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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Thermal Conductivity of Metals

My textbook says on conduction: These 'free' electrons can rapidly carry energy from the hotter to the cooler regions of the metal, so metals are generally good conductors of heat. A metal rod at ...
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1answer
47 views

A gas close to zero Kelvin

Consider an adiabatic expansion of an ideal gas that work is done against friction or a piston. Since no heat exchange can occur the gas keep on losing energy and its temperature decreases and the gas ...
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0answers
14 views

Difference between Residual Function and Excess Property

Sengers describes the deviation function as the difference of the actual mixture property and as determined from a model. If this model happens to be the ideal gas model, then it is also called ...
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3answers
127 views

In what limit do we *really* get Maxwell-Boltzmann statistics from Bose-Einstein and Fermi-Dirac?

Fermi-Dirac and Bose-Einstein energy occupation number $n(\epsilon)$ in natural units ($[T]=[\epsilon]$) read $$n(\epsilon) = \frac{D(\epsilon)}{e^{(\epsilon-\mu)/T}\pm 1},$$ where $D(\epsilon)$ is ...
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37 views

Supercritical Steam Expansion [closed]

Ten kg of steam at 500 bar is expanded at constant pressure until its volume increases to seven times its initial value of 0.01 $m^3 $. (a) Calculate the initial and final temperature of the steam ...
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1answer
2k views

Why do I feel cold air in the shower?

Our house has a glass sliding door to the shower. The shower has the dimensions of about 2 feet wide, 5 feet long, and 6 feet high. Above the door (and shower head) there is about 1 foot of open space ...
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1answer
158 views

What's the most fundamental definition of temperature?

What's the most fundamental definition of temperature? Is it the definition concern about average energy, number of micro states, or what? By "fundamental", I mean "to be applied" in such general ...
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1answer
33 views

Does stew lose more liquid if stirred as it cools?

Suppose I cook a stew or soup and then take it off of the stove and leave it uncovered to cool. Of course, it will cool faster if I stir it (more surface area), but it will, eventually, cool to room ...
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1answer
44 views

Power required to keep a freezer at constant temperature

Alright, I'm completely stuck on this and so is everyone else I've asked. A freezer has a temperature Tc = -23℃. The air in the kitchen has a temperature Th = 27℃. The freezer in not perfectly ...
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2k views

Black and white matters. But why and how?

I know black conducts heat while white reflects it. But they are colors after all. If a metal is painted black, it conducts more heat or at a rapid speed than it would do before it was coated. But, ...
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2answers
60 views

Non-additivity of energy (thermodynamics)

In page 15, Chapter 1 (Laws of Thermodynamics) of the book "An Introduction to the Study of Stellar Structure" by Nobel laureate S. Chandrasekhar, it is mentioned (in context of total energy of two ...
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29 views

Specific Internal Energy Decreases with Increasing Pressure?

I was looking at "Properties of Compressed Liquid Water" (Table A-5) in Fundamentals of Engineering Thermodynamics by Moran. Table A-5 shows that the specific internal energy $u$ of compressed liquid ...
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64 views

Invariance of Temperature in Classical Physics

How can we explain that Temperature is a classically frame-independent quantity to high school kids?
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3answers
362 views
+50

Hot water freezing faster than cold water

This question has puzzled me for a long time. There is already a question like this on Physics.SE. John's answer to the question seems quite satisfying. But when I googled the cause I found this and ...
2
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1answer
67 views

How can such a wave exist at the surface of the sun?

Recently, I came across the following picture from NASA's SOHO observatory: It seems evident that this is a transverse wave (mind the ring which is bright and dark). But how can this be the case ...
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1answer
73 views

Why don't bubble lights explode?

As a child, I loved to watch the bubble lights at Christmas time. The colorful bubbling was hypnotic. However, there was always something about them that bothered me. With all of that boiling ...
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0answers
18 views

Distribution of temperature in a plume of a jet

The exaust gases of a plume of a missile have a distribution in temperature and in density vs. distance from the nozzle. Using a CFD software it is quite simple to get such distribution. Is there some ...
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0answers
40 views

What to do when you are living in very cold environment? [closed]

I am on my way to a shimla, and as it is one of the coldest places of India. Previously I lived in a warm environment of southern india. What would be the correct way to live in a cold environment? I ...
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1answer
69 views

Whenever we fill a bottle with cold water and close it, why is it that after a few seconds we notice cold water droplets outside the bottle?

Whenever we fill a bottle with cold water and place back the cap tightly closing it, why is it that after a few seconds we notice cold water droplets outside the bottle as if the water is coming out ...
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1answer
25 views

what property of steam makes it the preferable motive fluid in jet ejectors? why not air or nitrogen?

I want to know what properties of steam make it the fluid of choice in steam turbines jet ejectors. I want to understand the mechanism of energy conversion in these equipment and hence understand ...
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1answer
53 views

Lev Landau's proof of molecular motion at absolute zero?

I am reading the book "The man they wouldn't let die" by Alexander Dorozynski, which is an biography of Russian theoretical physicist Lev Landau, and I have encountered this passage Absolute zero ...
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1answer
51 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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2answers
1k views

Why isn't water running faster hotter?

I was running the washing up water this morning, and started to think about why the cold tap isn't hot, and why the water doesn't get hotter the faster it is flowing (if anything, the cold tap gets ...
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2answers
53 views

Electromagnetic radiation and health issue

A lots of article even wiki tells that Cell phone radiation is very dangerous for health. Some people tell that it can be reason for brain cancer. A article Mobile phone subsides man’s sperms! ...
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2answers
51 views

Measurement of heat in electrons

Is there any method to measure the heat of an electron and if there is; then is it a constant or a variable.
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2answers
58 views

Can we apply $pV^\gamma$=const only for quasistatic adiabatic process?

