Questions tagged [thermodynamics]
Covers the study of (mostly homogeneous) macroscopic systems from a heat/energy/entropy point of view. Consider also using tag: [statistical-mechanics].
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Does hot air really rise?
"Heat rises" or "warm air rises" is a widely used phrase (and widely accepted phenomenon).
Does hot air really rise? Or is it simply displaced by colder (denser) air pulled down by gravity?
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How do whisky stones keep your drink cold?
From a discussion in the DMZ (security stack exchange's chat room - a place where food and drink are important topics) we began to question the difference between how ice and whisky stones work to ...
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Why is the Sun approximated as a black body at ~ 5800 K?
Apparently spectral solar radiation is approximated by a black body at 5800 K. The spectral black body distribution (Planck distribution) is shown below (from Incropera, Fundamentals of Heat and Mass ...
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Why does it take so long for a gas to reach a thermal equilibrium?
Imagine a 1m cube of air in an insulated container, where you have heated the air in one half but not in the other. Intuitively, given molecules are moving so fast, you would expect the energetic ...
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What is cold wind?
As per my understanding, temperature is the movement of particles in an environment. A highly energetic environment where particles possess high energy has a high temperature,
and low energy means low ...
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Why can some electromagnetic waves heat things up while others cannot?
I have read that heat radiation happens in the form of infrared, which is an EM radiation with a longer wavelength than visible light. So the heat radiation that you can feel in an oven or under the ...
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Why doesn't the entropy increase when two similar gases mix with each other?
Entropy increases when two substances mix with each other.
For example, the entropy of mixing of two different gases are given by $$\Delta S= 2Nk\ln\frac{V_f}{V_i}\;.$$
But, the entropy doesn't ...
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Are specific heat and thermal conductivity related?
Are there any logical relationship between specific heat capacity and thermal conductivity ?
I was wondering about this when I was reading an article on whether to choose cast iron or aluminium ...
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Can we cool Earth by shooting powerful lasers into space? [closed]
In a sense, the climate change discussion revolves around the unwanted warming of the earth's atmosphere as a whole.
It seems a bit too obvious to be true, but could we cool the atmosphere by simply ...
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References about rigorous thermodynamics
Can you suggest some references for rigorous treatment of thermodynamics? I want things like reversibility, equilibrium to be clearly defined in terms of the basic assumptions of the framework.
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Why is snow white when water has no color? [duplicate]
I just don't get it. Isn't snow just another form of water? Also are all ices transparent or do they go white after a certain temperature?
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Why do things cool down?
What I've heard from books and other materials is that heat is nothing but the sum of the movement of molecules. So, as you all know, one common myth breaker was "Unlike in movies, you don't get ...
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According to the inverse square law, is the intensity at the source always infinity?
I'm trying to design a script for a Unity game that can accurately (give or take) simulate heat based on distance from a source. Using the inverse square law seems to be a way I can do this, but ...
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Why are expressions such as $\operatorname{ln}T$ used in thermodynamics where $T$ is not dimensionless?
In all thermodynamics texts that I have seen, expressions such as $\operatorname{ln}T$ and $\operatorname{ln}S$ are used, where $T$ is temperature and $S$ is entropy, and also with other thermodynamic ...
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Why does the nature always prefer low energy and maximum entropy?
Why does the nature always prefer low energy and maximum entropy?
I've just learned electrostatics and I still have no idea why like charges repel each other.
http://in.answers.yahoo.com/question/...
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Why is it so much more energy intensive to compress hydrogen than methane?
Why do you need 13.8 MJ/kg (9% of energy content) to compress hydrogen to 200 bar, but only 1.4 MJ/kg (2.5% of energy content) for methane?
I looked into compressibility factors and the ...
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Why does maximal entropy imply equilibrium?
From a purely thermodynamical point of view, why does that entropy have to be a maximum at equilibrium? Say there is equilibrium, i.e. no net heat flow, why can the entropy not be sitting at a non-...
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Why does time not run backwards inside a refrigerator?
The arrow of time is often associated with the fact that entropy always increases. On the other side that should mean, if entropy decreases time should run backwards. But inside a refrigerator we have ...
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Dependence of spin on classical vs non-classical physics?
Textbook derivations often state that spin can be derived by adding relativity to quantum mechanics. The general argument comes in several steps :
Schrödinger first tried to describe quantum ...
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How do you prove the second law of thermodynamics from statistical mechanics?
How do you prove the second law of thermodynamics from statistical mechanics? To prove entropy will only increase with time? How to prove? Please guide.
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If you were invisible, would you also be cold? [closed]
If you were invisible, would you also be cold? (Since light passes through you, so should thermal radiation.)
Additionally, I'd like to know if you were wearing invisible clothes, would they keep you ...
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Why does holding a hot object with a cloth make it feel less hot?
Let's say that I held a hot object with a warm cloth. It instantly feels less hot and only warm to the touch. This is because the cloth is an insulator and doesn't allow as large a heat transfer as if ...
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Difference between heat capacity and entropy?
Heat capacity $C$ of an object is the proportionality constant between the heat $Q$ that the object absorbs or loses & the resulting temperature change $\delta T$ of the object. Entropy change is ...
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Why do ice crystals form from the top to the bottom of a bottle filled with supercooled water?
If I bang a bottle filled with supercooled water against a hard surface, the ice crystals form from the top to the bottom:$\hspace{50px}$$\hspace{75px}$–source.
