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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Interface condition for heat exchange

I would like to compute the heat distribution of a piece of metal with some surrounding material. The heat is assumed to propagate by diffusion, so inside the metal piece and also on the outside, the ...
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0answers
128 views

Will humid air mitigate airborn dust due to neutralization of static electricity?

I have came to understand that humid air will help prevent electrostatic forces that can propel dust and cause it to cling to surfaces. My first question: is this above statement true? If the answer ...
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33 views

Does a flame produce free electrons? [duplicate]

Possible Duplicate: Does Fire Conduct Electricity? Why? Is fire plasma? Does a flame produce free electrons ? Or is the answer sometimes depending on the chemicals ? Does the answer depend on ...
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0answers
60 views

Any new texts directly on second law of thermodynamics? [duplicate]

Possible Duplicate: Recommendations for Statistical Mechanics book Is anyone aware of any recent text that summarises the research and arguments on second law of thermodynamics and also on the ...
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0answers
86 views

In a non-degenerate plasma, why are e-e collision negligible compared to e-ion for thermal conduction?

I'm trying to make some order of magnitude estimates of heat transfer in stars - to better understand 1) why conduction is said to be negligible (for non-degenerate matter) and 2) when convection ...
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2answers
447 views

Convergance of a system to Boltzmann distribution

Consider a system with finite-dimension state X and energy E(X), with dynamics which follow the Langevin equation $\frac{dX}{dt}=-\nabla_X{E(X)}+\eta(t)$ where $\eta$ is white noise $<\eta_i(t)\...
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109 views

Temperature of the CMB when the Earth formed and the faint young Sun paradox

The cosmic microwave background (CMB) has a modern temperature of about 2.7 K. At the time of the origin of the CMB, about 13.6 billion years ago, it had a temperature of about 3000 K. ...
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184 views

Dissipation when the temperature is not constant

Consider a process where some chemical species diffuses from one part of a system (which I'll call $A$) to another ($B$) at a rate $r$ $\text{mol}\cdot \mathrm s^{-1}$. If the system's temperature is ...
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244 views

Centrifugal Compressor Flow Rate

For a centrifugal compressor, as found in most turbochargers on internal combustion engines, is there a noticeable change in flow rate versus a naturally aspirated flow rate? In other words, does the ...
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1answer
156 views

How can I calculate the amount of bubbles needed to lift a submerged body?

Our teacher had us come up with our own thermodynamics experiments, so I put a glass of water inside a vacuum-capsule. Inside the glass of water I have placed a non-floating object, a small plastic ...
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2k views

When do I know if energy stored in an object is 0 or nonzero? (Heat transfer)

There is uniform internal heat generation at $\dot{q}=5\times10^{7} \frac{W}{m^{3}}$ is occurring in a cylindrical nuclear reactor fuel rod of 50 mm diameter and under steady state conditions the ...
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2k views

What are typical values of the critical thickness of insulation?

As most people who've had any elementary heat transfer course are aware, when insulating a pipe, wire, etc, there is a critical thickness for the insulation below which it causes greater heat transfer ...
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444 views

Heat equation and Bessel's function [closed]

Could someone please explain why if the time-independent heat equation can, via changing of variables, take the form of Bessel's equation that the $\sqrt\lambda$ should take the values of the zeros of ...
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3answers
627 views

Finite difference formulation of the heat equation with thermal conductivity in 1D

This may seem trivial, but I'm having some trouble deriving the finite difference form of the heat equation with a thermal conductivity function $a(x)$ depending on $x$: $$\frac{\partial u(x, t)}{\...
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0answers
826 views

Why is it when you microwave cold coffee and then add milk it creates a foam head? [closed]

As compared to when the coffee is just hot from brewing. I suspect it has something to do with the way the microwaves are affecting the molecules of the coffee.
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440 views

Maxwell's Demon - laser cooling

There’s an interesting article on Scientific American that tells how to cool individual atoms to within a very tiny fraction of Absolute Zero. It uses two laser beams acting on a very cold rarified ...
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1answer
570 views

Maximum pressure at a compressor outlet and molecular weight

I am puzzled by some data I see for a compressor. From what I read, the maximum discharge pressure reachable with a reciprocal compressor would vary depending on the nature of the gas used, and its ...
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1answer
971 views

how to calculate gibbs free energy per unit mass, per unit volume, and per mole?

I've ran into conflicting information on how to calculate the Gibbs free energy of fuels during combustion per unit mass, volume and mole. A sample solution for hydrogen would be really appreciated!
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1answer
64 views

Why does work done ultimately culminate as wasted heat?

Come to think of it, the work done on a body is converted into some form of energy.But why is it that it ultimately tends to produce heat? In physics we all talk about energy dissipation in the form ...
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3answers
147 views

Where does the energy go when engine braking?

If you're in gear in a car and not accelerating, the car slows down faster than it would from just air resistance and tire deformation. In normal braking, the energy is turned into heat from the brake ...
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1answer
184 views

Which air will give more effective cooling ? Dry or Moist?

Yesterday, I had an innovative idea. I live in India, and in summer season, the temperature can reach up to 45 degree Celsius. We use Split 1.5 Ton AC in our small office. The idea is to put an ...
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4answers
66k views

Heat transfer calculated from the specific heat formula

Say I have 10g of silver, whose specific heat is known to be 0.235. I've heated it up from 50.0C to 60.0C. How much heat has been transferred? The equation is: $$ Q = C_pm\Delta t $$ where Cp is ...
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2answers
2k views

Physics-based derivation of the formula for entropy

I am looking for a derivation of the formula $$S~=~-\Sigma_ip_i \log (p_i).$$ for entropy, from first principles. I only wish to assume the laws of physics, and without involving concepts in ...
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5answers
1k views

Is the atmospheric pressure the cause of a planet's surface temperature or is it the temperature the cause of a planet's atmospheric pressure?

