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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915 views

Temperature change: boiling pasta in a lot of water or a little

SeriousEats gives a not-very-scientific representation of what looks like a thermodynamics calculation: Want to hear something even more interesting? Folks will occasionally say that "using a ...
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5answers
7k views

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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1answer
344 views

Definition of entropy in nonequilibrium states

Thermodynamical definition of entropy $$S(p)=-\int p\ln p~dx$$ is defined only on equilibrium system. But why can't we use it for non-equilibrium system? Is there a well-accepted definition for it?
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2answers
309 views

Paradox while Cooling & Heating in Air? [duplicate]

I was thinking about how asteroids get "burned" up in the upper atmosphere as they approach the earth surface due to the atmosphere of earth heating the asteroids immensely as a result of air ...
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1answer
332 views

How to calculate the heat transfer rate between the liquid and the gas?

Let water (liquid) be in a chamber (with no heat transfer to the walls). The gas is the residual space above the liquid, meaning that the contact surface is the surface of the water. Given the gas ...
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2answers
88 views

Thermodynamics of scattering theory

I have a couple of conceptual questions regarding the thermodynamics of scattering. Any partial answer or argument will be appreciated. For the sake of discussion, consider the scattering of ...
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3answers
510 views

How do objects heat up?

If every body emits radiation at a given frequency and temperature exactly as well as it absorbs the same radiation, how do objects heat up?
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1answer
518 views

Are pressure and volume not independent properties in liquid water?

Every thermodynamics textbook teaches us that, for a simple compressible substance, any two independent properties will suffice to determine the system state. Those can be pressure and temperature (...
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3answers
169 views

Is there a minimum energy content of information, other than 0 Joules?

Lets say I want to send the bit string 010110 to someone. Is there a theoretical lower bound on the energy needed to do this?
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1answer
166 views

Spontaneity / Free Energy of Non-Isothermal Process

I'm trying to determine a lower bound for the work input necessary to make an entropy-reducing process "spontaneous" in the sense that the 2nd law is not violated. For a constant temperature and ...
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1answer
372 views

Showing the thermal expansion coefficient is the sum of the linear expansion coefficients

Given that the thermal expansion coefficient is defined as: $$ \beta=\frac{\frac{\Delta V}{V}}{\Delta T} $$ and the linear thermal expansion coefficient is defined as: $$ \alpha = \frac{\frac{\Delta L}...
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1answer
52 views

$\mathrm{CO_2}$ rate of deposition

Parts of Antarctica average -127°F (-83°C). The freezing point of $\mathrm{CO_2}$ is -109.3 °F (-78.5 °C). If one could construct a large container at such a place shielded from the sun, would ...
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1answer
952 views

How cold would a bowling ball near absolute zero make a room?

If a bowling ball at absolute zero suddenly appeared in my room, how cold would the room get? Would I die? My initial estimation is that it one bowling ball at 0K (i.e., 300K below room temperature) ...
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1answer
273 views

Why do metal surfaces reflect thermal signature?

I recently borrowed a thermal camera from a friend and I tried to observe my palm print over a reflective metallic plate. When I looked at it through the camera, it reflected my thermal signature too. ...
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3answers
1k views

How are heat transfer rate and heat capacity constant of a material related?

How are heat transfer rate and heat capacity of a given material is related? When I was a kid I imagined it like "Capacity is like a container or bucket of some sort, if it gets filled easily it can ...
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2answers
110 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
54 views

Followup to: The relation between energy quanta of an Einstein solid and the equipartition value of heat capacity

As a followup question to this question: The relation between energy quanta of an Einstein solid and the equipartition value of heat capacity and this answer http://physics.stackexchange.com/a/133053/...
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3answers
221 views

Ice and liquid water interacting across a boundary

Imagine we have two thermodynamic systems, one a mass of ice and the other an equal mass of liquid water, with both at 273.16K. Each system is isolated, except that they can interact with each other ...
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1answer
216 views

The relation between energy quanta of an Einstein solid and the equipartition value of heat capacity

Consider an Einstein solid with quantized energy values $U=q\epsilon$ and $N$ oscillators. I calculated some values of an Einstein solid numerically through a function in R (at the bottom of the post)....
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2answers
256 views

What are the contributions of the Non-equilibrium Thermodynamics?

I am very interested in Thermodynamics, but though it is easy to find good books and information about classical thermo, it seems that is not the same for non-equilibrium thermodynamics. I would like ...
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1answer
144 views

Why is everything colder nowadays? [duplicate]

I know that when the universe began it was incredibly hot. Ever since, it is been cooling, and nowadays the average temperature of the universe is quite close to 0 K. Is this a consequence of having ...
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2answers
313 views

Is the second law of Thermodynamics an immense tautology?

Let's imagine for a second a system that is changing constantly from one microstate to another one. It could be a given volume of a gas with its atoms moving and bouncing around, or a deck of cards ...
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3answers
561 views

Axioms behind entropy!

The concept of entropy is very ubiquitous, we learn about its uses starting from Information Theory (Shannon entropy) up to its basic definition in statistical mechanics in terms of number of micro-...
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0answers
27 views

Third principle of Nernst [duplicate]

I wonder how can I prove the fulfillment of the third principle of Nernst of a body that obeys the next expression.
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1answer
85 views

Scale down model of a refrigerator

I am teaching Thermodynamics. For teaching how refrigerators work I am looking for a working model of a scale down refrigerator. This should be as close to real as possible but very small in size. Can ...
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1answer
409 views

Calculating new temperature of an object when air temperature changes

I'm trying to calculate the new temperature of an object when the air temperature around it changes, given a period of time. Basically I get periodic readings from an air temperature sensor in a ...
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2answers
3k views

Latent heat of vaporization at non-boiling temperature

The latent heat of vaporization of water is what we normally use to calculate the heat transfer that occurs at 373 K when liquid water transits to vapor phase. But there are curves for latent heat of ...
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0answers
143 views

What are the thermal properties of a “perfectly rigid” container?

can a "perfectly rigid" container be a diathermal boundary? I checked the wikipedia article for heat and read: Kinetic theory explains transfers of energy as heat as macroscopic manifestations of ...
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1answer
100 views

If you dig a deep tunnel, will the rock sublimate?

