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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What to do when you are sitting in a closed room without any fan or AC

I suffered this today, when the solar panels of our college stopped to work. Imagine a situation in which you are sitting in a botany lecture conducted by a 73 year old man, who cannot speak loud and ...
2
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0answers
55 views

Why is thermodynamic equilibrium not reached by the system during a thermodynamic irreversible process?

In reversible process,due to infinitesimal steps,the system remains in thermal equilibrium(why?) . But in irreversible process, thermal equilibrium does not exist. What is the cause for this ...
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2answers
43 views

Liquid Nitrogen Expansion to Desired Temperature

I want to take liquid nitrogen in a pressurized container and spray it through a hose onto objects in a room. The container has a pressure regulator so I can adjust pressure as desired. The ...
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4answers
85 views

Entropy and dark matter structure

Inspired by this question. I believe that the usual explanation that preserves the second law of thermodynamics as an astrophysical gas cloud collapses under gravity is that the gas must heat and ...
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1answer
74 views

Why does the majority of smoke leave when flames appear?

When I burn wood, paper, or other plant matter, where there is a flame, there generally isn't too much smoke, but it I blow the fire out, smoke starts billowing up. It billows thicker and thicker as ...
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3answers
83 views

Are galaxies, stars, planets, and ultimately life in violation of the second law of thermodynamics? [duplicate]

How can we think about entropy in these situations? To my knowledge all of these structures are born out of gravitational interaction. However, it would seem that the formation of these more organized ...
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0answers
36 views

Heat transfer to a cube from one of the faces [closed]

Heat Flux= 10 MW Inlet water temperature = 28 degree centigrade for cooling purpose through a tube passing through the centre of retangular block of length 50 mm,height 30 mm and width 30 mm inner ...
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8answers
1k views

What is entropy really?

On this site, change in entropy is defined as the amount of energy dispersed divided by the absolute temperature. But I want to know: What is the definition of entropy? Here, entropy is defined as ...
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2answers
59 views

What is entropy of the universe? [duplicate]

What is entropy of the universe? What is the change in entropy of our universe? Is this change increases or decreases? If the entropy of universe keeps on increasing then what are the consequences? Is ...
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57 views

Milk-First School

I have always been struck by the huge amount of different arguments about the issue: When you make a cup of tea, the milk should be poured first or added to the cup after the tea? Wikipedia, ...
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3answers
384 views

Is speed an intensive property?

I remember being taught in elementary physics that while it makes sense to add volumes, masses, or heat, it makes no sense to add temperatures. As I wanted to use that to illustate some other issue, ...
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2answers
167 views

Thermal superconductivity

I have heard several times of the concept of "thermal superconductivity" (As opposed to "electrical superconductivity"), but I am unclear on exactly what that could mean. It turns out to be really ...
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2answers
54 views

Is enthalpy also valid for liquids and solids?

The definition of enthalpy is $$H=E+PV,$$ is it only valid for (ideal) gas? As this naturally comes from the first law of thermodynamics, $$dE=dQ+PdV$$ for a enclosed system of gas. Can we talk ...
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1answer
25 views

can I tune a magnetic field to conduct heat from a rotating object?

Is there a way to transfer heat from a rotating object made of iron into a suitable heat sink using a magnetic field as a transfer medium?
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1answer
91 views

Why does the thermal conductivity of water decrease with increasing salinity?

Intuitively I would expect the thermal and electric conductivity to be positively related, and since electric conductivity increases with salinity, so should thermal. But according to this table ...
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1answer
61 views

Relationship between temperature and energy

What is the definition of temperature in relation to energy? I'm mostly interested in general dimensional terms. Is temperature the kinetic energy per mass? Or kinetic energy per volume?
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2answers
68 views

What's the difference between energy and temperature in field theory?

I'm familiar with the formalisms for both zero temperature and finite temperature field theory, but (somewhat embarrassingly) I don't actually have a good physical intuition for when physical ...
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3answers
739 views

Didn't we mess up with the temperature?

The following passage has been extracted from the book "The Feynman Lectures on Physics-Vol l": The mean kinetic energy is a property only of the "temperature." Being a property of the ...
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1answer
32 views

How to transfer propane from a SMALL cylinder to a SMALL metal cylinder [closed]

I made a metal cylinder that is the SAME size as my 400g propane cylinder (picture: here). I want to transfer ALL (or almost all) of the propane from the propane cylinder to my metal cylinder, ...
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2answers
284 views

How can it be that the sun emits more than a black body?

As far as I know, a black body is an ideal emitter. So how can it be that a non-ideal emitter emits more radiation than a black body? This happens only in a very limited area at around 500nm, but it ...
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2answers
73 views

Relations between pressure and temperature

I have several questions concerning thermodynamics and I order them in 4 points that may be related: What's the difference between heat and work at the atomic level? Isn't heat simply work between ...
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2answers
40 views

What materials are used in non thermal plasma?

While reading about non-thermal plasmas, I came across their ionization potentials(~1%), and other capabilities, such as their non Maxwellian energy distributions. At what temperatures, and pressures ...
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1answer
58 views

How much work will a human do to lift a weight?

I saw a pretty simple homework question here that asked how much work it takes to lift a 200 kg weight, and while the math for a basic answer is simple the weightlifter in me instead wanted to ...
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2answers
54 views

What happens at the subatomic level when energy is added to an atom?

For the sake of simplicity I shall use the hydrogen atom. I know that adding energy to the hydrogen atom means bombarding it with photons. I am curious about what happens to the quarks and electron of ...
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4answers
88 views

The conduction electrons in metals is a thermal phenomenon?