I heard a climatologist on a talk show saying that one of the widely known arguments used by climate scientists to exemplify what a runaway greenhouse effect could cause to Earth's temperature and ...
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4answers
486 views

Irreversible expansion and time reversal symmetry

Suppose there are N non-interacting classical particles in a box, so their state can be described by the $\{\mathbf{x}_i(t), \mathbf{p}_i(t) \}$. If the particles are initially at the left of the box, ...
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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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3answers
9k views

Does closing curtains 'make your home warmer'?

I mean, in the sense that the act of closing curtains would somehow reduce the amount of heat loss of the house to the outside, thus making it warmer for a given supply of heating.
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2answers
1k views

Does the global financial system violate laws of thermodynamics and energy conservation? [closed]

For the past years I am thinking about relating concepts from physics to concepts from economics. Especially since the financial crisis made obvious the instability of the financial system I ask ...
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2answers
812 views

Why is pressure an intensive property? [duplicate]

My teacher explained to me that we volume is an extensive property because it is additive in nature. But he also told us that pressure is an intensive property. Now according to the gas law equation $...
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2answers
982 views

Why does this entropy change formula for heating water blow up at $T_{1}=0$?

My textbook says: Next we consider a more complicated problem: heating m grams of water, from $T_{1}$ to $T_{2}$. The entropy change is $$S_{2}-S_{1}=\int mc_{w} \dfrac{T_{2}}{T_{1}}=mc_{w}\ln\...
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2answers
125 views

Why cannot wood be fully burnt?

Burning wood emits smoke and black. Provided more oxygen or whatever required, can wood be practically burnt fully like petroleum gasses that emits a blue flame and little smoke and little black.
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4answers
721 views

Why are exothermic reactions easier than endothermic?

If we talk about electric heating then we have simple elements in which we apply electrical energy which gets converted into the kinetic energy of the electrons which heats it up. But while cooling, ...
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3answers
2k 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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539 views

Water, can it break through temperature?

If water is heaten up to ridicilously high temperatures, is it possible for the atoms in the molecules to lose their bonds? And if it is possible, isn't this some kind of chain-reaction? Like you ...
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3answers
67 views

Does the thickness of earth's crust accurately correspond with the current proposed age of the earth?

The current model is that earth started as a molten ball of liquid around 4.5 billion years ago. Today, the earth's crust ranges from about 5-50KM in thickness. This is just a layman's opinion, but to ...
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2answers
122 views

Temperature of a Diamond in a Boiling Pot of Water

Suppose I have a boiling pot of water (100 degrees C) and drop a diamond in. Does the diamond eventually reach 100 degrees C? Since the diamond is a rigid structure, its molecules do not vibrate ...
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2answers
2k views

Why Does Air Hold More Water When the Air is Warmer?

I know that when the temperature of the air rises, the maximum amount of Water it can hold before the water condenses to water droplets increases. But why is this - has it got something to do with ...
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3answers
298 views

Asymmetric heat conduction?

So I have this side-view drawing. Now I wonder, will such a multi-layer material have asymmetric heat conduction properties? Namely, because of radiative conduction, reflective aluminum surface ...
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3answers
2k views

Thermal physics question, final temperature of ice and water

Here is the question from my textbook: "In an insulated vessel, 250g of ice at $0^{\circ}$C is added to 600g of water at $18^{\circ}$C. What is the final temperature of the system?" The solution ...
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3answers
712 views

Mathematical proof of non-negative change of entropy $\Delta S\geq0$

I understand that we can prove that for any process that occurs in an isolated and closed system it must hold that $$\Delta S\geq0$$ via Clausius' theorem. My question is, how can I prove this in a ...
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3answers
593 views

Problem with an electricity / thermodynamics assignment

I've been trying to figure this one out for a while on my own, so I'd like to ask for your help if you could offer some. The task states: A heater made out of a wire with a diameter $R = 0.2\text{...
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2answers
404 views

Restrictions on defining microstates (Entropy)

If we have an isolated system $Sb$ with thermodynamic entropy $Eb=X$ (and growing by the 2nd law of thermodynamics), we could define an abstract system $Sa$ (containing the system $Sb$) but define ...
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3answers
86 views

Boiling as apparent violation of the second law of thermodynamics

One of the statements of the second law is that no agency can be built whose sole effect is to convert some amount of heat entirely to work. But in case of boiling, the temperature being constant, ...
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2answers
152 views

Is this conceptualization of blackbody radiation logical/correct?

From what I understand, a blackbody is a body which does not emit radiation as a result of atomic excitation/relaxation but rather solely due to the kinetic energy of its particles due to interactions ...
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4answers
136 views

The impatient hot tub owner [closed]

An impatient man owns a 300 gallon hot tub. He comes home from a hard day of work and sees that his hot tub is currently simmering at 90F. For maximum relaxation, he wants it at 104F. However, the hot ...
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3answers
119 views

Can you huddle next to a fridge in sub-zero temperatures and keep warm?

There's a saying I've heard in so many places.. "It was so cold that we used to huddle next to our refrigerator to keep warm..." I had heard this phrase uttered some 30 or so years ago, and it's stuck ...