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's the relationship between the energy density of a black-body and its radiant exitance?

Through a bit calculation we can derive that in a cavity, the energy density $$u(f,T)=\overline{E(f)}\times G(f)=\frac{8\pi h}{c^3}\frac{f^3}{e^{h\nu /kT}-1}$$ If we take the integral over all ...
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2answers
245 views

Thermalisation - Open quantum systems

I would like to understand better a phenomenon of a quantum heat bath. Below I present one example, which seems quite clear to me. It would be great to see some less-discrete models, and more ...
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1answer
170 views

Is there valid physics behind the bodybugg?

The bodybugg is a faddish gadget whose marketers claim it can measure your body's daily energy expenditure. Their sales literature says: As reported in the British Journal of Sports Medicine, 2008 ...
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2answers
383 views

Why does Platinum evaporate if left long enough?

I have been reading into research relating to the redefining the 1 kg weight as the current Platinum-Iridium is becoming smaller. In this article, here, it mentions that the original metal weight ...
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1answer
161 views

What is the net radiative balance between two blackbodies with different temperature?

Context In trying to understand a crop productivity model, I want to figure out how to derive the equation for the net exchange of longwave radiation between two adjacent blackbodies (soil and ...
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0answers
70 views

How can we calculate heat transfer through hot gas to moving thermic fluid? [closed]

Heat is to be transfer from $CO_2$ gas to fluid. $CO_2$ is being heated by solar energy. How can we calculate heat transfer from the hot $CO_2$ gas to the moving fluid?
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1answer
168 views

Do ice crystals grow only as heat is being removed or also when an item is at a set temperature?

Chicken develops ice crystals between -2C to -4C. Now as chicken's temperature moves slowly from -2C to -4C ice crystals will grow. However, let's say that in a freezer, we set the final temp to -3C. ...
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2answers
594 views

How does a gas of particles with uniform speed reach the Maxwell-Boltzmann distribution?

Take an empty container and fill it with $N$ gas particles (ideally a monoatomic gas), each having the same kinetic energy $E$, then isolate the container. Since initially the speeds don't follow the ...
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2answers
362 views

The statistical nature of the 2nd Law of Thermodynamics

Ok, so entropy increases... This is supposed to be an absolute statement about entropy. But then someone imagines a box with a 10 particle gas, and finds that every now and then all particles are in ...
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60 views

Which pressure to use in the $T~ds$ equation?

Let's say I have an adiabatic, rigid, open container that has an amount of air at some pressure, $P_\text{cv}$, and some temperature, $T_\text{cv}$. I have heated pressurized air coming into the ...
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3answers
239 views

Shouldn't the sign of generated entropy always be positive?

I have a process where 10 g of liquid lead at 400 C is dropped into a water bath that is at 25 C. The lead solidifies over time and comes to thermal equilibrium with the water bath. The bath is so ...
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172 views

How does heating cause motion?

W.R.T. Newton's laws a force is required to change the state of rest of a body. Then how does heating cause a particular object's atoms and molecules to wiggle ? What is the force being applied when ...
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3answers
2k views

What is the Units for Thermal conductivity?

What are the units for thermal conductivity and why?
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1answer
113 views

Water coolso object by heat absorption [duplicate]

Why do water of water based liquids like sweat cool objects? The most clear example I have is the sweat on the skin. I learned that it absorbed heat because it evaporates, but this is something ...
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0answers
125 views

Which cosmological models support the Boltzmann Brain Paradox?

In this article, they mention that the Boltzmann Brain paradox is supported by 'the best cosmological models.' However, it gives no references, and I haven't found any by a Google search. I was ...
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0answers
352 views

Making an equal amount of positive and negative energy?