When applying an external electric field in a metal at absolute zero, there is electrical current? There must be thermal fluctuations in the electron's band to be occurs current?
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1answer
97 views

Entropy of a two-level system

Consider a two-level system with energies and degeneracies $\epsilon_0 = 0, g_0=1$ and $\epsilon_1 = \epsilon, g_1=4$. I can show that the temperature at which both levels are equally populated is ...
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1answer
32 views

minimum possible absolute temperature in the universe? [duplicate]

Sorry guys i went wrong in my previous question , actually my question is what is the minimum possible absolute temperature in the universe of what ever substance...?
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0answers
26 views

Is It Possible To Have Temperature Below Absolute Scale? [duplicate]

Guys I have a doubt Is it possible to maintain the temperature of any Substance Below the Absolute Scale?
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30 views

White bread toasted seems hotter than brown bread?

Ok this is a bit of a random question but I 99% of the time use white bread for toast and I always toast my bread the same amount and every time I take it out it's too hot to handle and the butter ...
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2answers
129 views

Why does the second law of thermodynmics only occur in the time dimension?

If I break an egg, how broken it is depends on "when" I am not "where" I am. Why is the time dimension special?
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1answer
74 views

Heating up a room to 50 °C

Suppose I have an empty room of $24 m^3$ and I want to heat it to 50 °C, assuming the current room is well isolated and the current temperature is 20 °C. How much power (in Watts) would a single ...
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3answers
135 views

Why doesn't Euler's theorem provide an *absolute* energy scale

we know that for a one component system $$U= TS - PV + N \mu$$ Now all terms on the right hand side have well defined zeros, but the internal energy is known to be a relative quantity, with no ...
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2answers
100 views

How can heat turn into light

I am confused about how hot surfaces can radiate light to their surroundings. When I shine a light on a surface the light turns to heat spontaneously, and when I leave that hot surface it radiates ...
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1answer
33 views

Does the energy required to increase a volume of water's temperature increase as that temperature increases?

Obviously in a simple, classroom style experiment the energy required to increase water temperature is a constant and thus wouldn't change, but what if we made the experiment just slightly more real ...
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2answers
107 views

Are isobaric, isochoric, and isothermal processes quasistatic by definition?

Let us start from definitions, as they are given in many sources. A quasistatic process is an idealized processes that happen out so slowly that a system go through a sequence of states arbitrarily ...
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2answers
121 views

What if an asteroid the size of the moon hitting earth

Would we all parish due to excessive heat? Or would that be only limited to the area near the impact while as the people on rest of the earth would die from other phenomenons such as mega earthquakes, ...
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94 views

What are the implications for the AdS/Cft program if AdS is unstable?

To my understanding recent progress in the study of the non linear stability of AdS spacetime suggest that $AdS$ might be unstable. If this is true, what are the physical and mathematical ...
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1answer
25 views

Does it take a lot of energy to heat metals up?

Why does it take a lot of energy to heat metals? And to do it quicker it requires much more energy? What about the use of lasers would that be an efficient process that is quicker and requires less?
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1answer
68 views

When Fire meets Water

To preface, I am not a scientific mind, but a writer looking for some validity to a possible scene. That being said, please forgive me! In my scene, huge masses of fire are raining from the sky and ...
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0answers
53 views

What algorithms can be used to compute the binodal in a ternary Flory-Huggins theory?

What are the most popular algorithms used to obtain a binodal curve for the ternary mixture (starting from Flory-Huggins theory)? I would like to obtain a plot similar to the one calculated here ...
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1answer
50 views

How can momentum changes from individual collisions be considered as a whole?

I have a question about deriving the equation of kinetic theory of ideal gas $$PV=\frac{1}{3} Nmc_r^2$$ where $N$ is number of atoms, $c_r$ is root mean square of atom speed and $m$ is mass of one ...
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1answer
48 views

Efficiency of reversible engines

I'm a little confused about something. All reversible engines have the same efficiency, or one could drive the other to move more heat in the reverse direction. Also, no engine has an efficiency ...
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1answer
39 views

How to define the thermodynamic temperature

I've been reading derivations of the thermodynamic temperature scale. I'm assuming these are using Kelvin's method. I follow the math and the conclusion of the argument, but I don't understand how it ...
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1answer
314 views

Why does earth cool? [duplicate]

This question is boggling me for some time. We know that heat can be transferred from matter to matter and heat is nothing more than tiny atoms vibration intensity (correct me if I'm wrong). But space ...
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0answers
36 views

Steam Turbine Inlet Velocity

Consider an ideal steam turbine. The power generated by a steam turbine comes down to the torque and the angular velocity, which is ultimately dependent on the velocity at which the flow enters the ...
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2answers
942 views

Temperature of a neutron star

In our everyday experience termperature is due to the motion of atoms, molecules, etc. A neutron star, where protons and electrons are fused together to form neutrons, is nothing but a huge nucleus ...
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0answers
47 views

Is the second law of thermodynamics a real law? [duplicate]

Everytime I ask people why the second law of thermodynamics is true, they say because the probability of entropy increasing is very large. This for some reason doesn't seem right for me. Just because ...
3
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2answers
52 views

Why doesn't water in water barometer boil?

I have read that the pressure in a water barometer at the top of the water column is around 0.5 psi and at such low pressures water should boil at around ~26°C (Room temperature). [1] [2] How ...
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1answer
26 views

Chemical potentials for multicomponent solids

I have a problem understanding how to deal with the chemical potential when two thermodynamic systems are in contact. For simplicity, let us consider $T=0\ K$. We have a system that is composed of two ...
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1answer
40 views

Which function denotes the energy of thermal motion within a system?

In thermodynamics, the heat $Q$ is defined as a type of energy in transfer, and is not a state function, which function denotes the energy of thermal motion within a system? 1) $TS$, (there is a ...