If a tunnel is dug deep inside the crust (but before reaching places where the rock is liquid), how will the enormous downwards pressure manifest itself? Will the difference in pressure $(\rho_{rock}-\...
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2answers
90 views

Is Rosehip Syrup boiling in a bottle?

My wife made Rose-hip syrup and the final part was boiling it in a saucepan. While still hot she placed it in a glass bottle. To keep it sterile she plugged it with a wine-saver top and sucked out ...
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1answer
1k views

Gravity and the Second Law of Thermodynamics [duplicate]

I was wondering about the hypothetical - and apparently improbable - heat death of the Universe when I stumbled upon this seeming contradiction. A certain volume of space with a uniform distribution ...
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1answer
227 views

Calculate heat transfer out of a basement [closed]

I am thinking it should be possible to calculate heat loss out of basement based on the temperature of the walls, but am not sure how to do it (what the equations are). For example, lets say the ...
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1answer
49 views

Variable area manometer duct

How does one measure the pressure at the end of the manometer tube when the manometer tube itself is having a variable area?
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2answers
3k views

Do all liquids boil in a vacuum?

Water boils at positive temperatures when put into a vacuum. Is this the case with all liquids, e.g. mercury?
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3answers
144 views

How many volcanic eruptions would be necessary per year to neutralize global warming?

Volcanic eruptions sometimes cool the earth. How many eruptions of what magnitude, locality and type would be required per year to neutralize Global Warming?
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0answers
56 views

How powerful would a series of rail guns or bombs need to be to destabilize a hurricane?

In an effort to destabilize hurricanes by burning the necessary cold zones it has been proposed that planes drop various carbon trash on them. That seems like a minor amount of heat change over a ...
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1answer
182 views

Partial Pressure - Which solution is right?

Question: Carbon dioxide (1.100 g) was introduced into a 1.00 L flask which contained some pure oxygen gas. The flask was warmed to 373 K and the pressure was then found to be 608 mmHg. If CO2 and O2 ...
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1answer
111 views

Irreversible work

I'm having some trouble trying to find the irreversible work done by a perfect gas when expanding. I know that the reversible work is greater than the irreversible one, but how can I find the ...
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2answers
231 views

Problem regarding heat engines [closed]

We have two different set ups: A 200K brick in a 300K environment A 300K brick in a 200K environment From which one of these can you extract more work? Assume equal mass and heat capacity. Using ...
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4answers
226 views

why are the square of the components of velocity equal?

In Principles of Physics by Resnick,Halliday,Walker, when evaluating the $v_{rms}$ ,they first found $p = \frac{nM(v_x)^2}{V}$ & then substiuted $(v_{avg})^2 = \frac{1}{3} .v^2$ where $v^2 = (v_x)^...
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2answers
319 views

Who invented the perfume bottle thought experiment?

A common thought experiment used to explain the second law of thermodynamics, the "arrow of time", etc. is perfume escaping from an opened perfume bottle; the perfume is likely to diffuse into the ...
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1answer
2k views

Thermodynamics for Dummies: Entropy and temperature

I do not study physics and I have never had a course in thermodynamics. I have no idea what it is about, but I am currently taking a course where we had something about entropy. Would be great if ...
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0answers
338 views

Coarse graining on measurement vs phase space (second law)

I've followed Leonard Susskinds series on "the theoretical minimum". In the entropy/reversibility episode in statistical mechanics, he explains (at least one way of) how the apparent paradox of ...
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2answers
282 views

Liquid column “recoils” in a sealed cylinder when hit by a piston — is it possible?

Consider a cylinder filled partially with a liquid (e.g. water). The cylinder is sealed, and is at held at room temperature (e.g 298K). At equilibrium (or when no external disturbance is imparted to ...
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3answers
2k views

The thermodynamics of heating water in a rigid container

When the pressure on the liquid surface is less than the vapor pressure of the liquid at a given temperature, the liquid will start to evaporate. This is common sense. The problem is more difficult ...
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3answers
479 views

Is it possible for an electrical device to generate more heat than another using less power or the same?

People are claiming that a Plasma TV uses more power which explains why it uses more heat. We refer to power as wattage in this regard. Countering this, is it possible that a device can draw the same ...
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3answers
867 views

Is Fourier's law of conduction a consequence of the second principle?

In classical thermodynamics courses, entropy is often motivated by the need to justify that heat flows from high temperatures zones to lower temperatures zones: this is seen as a consequence of ...
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3answers
3k views

Zeroth Law of Thermodynamics, temperature, and ordering

In my thermodynamics course (and in other places on the internet) it is asserted that the Zeroth Law of Thermodynamics can be used to define the concept of temperature. One statement of the Zeroth ...
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2answers
67 views

Thermometer reading

I quickly plunged a room-temperature thermometer into very hot water, the mercury level went down briefly before going up to a final reading. Why?
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4answers
458 views

How to measure the energy consumption class of a home appliance? [closed]

Some of you may be familiar with the EU energy consumption classes for domestic appliances (or equivalents in other areas). Let's say we have a domestic appliance which was made before the energy ...