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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How can Maxwell's Demon erase information while a black hole can not?

It is stated, that information can't disappear even in black holes. On the other hand, it is stated, that mystic beings, like Maxwell demons, can easily erase any information if they just pay with ...
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1answer
61 views

Can I manually speed up convection?

Let's say, I have half bucket of boiling water and I have added equal amount of freeze cold water to it. I want to have equilibrium temperature reached as quick as possible. Can I speed up the ...
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76 views

How can there be any probability of finding the molecules clustered in half of the box,the other being empty?

Suppose,there are six molecules(indistinguishable) constantly jostling around in a box. The central configuration is when there are $3$ molecules in either halves of the box and having probability ...
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4answers
72 views

Does it matter which blanket I take below and which one above when I cover myself with the two? [closed]

If I take two different blankets to cover myself, does it matter which one I take below and which one above? Will both the arrangements give me the same comfort or one of them will give me better ...
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75 views

If the specific heat capacity depend upon the temperature, what formula we should use instead of $Q=mc\Delta T$

Recently, I learned that specific heat capacity is not constant in different temperatures and it depends on the temperature.If I have diagram like this (consider that the red part is a quarter of ...
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95 views

Why is there a limited range of possible soap bubble size?

Soap bubbles are never "too small" or "too large". What defines the range of possible diameters of a soap bubble? Related questions: Why do steam bubbles increase in size as they rise, Why is the ...
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1k views

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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1k views

Is carbon dioxide a greenhouse gas? [duplicate]

Possible Duplicate: What experiments prove the greenhouse effect? I am seeking for a proof that CO2 is a greenhouse gas. I posted this on Skeptic.SE recently but found no help in seeking ...
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106 views

Is my conceptual understanding pertaining to heat & temperature correct?

From what I've understood: Heat is the total sum of kinetic energy translational energy possessed by individual atoms in an object. Temperature is the average kinetic energy translational energy ...
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62 views

What is dynamic equilibrium actually?

Recently I have asked question sort of like that: Is thermodynamic equilibrium static or dynamic ? But then I wanted to realize what actually a dynamic equilibrium is. I read the wiki article, ...
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142 views

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 ...
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79 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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100 views

Is it possible to have $\Delta T\neq 0$ with no heat exchange $Q=0$, no work $W=0$ done, and no change in internal energy $\Delta E=0$?

Is it possible to have $Q=0$, $\Delta E=0$ and $W=0$, but $\Delta T\neq 0$? In particular, if there is no change in internal energy, doesn't that imply it is an isothermal process, and therefore that ...
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59 views

Heating a black body

By definition, Black body has absotivity=emmisstivity=1. This means the black body radiates all energy it accepts. Does this mean the black body cant be heated?
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1k views

How temperature gradient is a vector?

Everyone knows Temperature gradient is a vector quantity having direction from cold to hot.My confusion: why is temperature gradient vector if its direction is always fixed (as in the case of ...
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3k views

Plotting the maxwell-Boltzmann velocity distribution in matlab

I'm trying to plot a maxwell-boltzman velocity distribution in matlab. I have also asked this question at cross validated without much luck The PDF is f(v)=sqrt(m/2*pi*k*T) * exp(-m*v^2/2*k*T) ...
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605 views

Why laundry dry up also in cold/frost?

Why laundry dry up also in cold/frost? When you have frost, water in the clothes should freeze, but if clothes are dry, then it should be possible that steam in the clothes does not have time to ...
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1k views

Salt and boiling speed

When we add a compound (salt) to a solvent, the boiling points rises. But, what could we say about the speed the solvent reaches the boiling point? It's better to add salt before or after boiling ...
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1answer
234 views

Is this a simple system in which no heat transfer is possible?

Let's say that a hot gas is trapped in a metal box. This metal box is magnetically suspended in another structure with a low temperature. The inner box does not touch anything. And there is a void in ...
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2k views

What is the most energy efficient way to boil an egg?

Starting with a pot of cold tap water, I want to cook a hard-boiled egg using the minimum amount of energy. Is it more energy efficient to bring a pot to boil first and then put the egg in it, or to ...
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50 views

The 1st law of thermodynamics

If a gas expands adiabatically will the work done be positive or negative? I think it will be positive as $\delta W=p dV$ and we have a positive sign due to the work done by the gas is positive as it ...
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2answers
69 views

Residual Entropy - Third Law

I've been told that many systems possess some residual entropy at absolute zero. This would seem to disagree with the 3rd Law of Thermodynamics? How can this be explained physically speaking? I am ...
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3answers
52 views

Why radiant heat only travels as infra-red waves and not as other types of em waves like UV rays

Heat is a form of energy and em waves carry energy as momentum of photons. So, I think, radiant heat can travel at any frequency. Please correct me.
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8k views

Why change in internal energy is zero in isothermal process

In isothermal process $\Delta U =0$. But I am having trouble understanding it. Say we have an ideal gas, and say my temperature is constant but I move the pressure, volume from $(P, V) \to (P-dP, ...
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101 views

requirements for hydrogen fusion

What are the requirements for hydrogen atoms to go through fusion? Is it a ratio of heat to pressure or are there specific heat and pressure values that must be met (per atom or per mole?) Are there ...
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417 views

Why is the direction of a flame is always upward? [duplicate]

why a candle's flame direction is always upward? What is the coposition of fire? Don't say it's energy. There is something else.
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447 views

Is vapour pressure based on partial pressures or just total pressure on the liquid?

