware sealed after heating it up in the microwave?

I had a vegetable soup in a crystal tupperware and I put it in the microwave to heat it up. The funny thing is that when I took it out, it was impossible to open it up. The lid is bent towards the ...
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4answers
44k views

Heat transfer calculated from the specific heat formula

Say I have 10g of silver, whose specific heat is known to be 0.235. I've heated it up from 50.0C to 60.0C. How much heat has been transferred? The equation is: $$ Q = C_pm\Delta t $$ where Cp is ...
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2answers
2k views

Which phenomena is involved in the clothes drying process?

There's this question that has been bugging me most of my life: how is it that wet clothes left hanging to dry, get actually dry? If I get it right, the clothes are a mesh of fibers (we could assume ...
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1answer
3k views

Reversible adiabatic expansion

I am confused with adiabatic expansions. I have a homework problem wherein 2.75 moles of an ideal gas at 375 K expands adiabatically with an initial pressure of 4.75 bar and a final pressure of 1.00 ...
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3answers
301 views

Does entropy measure extractable work?

Entropy has two definitions, which come from two different branches of science: thermodynamics and information theory. Yet, they both are thought to agree. Is it true? Entropy, as seen from ...
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1answer
431 views

$(\mu,P,T)$ pseudo-ensemble: why is it not a proper thermodynamic ensemble?

While teaching statistical mechanics, and describing the common thermodynamic ensembles (microcanonical, canonical, grand canonical), I usually give a line on why there can be no $(\mu, P, T)$ ...
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3answers
4k views

Function of air conditioner

What i always thought that air conditioners blow the cool air without knowing that they actually take the warm air from indoor and from outdoor. But whats the point of taking air from indoor and ...
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1answer
1k views

Heat exchange depending on coolant flow direction

Consider a simplest case of a heat exchanger - two parallel pipes of flowing liquids (say, hot and cold) that have physical contact along some part of their length. Hot water of a certain temperature ...
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4answers
2k views

How do you prove $S=-\sum p\ln p$?

How does one prove the formula for entropy $S=-\sum p\ln p$? Obviously systems on the microscopic level are fully determined by the microscopic equations of motion. So if you want to introduce a law ...
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1answer
933 views

Calculate time to heat my swimming pool

I have a swimming pool of 5300Liters. I have a heating element from a washing machine taking 1min17s to heat a bucket (10L) of water from 22 degrees to 30 degrees celcius. the water in my pool is 19 ...
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4answers
4k views

Heat in the car during sunny day

Why is it hotter inside an isolated car (air conditioning is off) than outside during a sunny day in summer?
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8answers
17k views

Why does the gas get cold when I spray it?

When you spray gas from a compressed spray, the gas gets very cold, even though, the compressed spray is in the room temperature. I think, when it goes from high pressure to lower one, it gets cold, ...
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2answers
9k views

What happens to the absorbed light energy?

When light comes across with a solid material, some of it is reflected, some of it passes through and some of it is absorbed. I understand the reflection and passing through, but I don't understand ...
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2answers
1k views

Is this Landau's other critical phenomena mistake?

There was an old argument by Landau that while the liquid gas transition can have a critical point, the solid-liquid transition cannot. This argument says that the solid breaks translational symmetry, ...
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1answer
675 views

Why is the maximum work achieved in reversible processes?

Let us consider an ideal gas. Let it be present initially in a state $(p_1,v_1,t_1)$. Now let it be driven to another state $(p_2,v_2,t_2)$. Why is it so that during this process the maximum work can ...
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1answer
237 views

Is rocket propellant meaningfully a form of “space junk”

I imagine that most people are familiar with the concept of space junk (or space debris), which is a hazard to space exploration that grows with every item that humans leave in space. Wikipedia lists ...
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How can it be that the beginning universe had a high temperature and a low entropy at the same time?

The Big Bang theory assumes that our universe started from a very/infinitely dense and extremely/infinitely hot state. But on the other side, it is often claimed that our universe must have been ...
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3answers
507 views

Finite difference formulation of the heat equation with thermal conductivity in 1D

This may seem trivial, but I'm having some trouble deriving the finite difference form of the heat equation with a thermal conductivity function $a(x)$ depending on $x$: $$\frac{\partial u(x, ...
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1answer
148 views

SDE for particle, PDE for the density

Given a particle on the plane we can assume that it follows 2D Brownian motion. On the other hand if there is a lot of such a Brownian particles one can be interested in the evolution of the density ...
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1answer
135 views

How does the period of a temperature fluctuation affect the depth to which the ground freezes?

On account of the annual fluctuation of temperature the ground at the town of Ν freezes to a depth of 2 metres. To what depth would it freeze on account of a daily fluctuation of the same amplitude? ...
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1answer
3k views

Why did my liquid soda freeze once I pulled it out of the fridge and opened it?

This isn't a duplicate to "Why did my liquid soda freeze once I pulled it out of the fridge?". My question is why soda froze after it was opened. Opening a can or bottle seems to have a larger effect ...
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2answers
251 views

If I put 3 bottles of water next to each other in the fridge, which one is cold first?

I was wondering: If I put three bottles of water next to each other in the fridge, which one is cold first? Does it matter? Is it the one in the middle because it gets refrigerated by the other two? ...
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5answers
786 views

Should I cook two pieces of Canadian Bacon twice as long as one in a microwave?

It will probably depend on the size of the pieces... but at what point should I stop assuming a linear relationship? I was prompted to ask in a previous question.
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1answer
765 views

Second Law of Black Hole Thermodynamics

I've been looking for a satisfying proof of this, and can't quite find it. I read the brief proof of the black hole area theorem in Wald, which is similar, but doesn't quite come down to the actual ...
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5answers
3k views

Does a full freezer freeze items faster than an empty one?

Let's say we want to freeze a banana. Would it freeze faster if we insert it into an empty freezer, or into one that already contains many frozen bananas?
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4answers
770 views

Will the earth never cool, but only get hotter?

Since the earth is in a vacuum and therefore there is no thermal transfer of heat to anything else, how can it even cool down? It seems like its average temperature would always be constant, ignoring ...
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1answer
278 views

Voltage drop over a cell membrane

Again, a problem from exam preparation: [A] cell's membrane allows sodium ions to pass through it, but not chlorine ions. The cell is placed in a salty solution with a ten times higher ...
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3answers
551 views

Can temperature be defined as propensity to transmit thermal energy?

I was recently surprised to learn that defining temperature isn't easy. For a long time, it was defined operationally: how much does a thermometer expand. Also surprising, temperature isn't a ...
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1answer
561 views

Helmholtz Free Energy relation

Ok so in a lecture my professor gave us this definition: $dF=\left(\frac{\partial F}{\partial T}\right)_{V,N}dT+\left(\frac{\partial F}{\partial V}\right)_{T,N}dV+\left(\frac{\partial F}{\partial ...
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1answer
1k views

Mechanics + Thermodynamics: Bouncing Ball

In preparation for an exam, I'm revisiting old exam questions. This one seems neat, but also quite complicated: A soccer ball with Radius $R=11cm$ is inflated at a pressure of $P =9 \times 10^4 ...
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2answers
7k views

Does tea stay hotter with the milk in it?

A little thought experiment, similar to this one: Imagine you are making a cup of tea when the door bell rings. You've poured the boiling water into a cup with a teabag in it. As you're just about to ...
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2answers
413 views

The entropic cost of tying knots in polymers

Imagine I take a polymer like polyethylene, of length $L$ with some number of Kuhn lengths $N$, and I tie into into a trefoil knot. What is the difference in entropy between this knotted polymer and ...