I was wondering if it would be possible to create an amount of positive energy out of a vacuum, in addition to an equal amount of negative energy, thus not violating the first law of thermodynamics, ...
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1answer
298 views

Why do humans like to break the second law of thermodynamics? [closed]

Roughly speaking, Entropy is a measure of the disorder of a system. However as humans, we tend to do the complete opposite. For instance, in a home if a painting that is hanging on the wall is ...
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85 views

Best material for heat transfer between ice and water

What is the best container material for heat transfer between ice and water? this is a difficult question to ask without displaying a picture of what I'm meaning.
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1answer
432 views

What sense can be made of the natural logarithm in physics? [closed]

What sense can be made of the natural logarithm, When appearing in a physical process? For example, This integral in the thermodynamic $\int_i^f \frac {dV}{V}=Ln\frac {V_f}{V_i}$ when $V$ denotes ...
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5answers
2k views

Perpetual motion machine of the second kind possible in nano technology?

First of all sorry for my English - it is not my native language. During my engineering studies at the university the thermodynamics professor told us that the "second law of thermodynamics is not ...
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1answer
216 views

What is the physical basis behind thermal diffusion in a Clusius-Dickel column?

A Clusius-Dickel column allows separation of two species by the application of a thermal gradient. In its simplest form, two bulbs are maintained at two different temperatures $T_1$ and $T_2$ and ...
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2answers
227 views

Second law of thermodynamics implies a linear cosmology?

If one applies the second law of thermodynamics to the Universe[1] as a whole then one might expect that the entropy of the Universe always increases as time goes forward (or more accurately that the ...
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99 views

Evidence of atoms from Dulong–Petit law?

All materials have same molar specific heat, cf. the Dulong–Petit law. Is it an evidence of atoms? What other examples are there for atomic theory?
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4answers
4k views

Why does boiling water in the microwave make a cup of tea go weird?

When I boil water in the kettle, it makes a nice cup of tea. Sometimes I need to use a microwave because a kettle isn't available. I boil the water in the mug and it looks pretty normal, but when I ...
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1answer
207 views

Do bifacial solar panels operate at lower temperature than normal solar panels?

Bifacial solar panels have a glass backplane instead of the usual aluminum and are designed to absorb and convert to electricity light incident on either face. Many manufacturers claim that their ...
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1answer
626 views

Stress due to the mismatch of thermal expansion coefficients of two different attached materials

I'm simulating the thermo-electro-mechanical behavior of a copper wire which is surrounded by silicon dioxide. In other words, the wire segments is under mechanical and thermal loads and at the same ...
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2answers
281 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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286 views

Would this pump water up? and if so, how far?

I had this idea of an osmotic pump way back in high school and I never got a satisfactory answer if it would work. If I had this configuration: Would it continually pump water up given ambient ...
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2answers
393 views

Boundary between supercritical fluid and gaseous phase

As far as I understand, going around the critical point, it is possible to transform a liquid into a gas without seeing a phase transition. Does this also mean that there is no clear separation ...
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0answers
31 views

Is there a thermodynamic law or theorem that expresses how systems “break” or “change” when enough energy is added?

I have a simple question about thermodynamic laws, and I am hoping you can help me. Let's say that I have a sphere container with some pressurized gas in it. I can slowly increase the pressure over ...
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1answer
6k views

Thermodynamics: Are pressure and temperature enough to calculate enthalpy?

From the chart above, it looks like it is possible to calculate enthalpy from just pressure and temperature. After a few hours of Googling my question, I'm not able to find anything helpful. My ...
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2answers
953 views

When is temperature not a measure of the average kinetic energy of the particles in a substance?

I had always thought that temperature of a substance was a measure of the average kinetic energy of the particles in that substance: $E_k = (3/2) k_bT $ where $E_k$ is the average kinetic energy of ...
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1answer
58 views

Fourier rate equation valid in which frame of reference?