YouTube has videos showing this ...
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Thermodynamic equilibrium - will the piston move?
Friend asked me this question and I didn't manage to solve it with basic thermodynamic reasoning. I believe this problem is easly solvable via numeric methods by choosing specific systems, though I ...
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Why does the Boltzmann factor $e^{-E/kT}$ seem to imply that lower energies are more likely?
I'm looking for an intuitive understanding of the factor $$e^{-E/kT}$$ so often discussed. If we interpret this as a kind of probability distribution of phase space, so that $$\rho(E) = \frac{e^{-E/kT}...
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How does the Eco-Cooler air conditioner really work?
This article describes a device for developing countries which apparently cools the air by 5 °C without electricity. According to its YouTube video, it works by lowering the pressure to drag in the ...
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Why does a room not warm up faster when I put the heater's thermostat on a higher value?
I would say it should warm up faster because the difference in temperature between the room and heater is higher.
Edit: I am talking about a convection heater.
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Why is the second law of thermodynamics not symmetric with respect to time reversal?
The question might have some misconceptions/ sloppy intuition sorry if that's the case (I'm not a physicist).
I seem to have the intuition that given a system of $N$ charged particles in 3D space ...
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Why doesn't my kitchen clock violate thermodynamics?
My kitchen clock has a pendulum, which is just for decoration and is not powering the clock. The pendulum's arm has a magnet that is repelled by a second magnet that is fixed to the clocks body. The ...
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Will drinking ice cold water and eating cold food cause weight loss (over a period of time)? [closed]
A friend of mine has the idea that drinking cold water and eating cold food will assist them in losing weight.
The core temperature of a human body is 37$^{\circ}$ C.
If they drink water, at a ...
user81619
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How do scientists know the min limit of temperature is -273 degree celsius?
How do scientists know the min limit of temperature is -273 degree celsius?
I wonder how do scientists confirmed that there is no place belong to less than -273 degree celsius in the universe? Why the ...
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Why does heat added to a system at a lower temperature cause higher entropy increase?
Entropy is defined in my book as $\Delta\ S = \frac{Q}{T}$. To derive the formula it says that entropy should be directly proportional to the heat energy as with more energy the particles would be ...
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Explanation for negative specific heat capacities in stars?
I've just found out that a negative specific heat capacity is possible. But I have been trying to find an explanation for this with no success.
Negative heat capacity would mean that when a system ...
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Is there a quasistatic process that is not reversible?
I have seen several questions and good answers on the link between reversible and quasistatic processes, such as here or here. However, these questions only adress one side of the problem : a ...
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Why can the entropy of an isolated system increase?
From the second law of thermodynamics:
The second law of thermodynamics states that the entropy of an
isolated system never decreases, because isolated systems always
evolve toward ...
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Is frequent opening of the fridge really so significant for the power consumption?
I've read several popular articles telling that frequent opening of the fridge highly increases the power consumption.
Is it really so significant? Isn't the heat in the room-temperature food which ...
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Can I take heat from the air and convert it to electricity?
Its a summer day and the air in my house has been heated up. I could switch on my air conditioning, but then I'd be using energy from the grid in order to reduce the amount of energy in my house.
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Can a single classical particle have any entropy?
recently I have had some exchanges with @Marek regarding entropy of a single classical particle.
I always believed that to define entropy one must have some distribution. In Quantum theory, a single ...
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Why aren't gas planets and stars fuzzy? [duplicate]
The edge of Jupiter looks very sharp.
Even more bothersome, the edge of the sun looks sharp, aside from kind of a soup of particles floating above it.
The sun's surface has an incredibly low density....
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Melted chocolate forming fractal branches
Tree-like structure in chocolate
Today I let some melted chocolate solidify in a smooth bowl in my fridge. When it had settled, I gently heated the outside of the bowl with warm water to unstick the ...
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Is concept of entropy really indispensable? Especially when the concept of potential energy can serve the purpose?
We see that all the natural systems aspire for minimum potential energy state and we also see that all the natural systems also aspire for maximum entropy state. Now from this understanding it seems ...
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Does wrapping a wet paper towel around a glass bottle really speed up the cooling process?
There are claims like this one that you can improve the cooling speed of beverages when you put them wrapped in a wet paper towel inside the refrigerator/freezer.
I've just tried it by myself and it ...
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Why does the vapour bubble in an inkjet printhead collapse so fast?
I am studying the inkjet printer in detail. I have come across thermal inkjet printing technology (bubble inkjet technology) and this short discussion below.
We create a water vapour bubble by heating ...
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How to calculate how many photons are in the universe?
The "universe" is a sphere with a radius of $10^{25}$ m
the medium temperature is 3K,
how many photons there are in the universe?
$$n_\gamma = \int_{0}^{\infty} \frac{8h\pi\nu^3} {{c^3}{}} \...
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Could you please give an intuitive definition of chemical potential?
Could you please give an intuitive definition of chemical potential? It seems that it is an extremely important notion of physics but definitions are really vague.
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Why don't Wien displacement law curves cross?
In the above image, the curves for different temperature dont intersect anywhere. Stefan-Boltzmann law and Wien displacement law dont preclude the intersection.
Is it because if, for example, they ...
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How can entropy increase in quantum mechanics?
Lets say we have a closed system with states in a Hilbert space $\mathcal{H}$. Every state can be expressed as a sum of energy eigenstates. In a closed system, like a box of atoms, entropy will ...
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