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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What is the smallest engine theoretically possible?

Is there some law of physic forbiding small engines that use say petrol? I would like to know of some analogy between electric motors and heat engines. In the latter we can make a motor so small that ...
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10 views

Can super heated air be used to drive a turbine driven engine?

Air a mixture of gases is ever trying to expand. By accelerating this property can air be used as a fuel in a turbine driven engine which can give sufficient output to be used in an automobile.
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15 views

Activation energy as a function of defects

Electrical conductivity has a form of Arrhenius equation. It is assumed that activation energy decreases with defect density in the insulating state and becomes zero in the conducting state. Can one ...
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6 views

Calculating/estimating heat transfer losses for hot air balloon (lantern)

I'm trying to build a flying lantern / hot air balloon that flies as close to hovering as possible (as opposed to up-up and awaaay). To see if this is feasible I'm trying to simulate as much as I can ...
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18 views

Is equilibrum condition consequence of second law of thermodynamics?

Equilibrum state is generally stated to be most stable state. Is equilibrium state consequence of second law of thermodynamics at microscopic level. i.e a system tends to reach the equilibrium state ...
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1answer
34 views

Is it possible to tell time within a steady state?

(Inspired from this question (A) which unfortunately the link in the selected answer is now 404 broken (which might have contained my answer), thus cannot read any deeper than that) From the above ...
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1answer
50 views

Energy conservation of permanent magnets engine

How to explain the fact that magnet can attract an object (apply a work W) without losing a (significant) part of its internal energy? How to apply the energy conservation principle? Please think to ...
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1answer
24 views

Why does this derivation of the dependence of free energy on pressure not work?

It is well known that the Gibbs Free Energy of a gas depends on the pressure via the following formula: $$G_m(p) = G^\circ_m + RT\ln{\frac{p}{p^{\circ}}}$$ Where $G_m$ is the molar gibbs free energy ...
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1answer
10 views

Energy under constant pressure and temp

Conceptual problem: let A + 2B -> C + 2D be a reaction under constant pressure P and temp T, that goes all the way towards the products. A,B,C,D are ideal gases. let $\Delta H$ be the molar enthalpy ...
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4answers
50 views

Fall in temperature due to expansion

The following lines are from my book. The gas is heated and allowed to expand at such a rate that the fall in temperature due to expansion is less than the rise in temperature due to the heat ...
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42 views

Are there any equations describing solid, liquid, or plasma containing the gas constant $R$? [on hold]

The gas constant $R$ relates so much to Boltzmann constant $k_B$. Boltzmann constant= gas constant divided by the Avogadro constant. For example, $R$ can be used in Nernst equation. So, $R$ is not ...
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11 views

Determination of “Heat transfer coefficient” between block of aluminium and air

I need to build a temperature control system for a hot plate of aluminium, which I intend to heat with an electric cartridge, and the temperature I would be measuring with a PT100 to close the loop. ...
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Entropy change of mixing

$dU = Tds - PdV$ definition of internal energy $dU)_{V} = TdS$ internal energy change at constant volume $-C_{v} \Delta T = T_{1} \Delta S$ integrating, assuming that $C_{V}$ is invariant through ...
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1answer
15 views

What is an expression/physical law that relates high frequency thermal fluctuations to gas pressure?

When a gas is compressed the 'ideal gas law' can predict what the increase in gas temperature will be. But that's just a mean temperature, right? At a quantum level the frequency of molecular ...
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63 views

Does Expanding Universe conflict with the Thermodynamics 3rd Law? [duplicate]

I know that thermodynamics 3rd law states that if a system in equilibrium is at zero temperature, its entropy is minimum. Expansion of the universe made a transition from radiation dominated era ...
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1answer
69 views

Entropy - does Heat Death occur in a closed system

Does heat death occur in a closed system? (Assuming you can theoretically have some sort of "closed system".
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1answer
37 views

Efficiency of a real engine

Can anyone tell me what is wrong with the following argument? Consider a Carnot engine and an engine $X$ whose efficiencies are $\eta_c$ and $\eta_x$ respectively. Let us assume that ...
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26 views

An interesting question on the mass of a droplet of liquid experiencing the Leidenfrost Effect

Background and Inspiration: I have seen numerous demonstrations of the leidenfrost effect, both on the internet and in my mother's kitchen. But I started wondering about a general case after having a ...
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19 views

Refrigeration Apparatus flow meter location [on hold]

What would be the reasoning for locating the flow meter in it's location in the following refrigeration apparatus (from a thermodynamics perspective):
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1answer
29 views

in which part heat travels faster

A room has one wall made of concrete, one wall made of copper, and one wall made of steel. All of the walls are the same size and at the same temperature of 20°C. Which wall feels coldest to the ...
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1answer
34 views

Why is my breath hot when i open my mouth all the way, but cold if I blow like a whistle? [duplicate]

I observed this as when I want to cool my soup I blow like a whistle and when I want to warm my hands I open my mouth more as my breath is warmer now.
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0answers
35 views

Thermodynamics - Efficiency of an engine [on hold]

I am taking a mathematical physics course and got stuck on this rather simple problem Consider a thermodynamic cycle of monoatomic gas () I want to calculate efficiency of this cycle I know that ...
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1answer
46 views

Is the gas constant really a constant?

For ideal gases we have $$ C_p-C_v=R $$ now the left hand side of this equation is temperature dependent, so how is it possible that gas constant $R$ is temperature independent?
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5answers
3k views

Why does my fireplace shoot flames out the front until I open my backdoor?