But If this is so, I have often seen people applying this formula for quick processes where no heat exchange is possible. Here is an example from where I am quoting the following: we will assume ...
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1answer
16 views

Is heat added to an air bubble rising in water?

An air bubble was initially released from the bottom of an ocean. Assume that the air in the air bubble is an ideal gas and its temperature remains constant at 25 degrees Celsius. Is heat added or ...
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1answer
27 views

Spherical Shaped Electrical Leads for Thermal Conductivity Mitigation?

I am designing a thermionic converter and one of the biggest inefficiencies is the thermal conductivity and limited electrical conductivity of the leads. I'm trying to mitigate the loss of heat ...
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0answers
74 views

Why did everything in space cooled out?

Through my research, I learned that; According to thermophysics, heat always moves from and area of high heat to an area of low heat. Space has no heat at all. It is extremely cold However, ...
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1answer
24 views

Why is the outside run of high presure line on a ductless mini-split airconditioner insulated?

On every ductless mini-split air conditioner I've ever seen, both the high and low pressure lines are insulated between the compressor and the building. It seems like the liquid refrigerant coming ...
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1answer
34 views

Vapor-compression refrigeration

In a vapor-compression refrigeration system I would like to understand the following : Why is there a need for the compressor ? Can't the saturated vapor from the evaporator be cooled directly in ...
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2answers
32 views

What caused a fluctuating cloud to form in a jet engine intake on a humid day?

I was on a commercial flight in a 737 stationary at idle on a taxiway. It had recently stopped raining so the relative humidity was likely near 100% and the air temperature was about "light jacket" ...
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1answer
73 views

Units kT = 1… why?

Why is it convenient to choose units kT=1? It came up in this paper: http://jfi.uchicago.edu/~leop/SciencePapers/scaling%20and%20universality%20in%20statistical%20physics.pdf in page 4, equation ...
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1answer
60 views

Can you extract energy from “hot” things without a temperature differential?

I've been reading about extracting energy from heat, particularly Sterling engines. There's always a temperature gradient. Heat flows from the hot side to the cold side through the working fluid. As ...
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1answer
17 views

Perfect Ideal Gas Modelization of Air

I'm solving a Thermodynamic problem. I have Air at temperature of 293.15 K, and pressure of 20 MPa. I would understand if is possible to consider this an Ideal Gas or not (and if is possible which are ...
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5answers
3k views

How badly could someone be injured by concentrated sunlight?

Recently-ish, I stumbled across an interesting short story (by way of Science Fiction & Fantasy Stack Exchange) where a soccer referee is apparently incinerated by concentrated sunlight. Where ...
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1answer
40 views

How much electricity could be generated by cloths made of thermocouples?

Lets say that we made a glove, shirt, pants and a hat out of the most effective thermocouple material available today. How much electricity would be generated by each, by a healthy person, on a cool ...
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3answers
2k views

What is the minimum pressure of a medium for which a sound wave can exist?

At what pressure will be particles in a medium be unable to form a sound wave when disturbed? How can this pressure be described mathematically? My guess is that this would correspond to the point at ...
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0answers
38 views

Free energy a continuous function of temperature but may not be differentiable everywhere?

So according to my understanding, the free energy of the system should be a continuous function of temperature. This is because if the free energy is not continuous at temperature T, then at this ...
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5answers
615 views

Why can't a gas be liquified by pressure above its critical temperature?

What is the cause behind a gas being difficult to liquify above its critical temperature no matter how much pressure is applied on it?
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1answer
42 views

Are all means of heating equally efficient? [duplicate]

In terms of cost of electricity, does it matter if I heat my room using a space heater, an open oven, a flood light, an ASIC? Assume no energy escapes the room, that the heat quickly becomes uniformly ...
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1answer
45 views

is boiling of water an isobaric process?

Is the conversion of water into steam at 100°C an isobaric process? It is an isothermal process, but does pressure rain constant during this process?Please explain as well..
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1answer
70 views

Boiling Pasta resulting in a Torus like shape?

I noticed when I was boiling pasta the other day that the pasta uniformly spread out and formed a donut like torus. Why does this happen? Does it have to do with the shape of the pot? I tried to take ...
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1answer
60 views

Why are ceramic containers used for hot beverages?

Why are ceramic containers used for hot beverages? For example, is it dangerous to use plastic? Are there any other reasons other than to protect hands from heat?
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1answer
31 views

What does adding a visible light blocking IR filter do with heat?

Lets say I have a strong halogen light source which has a lot of IR radiation (e.g. a construction lamp). If I change the transparent front glass from the enclosure with a IR filter that blocks ...
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0answers
27 views

Cost vs. purity producing liquid oxygen [closed]

We are a group of rocket amatures who build rockets using LOX and ethanol as propellent. We normally buy the LOX from supplier. But lately we have been discussing if there is an easy way to produce it ...
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1answer
17 views

Efficiency of a thermal reactor

I was told that the efficiency of any thermal reactor increases if it is operated at higher temperature- in this case, nuclear reactor was referred to. But I cannot seem to understand why...
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4answers
4k views

Why does cold metal seem colder than cold air?

(I apologize for this elementary question. I don't know much about physics.) Let's say that I put a metal pot in the refrigerator for several hours. At this point, I guess, the pot and the air (in ...
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1answer
67 views

Why does water freeze from top to bottom

I was wondering why water freezes from up to bottom and not the other way around. The reason I question this is because in a Video I came across, I discovered water freezes from top but surely with ...
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0answers
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Building free energy directly from Lagrangian

Energy can be built from Lagrangian when considering the symmetry of time $(\frac{\partial L}{\partial t}=0)$. Free energy is a generalization of energy when the system exchanges heat with the ...