I wonder about the following; the Fourier rate equation of heat conduction states: $$\vec q = -k\nabla T$$ But I'm wondering if this is valid in every frame of reference, because the heat flux $\vec ...
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1answer
102 views

Explanation Needed: Thermodynamics of a hot/cold water jet machine

I didn't know where to begin with this problem. I eventually found a solution online, which is why I'm reposting this question with an answer. I was wondering if anyone can explain the one question I ...
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1answer
866 views

Can water exist as liquid in a vacuum chamber at room temperature?

I know boiling point at vacuum is far below the room temperature. But I still wondering if the humidity reaches the saturated humidity (100% relative humidity), will the vapor condense to liquid, ...
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3answers
963 views

Melting and freezing point

Why is the melting and freezing point of a substance are always the same ? This was quoted in my textbook but they didn't give a reason for this being so. Thank you.
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248 views

Can the laws of classical mechanics be derived from quantum mechanics? [duplicate]

Can classical mechanics be derived from quantum mechanics as the same way thermodynamics derived from statistical mechanics?
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5answers
389 views

If I replace all my lights with LEDs will my heating costs increase?

A number of nations are passing bills to phase out incandescent light bulbs. The thinking is that the tungsten filament is an inefficient method of turning electricity into light, the rest of the ...
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101 views

Rotary Steam Engine

Leon Crux invented the concept of interlocking archimedes spirals that eventually led to the scroll compressor but intended it to be used as a rotary steam engine. However technological limitations of ...
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52 views

What is the relationship between strain and electric current?

Strain or stress can be caused by different sources. I categorized theses sources as mechanical, thermal and electrical loads and formulated the total stress as follows: $$ \epsilon_{total} = ...
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1answer
136 views

Confusion in fourier's law

My book starts section 2.2 like this: Equation 1.1 is this: $$q_x=-k\frac {\partial T}{\partial x}$$ As you can see in the picture I posted, my book says that one can go from equation 1.1 to ...
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71 views

Where does the relation $u=h_f-RT+(c_p-R)(T-T_0)$ come from?

I'm working on a college project for a subject called Motorcycle Engineering, and in this project I'm supposed to do some reverse engineering on a MATLAB program to model the engine of the motorcycle. ...
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1answer
222 views

Measuring temperature at a distance

http://www.youtube.com/watch?v=gKYrXHZwtPw In this video it is explained that Land Skin Temperature (LST) are measured by NASA's Aqua and Terra satellites. It seems it works by collecting the ...
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2answers
367 views

Heating coffee by yelling?

Is it a myth that yelling to a coffee mug will heat it? I have been hearing my friend saying that screaming will heat coffee or water.
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2answers
238 views

Entropy of a naked singularity

According to the wikipedia article http://en.wikipedia.org/wiki/Naked_singularity: "Some research has suggested that if loop quantum gravity is correct, then naked singularities could exist in nature, ...
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1answer
76 views

energy efficiency, transformation from chemical to thermal energy, for district heating plants

If I have a system in which I introduce 100e.u.F (energy units) derived from chemical energy (i.e. fuel) and generate thermal energy to heat water what are e.u. absorbed by water? I.e. the efficiency ...
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1answer
841 views

Opening the fridge door to cool a room

I'm well aware that the default answer to this textbook default question is "it doesn't work", but still, I believe it does. To cool the insides of the fridge, the compressor must do work, and since ...
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6answers
677 views

What's the best strategy to fully fill the fridge with beer bottles and have them all cooled?

I'm having a party. Suppose I'd like to have a fridge full of cold ($6~^\circ\text{C}$ or below) beer bottles, in as short a time frame as possible. The fridge indicates that it is targeting (and ...
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1answer
354 views

Is the convective heat coefficient always dependent on heat flux and delta T?

I'm having a difficult discussion with a colleague because I'm running heat flow simulations for a small heater (5 mm^2 area), and I insist that if we're going to run more electrical power through the ...
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240 views

Can't understand a thing about emissivity concept

I can't understand something about emissivity. Emissivity is defined as the ratio of the radiant energy of an object, to radiant energy of blackbody at a temperature $T$. So, The vegetation has ...