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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34 views

Do air particles always rush to fill a container? [closed]

I'm sitting here in the metro station, drinking a bottle of water, and watching how the flow of water out of my mouth changes as air rushes into the bottle. My questions is: in space, obviously the ...
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1answer
31 views

As hot air rises is the cold air that rushes in pushed in or sucked in?

I seem to remember from high school, the state of equilibrium. Volumes of more molecules wanting to get to a volume of less molecules and causing a state of equilibrium. From this I believe cold air ...
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0answers
22 views

Heating of mixture of gases with one gas barely above its boiling point

What happens when mixture of two gases is heated in a closed container? If one gas expands faster than the other and increases pressure of the container enough so that the boiling point of the other ...
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3answers
27 views

Heat transfer equally distributed?

When heat is introduced to a copper bar's end surfaces(right or left surface) of a certain volume $cm^3$, is the heat uniformly distributed? In my calculations of heat transfer, I'm using $$Q = mC_P \...
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2answers
55 views

Carnot engine basics?

A line in my textbook says.. ' if we employ any other process that is not adiabatic, say an isochoric process, to take the system from one temperature to another, we shall need a series of ...
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1answer
35 views

Effectiveness of phase-change materials vs water for heat storage?

I'm trying to understand the benefit of specialized phase-change materials vs. water for absorbing heat in a home during the day. It's my understanding that selecting phase-change materials whose ...
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1answer
25 views

Flame composition types

Can anyone define the atomic structure of a carbon fuelled flame. I have studied variations of flame patterns but this type seems to stand out.
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5answers
332 views

Thermodynamic equilibrium - will the piston move?

Friend asked me this question and I didn't manage to solve it with basic thermodynamic reasoning. I believe this problem is easly solvable via numeric methods by choosing specific systems, though I ...
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1answer
25 views

Coupling constant for an object in a photon gas

I want to model a photon gas as a bath of harmonic oscillators, and examine the effects of this bath on a system which is also a harmonic oscillator. The trouble I'm having is in relating the ...
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5answers
7k views

Why is Helium so hard to liquify?

By the end of the 19th century all gasses had been liquefied apart from helium (He). What is it about helium that makes it so hard to liquefy compared to the other gases? And why does it need to be ...
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1answer
30 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
101 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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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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0answers
53 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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1answer
67 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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3answers
654 views

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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2answers
185 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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2answers
69 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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2answers
65 views

Blocks releasing heat energy [closed]

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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2answers
184 views

How do we explain the existence of liquids, from a mathematical or computational perspective? [closed]

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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1answer
32 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
55 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
102 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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1answer
25 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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7k 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
84 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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4answers
65 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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0answers
81 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
24 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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3answers
42 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
251 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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1answer
51 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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2answers
97 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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2answers
82 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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2answers
50 views

Radiative Cooling of metal object

We have this experiment where a metal bar is heated and then we have to make a model for the cooling that occurs. We get numbers for how long it takes the metal bar to cool from 200 to 100 degrees ...
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0answers
56 views

Hindered rotation model for flexible polymers: deriving the Flory characteristic ratio

In the hindered rotation model we assumes constant bond angles $\theta$ and lengths $\ell$, with torsion angles between adjacent monomers being hindered by a potential $U(\phi_i)$. In Rubinstein's ...
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1answer
68 views

Does the temperature of a body depend on the frame of reference? [duplicate]

Does the temperature of a body depend on the frame of reference?
1
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1answer
82 views

Is it possible to have light without heat? [duplicate]

I am trying to think of a light source that doesn't generate heat; but I am not sure if such a phenomenon exists. I am not referring to passive light (such as reflected light, ie, moonlight) but an ...
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2answers
60 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 ...
4
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1answer
90 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
17 views

Lengthening in-flight evaporation time of water droplet in air

How one can increase the in-flight evaporation time of sprayed water droplets in air without changing the thermodynamic conditions of the ambient air ( i.e. RH, T ). For instance mixing water with ...
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0answers
30 views

A micro-reversible stochastic process that models transitions between states with variable energies

Suppose we have a system with 3 possible states A, B and C (there could be $n$ states as well) with energies $E_a(t)$, $E_b(t)$ and $E_c(t)$ that vary with time. If our system has a constant finite ...
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2answers
37 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: $$P'(...
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1answer
29 views

Example of a Carnot machine made of a different physical system than a ideal gas?

Anybody knows an example of a Carnot machine made with any different thing than a gas? For example wire or a magnet. I was wondering that since I read the Kardar's book on Statistical Mechanics. He ...
2
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1answer
95 views

Cooling of a hot metal object in air

We have this experiment where a metal bar is heated and then we have to make a model for the cooling that occurs. We get numbers for how long it takes the metal bar to cool from 200 to 100 degrees ...
0
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1answer
105 views

Finite Difference Method (FDM) solution to heat equation in material having two different conductivity

I am not from a mechanical engineering background and I have not taken any courses in PDE so this may seem trivial for many. and I am writing a Matlab code with the objective to solve for the ...
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1answer
16 views

Relate conductor current with temperature

I'm working with heating wires and I wan't to probe that for a wire with a constant radio it's only needed to know the current to estimate the temperature. Can I just say that if for a given current ...
2
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0answers
17 views

Fermi-Pasta-Ulam for the beam equation

The Fermi-Pasta-Ulam numerical experiment is based upon the discrete wave equation, with a small non-linearity added to the forcing term. Does anybody know of similar research performed on the beam ...
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0answers
25 views

Time to recover to ambient temperature from a cold condition

How to find the time taken by an object ( Made of say Aluminium) weighing about 1 Kg initially at a low temperature ( say -40 degree C) to regain temperature to ambient levels ( say + 30 Degree C) ...
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1answer
35 views

Adiabatic compression for an ideal gas

I´m trying to solve the exercise 7.4-11 of Callen Thermodynamics 2nd edition. Where a 2-mole ideal gas of pressure $10^5$ Pa and temperature of $273.15$ K (0° C) is adiabatically compressed to $573.15$...