The explanation for the boiling point of water is that at 100C, the vapour pressure becomes greater than atmospheric pressure. But say you had a a jar of water sealed in argon at 1atm, which is larger ...
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734 views

Difference between pressure and stress tensor

What is the difference between hydrostatic pressure and stress tensor?
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310 views

'Polar Vortex' Boiling Water to Snow is Mpemba Effect?

I am based far away from the icy storm currently blanketing the US - the 'polar vortex'. However, I have seen in the TV news footage of reporters throwing boiling water into the air, the water ...
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1answer
75 views

Temperatures at extreme densities

Cosmology (and astrophysics) talk about the "initial singularity" (IS, became the big bang) and "black hole singularities" (BS, inside black holes), and these appear to be quite different: The IS is ...
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904 views

Electric heating rod

I usually heat my bathing water with electric heating rod, I always thought that the base of rod is an insulator so that it can develop high heat. But when I tried touching water while rod was dipped ...
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1answer
758 views

Burning VS Melting: What is the relation in the atomic/molecular structure?

This has never been asked before on this site, so I thought I would ask this to help future searchers, passerbys, or others understand this better. What are the key differences between burning ...
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2answers
755 views

How can a rapid change in the volume of a gas cause changes in its temperature?

We were learning about Boyle's law (pressure is inversely proportional to volume of a gas) and in the experiment to prove the law, we were told that we cannot change the volume of a gas too rapidly ...
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99 views

Why basements stay cold even during summer?

Why a room below the surface (such as basements) can stay cold all the time? How is it able to avoid the high increase of temperature and heat in hot days and periods?
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Is there a heat transfer equation that takes conduction, convection, radiation and dT/dt into account?

I see equations that take 2 or 3 of the listed parameters into account but I haven't been able to find one that is that complete. I'm seeking to solve this equation using matlab for a simulation ...
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26k views

What is the sign of the work done on the system and by the system?

What is the sign of the work done on the system and by the system? My chemistry course book says, when work is done on the systems, it is taken positive. When work is done by the system, it is taken ...
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1answer
3k views

How to calculate incident solar energy on earth in a given day with a spectral filter

The daily solar radiation irradiation is often quoted as being between $3.2 \text{ kW hours}/\text{m}^2$ and $7 \text{kW hours}/\text{m}^2$ per day . If you filter out a range of wavelengths, how can ...
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1answer
464 views

How long does the 2nd pot of water take to boil right after the 1st one finishes?

Say I have a pot of water that boils in 20 minutes, at whatever temperature. If I leave the fire on, take the pot off, pour the hot water into a container, refill the pot with tap water and put it ...
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170 views

Electric power transmission

If we want to transmit electic current for a long distance, we must minimize a heat that releases because of the resistanse. We cannot make a cable wide because it is expensive and it will be massive. ...
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6k views

How do you determine the heat transfer from a P-V diagram?

I doubt this question has been addressed properly before, but if there are similar answers, do direct them to me. I am currently studying the First Law of Thermodynamics, which includes the p-V ...
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1answer
162 views

Liquid oxygen how do they use it as fuel?

Rockets are said to be using liquid oxygen as fuel. How do they use liquid oxygen since it's just oxygen, it only helps in the combustion process. How can it be a fuel on its own?
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1answer
975 views

Why is the equation for Entropy of an ideal gas that undergoes reversible change in T at constant Pressure like this?

Why is the equation for change in Entropy for a reversible change in $T$ at constant $P$ described as $$\Delta S = n C_p \ln\frac{T_f}{T_i}$$
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35 views

What is the cause of the flash of light and debris immediately above this explosion?

First - the footage of the explosion in question: http://www.discovery.com/tv-shows/mythbusters/videos/homemade-diamond-high-speed/ More specifically, about 5 seconds in, I'm speaking of the ...
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1answer
31 views

Heat transfer through radiation and its relation with temperature

My question is: if a body and the surroundings have the exact same temperature, will that body still lose heat in terms of radiation? If so then what exactly is heat. Heat is defined as energy flow ...
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60 views

Expansion of the universe a thermodynamic process or not?

Can the expansion of the universe be thought of as a thermodynamic process? If so, is it a closed system? Is it a reversible system?
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72 views

What is the solution for the apparent contradiction of Second law due to energy fluctuation?

A system has maximum entropy when it has reached thermal equilibrium. But as statistical mechanics say, there is always an otherwise infinitesimal probability of particles to confine at a corner of ...
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1answer
40 views

How does energy flow between two parts of the system that are in thermal equilibrium?

As said by Peter Atkins, Though two bodies are in thermal equilibrium,energy always flows in both direction, but the net energy is zero. Now, how does it take place? I know the macrostate ...
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1answer
53 views

Efficiency larger than one?

The efficiency of a heat engine is the work we can do divided by the heat we take out of the hot reservoir. This quantity is always $ \le 1$. The efficiency of a heat pump is the heat we can release ...
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1answer
48 views

Coefficient of volume expansion for gases

I often read that at 0 degree (Centigrade), gases expand by 1/273 of its volume at 0 degree for one degree rise in temp. So does this coefficient of expansion ( i.e. 1/273) change with temperature?
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108 views

Entropy of a system: microstates and macrostates

Currently we're deriving the Gibbs expression for the entropy during an introductory thermal physics course. We're dealing with a system with $N$ different equally likely microstates that are ...