I have a natural gas fireplace with fake logs in it. I open the flue, turn on the gas for a couple seconds, and throw a match in. The flames kind of go up and out of the flue, but most of the flames ...
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24 views

Is using molar terms with maxwells relations misguided?

My professor wants me to do a lot of derivations using maxwells relations. One of the things he wants me to prove is that from the Van der Waals equation of state one can say: $\Big(\frac{\partial ...
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2answers
58 views

An equation to describe a process of heating one room using hotter air from another room

There are two rooms completly isolated from the outer world (a closed system, no heat losses). They are connected with each other through a ventilation tube. Temperature in room A is 32 degrees ...
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2answers
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
65 views

Are black holes hot?

If no light can escape black holes, in my mind they would act as a greenhouse, collecting radiation from the stars or CMB or anything. Or is all this energy just absorbed by the black hole?
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2answers
100 views

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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2answers
1k views

Where does information go if thermodynamic death?

Often read that until Hawking the black holes were introducing a problem with information. Allegedly information should be unable disappear, while this was happening in classic black holes. What ...
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14 views

Kettle barbecue thermodynamics question

I have an old kettle barbecue which lost its legs to rust. I then placed the dome on top of a truck's brake drum and throttled the airflow by mounting the brake drum on a plate with holes drilled in ...
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1answer
31 views

When will internal energy change?

If a gas expands irreversibly and adiabatically from $(V_i, p_f+const)$ to $(V_f,p_f)$ will the internal energy change? I have two thoughts: 1) Yes because $\Delta E= \Delta Q + \Delta W$ always ...
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1answer
55 views

The fly and the sphere of iron

When I was a child, I read something like the following in a book whose name I have now forgotten (I tried to find the original quote on the web, but although there are some similar passages the ...
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2answers
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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2answers
37 views

Can an object appropriately isolated from its surroundings become colder than its surroundings?

Consider a sealed box, well-insulated on all sides, except for the lid which is transparent to infrared. An object is placed inside the box and the box is evacuated (purpose being to thermally isolate ...
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85 views

Does This Video Really Prove that Energy Conservation Can Be Violated? [closed]

I've discussed the following video elsewhere: http://youtu.be/YBMUzoUJ7ww and am more and more coming to the conclusion that the video shows for the first time scientifically sound proof that ...
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24 views

Melting icicles

If I break off the bottom half of an icicle, will the top half melt faster?     ...
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1answer
2k views

When heat is applied to the top of a stack of pennies, why does the bottom penny melt first?

I just watched this video where a blow torch is used on the top of a stack of pennies. I'd like to know why the bottom penny melted first.
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2answers
585 views

Is it possible to disprove water memory with an entropy argument?

Water memory was a controversial experiment claiming to provide an explanation supporting homeopathy. The results were largely dismissed as being tainted by experimental error. One possible mechanism ...
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30 views

When did the casual definition of the three laws of thermodynamics first appear? [closed]

Who is credited as the source, and when were the laws first stated in this form? (1st Law) You can't win. (2nd Law) You can't break even. (3rd Law) You can't get out of the game.
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1answer
39 views

Does $\delta W=pdV$ hold for non-ideal gases

I have that for quasistatic processes, $$ \delta W= \textbf{f}\cdot d\textbf{x} $$ so for a gas $\delta W=pdV$. Does this only hold ideal gases or will it hold for van der waal's gas?
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2answers
78 views

Finding Maxwell relations

I feel I am missing something about deriving Maxwell relations. I have read http://ocw.mit.edu/courses/physics/8-044-statistical-physics-i-spring-2013/readings-notes-slides/MIT8_044S13_notes.Max.pdf ...
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1answer
14 views

Cooling effect of sipping

Is the primary action of cooling of a sipped hot fluid explained by the reduced flow of the hot fluid, the air cooling of the fluid as it is sipped or another factor?
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0answers
14 views

Equation of State of PVT system

Find the Equation of State of a fluid with Volume expansivity $\alpha_P$ and an isothermal compresibility $\kappa_T$ are given by $$\alpha_P=\alpha_0 \Big(1-\frac{P}{P_0}\Big) \\ \: \: \: \: ...
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2answers
362 views

Temperature of space

What will be temperature inside an isolated box in empty space? By isolated I meant light from stars cannot enter the box and there is no matter inside the box.(no vibrations or movement of molecules ...
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1answer
60 views

Entropy and the $2^{nd}$ law of thermodynamics

I have just been introduced to the word "entropy" and as it is my understanding that it is a measure of the randomness and chaos of particles in as system. My textbook list the 2nd law of ...
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0answers
18 views

Isothermal Expansion in Real Gases

I understand that for a ideal gas in the case of reversible isothermal expansion, $\Delta U=0$ and $-Q=W$ but in case of a real or van der Waal gases, how can I find $Q$, $\Delta U$ and $\Delta S$?
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1answer
43 views

What sort of math deals with thermodynamics inside of semiconductors?

That is to say, how would one consider the thermodynamics of a complex chip like a modern CPU? I hear that designing the thermal efficiency of such systems is very difficult. I'm not sure why, ...
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1answer
34 views

How to thermodynamically understand process of burning a piece of coal?

Let's imagine that I have a match in hand and nugget of coal on my desk. Then I light up the match and place it for few seconds near the coal so a tiny piece of nugget catches fire. Then another piece ...
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1answer
31 views

Dielectric heating - does EM field transfer energy to polar molecules?

In AC field, polar molecule are trying to align with external field. At high freguencies, changes of field are so quict, that molecules cannot align with it. This leads to increasing kinetic energy of ...