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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880 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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2k 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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2answers
427 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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1answer
804 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
216 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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5answers
1k 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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2answers
79 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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4answers
146 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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387 views

Difference between pressure and stress tensor

What is the difference between hydrostatic pressure and stress tensor?
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1answer
69 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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3answers
526 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
382 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
371 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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1answer
91 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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947 views

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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3answers
11k 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
2k 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
302 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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2answers
131 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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3answers
4k 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
153 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
738 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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2answers
57 views

How to model an apartment's airconditioning?

Background: This reminds situation reminds be of an episode from the The Big Bang Theory, although it is quite different from it. My roommate and I have similar temperature preferences and also share ...
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2answers
63 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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1answer
70 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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1answer
36 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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43 views

Question about Charles' law:

Charles's law says that the volume of a given mass of a gas is directly proportional to its absolute temperature. This means if we increase one, the other one is automatically increased. So the ...
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3answers
75 views

Latent heat of condensation

Regarding atmospheric processes, I understand that energy is required to evaporate water by moving molecules further apart i.e. a phase change from liquid to gas. The air then ascends into the ...
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4answers
1k 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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2answers
76 views

What is the principle of equivalence in thermodynamics?

I've been searching for this for a while. There is a principle of equivalence in general relativity: http://en.wikipedia.org/wiki/Equivalence_principle But I need the principle of equivalence in ...
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1answer
70 views

Comparing unknown temperature scales [closed]

Source: Principles of Physics by Resnick, Halliday, Walker. $9^{th}$ edition. Chapter 18. Problem 6. On a linear $X$ temperature scale, water freezes at $-125.0^0X$ and boils at $360.0^0X$. On a ...
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2answers
250 views

Auto-refrigeration

I'm reading about the auto-refrigeration effect and can't find a really good explanation. Is the idea that when you have your condensed liquid, and then release it into a low pressure environment, ...
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1answer
223 views

Do ideal gases at zero Kelvin have potential energy?

Do ideal gases at zero Kelvin have potential energy?
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3answers
2k views

Why does a human body only emit infra red radiation and not other types of electromagnetic radiation?

What causes humans to emit infra red radiation and why don't we also emit other types of electromagnetic radiation such as ultra violet or microwave? Sunlight contains UV and our body takes it in, but ...
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1answer
256 views

Why do real gases deviate from ideal behavior above the Boyle temperature?

My textbook says that Boyle temperature is the temperature at which a real gas shows maximum ideal gas behavior. Below the Boyle temperature, molecules come too close and intermolecular forces skew ...
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1answer
48 views

Why does black get heated the most? [duplicate]

I found out black heats up the most and white the least, as I expected. The question I had is that despite black reflecting all the wavelengths of the visible spectrum, and hence giving the black ...
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4answers
235 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
61 views

Spreading heat with water

If water is cycled through a thin pipe by a pump, and a certain spot on that pump is made of thin copper that is being heated by a 1000 C source, will the water, as a whole, attain a heat of 1000 C ...
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2answers
114 views

Debye temperature for the steel?

I'm looking for data on Debye temperature of steel (ideally with a known carbon concentration, structure, and set of phases), but find only data on elements. Do You happen to meet the data in papers, ...
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1answer
97 views

Air conditioners and the law of conservation of energy?

Sorry if this is a stupid question, but I have often been told that air conditioners are more efficient than an electric heater, because, the story goes, if you put say 1 kW of electricity in the ...
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2answers
117 views

Can you confirm 2 simple statements about vaporization?

Vaporization is an interesting engineering subject, but unfortunately much about it has always been unclear to me. Recent research of mine has brought my mind to link vapor pressure to boiling and ...
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1answer
257 views

How to determine the amount of light energy (photons) being released from an incandescent light bulb?

I have got this all down pat: 1.Collision with a moving particle excites an atom. 2.This causes an electron to jump to a higher energy level. 3.The electron falls back to its original energy level, ...
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2answers
260 views

Does heat radiation come from the nucleus or the electrons?

Is more of the thermal radiation due to acceleration of electrons or acceleration of the nuclei? Do electrons and nuclei carry the same fractions of thermal energy in a hot body?
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2answers
100 views

Dividing values with units

I'm reading about the subject of heat in a basic physics book. If I am not mistaken the formula to work out how much energy is required to increase the temperature of water is ...
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1answer
133 views

If a balloon is continuously filled with air and stays at a constant shape and size will there be any empty space in the balloon?

If a container like a balloon but with constant volume is filled, is it possible to pack air molecules so closely together that they don't have any empty space between them? If so, what would this ...
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3answers
342 views

How can anything be hotter than the Sun?

I've heard that if a space shuttle enters the atmosphere from a bad angle its surface will become so hot that it will be hotter than the surface of the Sun. How can that be? It seems to an uneducated ...
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2answers
127 views

gravity affecting a molecules speed? [closed]

Why are the poles colder than the rest ofthe planet?Is the gravity stronger making molecules spin slower?How does gravity affect heat and hydrogen bonds? And what affects gravity?A little off topic ...
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1answer
74 views

In $PdV$, what is the value of $P$? $P_1$ or $P_2$?

Say I have an ideal gas that has a known $P_1$, $P_2$, $T_1$, and $T_2$ undergoing a reversible adiabatic process. I want to find the work done so I must use $PV = RT$ to get the change in $V$, so ...
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1answer
95 views

Landauer's principle vs Wien's displacement law

Can we argue based on Landauer's principle that if one bit information is changed inside a blackbody, the total radiated energy should be at least or in order of kTln2? If it is so, can we also argue ...
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1answer
125 views

What happens to the time it takes for my noodles to cook, and the temperature of the boiling water?

I have a boiling pot of water that I am going to cook my Sponge Bob Noodles in. I am very hungry and want the noodles to cook faster, so I turn up the heat from medium to high.( Note, the water was ...