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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2answers
58k views

How can a wooden spoon be used to prevent water from over boiling?

This is an image I found via StumbleUpon Does this actually work? If so, why?
-1
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1answer
270 views

Loschmidt's paradox - really a paradox? [duplicate]

Is Loschmidt's paradox a paradox even today? In other words, is the paradox resolved or not?
0
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2answers
341 views

Second Law of Thermodynamics, heat and quantum-level explanation

I heard somewhere that the second law of thermodynamics is stating that some heat (energy) becomes unusable for work (at the scale of the whole universe). Why is it like that? Can't heat be converted ...
2
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1answer
2k views

Do materials cool down in the vacuum of space?

Do materials cool down in the vacuum of space? If yes, how does it really work?
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0answers
57 views

upper bound for the Kelvin scale [duplicate]

Possible Duplicate: Why is there no absolute maximum temperature? On the Kelvin scale, absolute zero represents the temperature at which there is no thermal motion. Consequently, speaking ...
7
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5answers
8k views

Recommendations for Statistical Mechanics book

I learned thermodynamics and the basics of statistical mechanics but I'd like to sit through a good advanced book/books. Mainly I just want it to be thorough and to include all the math. And of course ...
2
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1answer
2k views

Heat of vaporization of water - dependence on relative humidity?

Does the heat of vaporization of water depend strongly on the relative humidity of the gas into which it evaporates? Some context: If we want to calculate the dew point of water, we find the ...
3
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3answers
265 views

What are some creative illustrations of the nature of dissipative forces?

I'm teaching a conceptual introduction to physics for American 13-15 year old students this summer. One of the main ideas I want to hit on is the relationship between energy conservation, ...
4
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1answer
647 views

Wind Turbine Impact

OK, I'm not sure this is not a silly question, but here goes. I've often wondered what the impact is of wind turbines on the weather. My question is, since wind turbines transform wind energy into ...
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1answer
1k views

Ideal gas with two kinds of particles, Grand canonical partition function

Consider an ideal gas contained in a volume V at temperature T. If all particles are identical the Grand canonical partition function can be calculated using $$Z_g(V,T,z) := \sum_{N=0}^\infty z^N ...
0
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1answer
527 views

How does the entropy of a system change when the amount of substance changes?

I am thinking of a closed system consisting only of an ideal gas. Suddenly, the amount of substance of the gas changes. No other property of the system shall change. How does this affect the entropy ...
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1answer
782 views

Which formula for entropy is correct? (OR Is the fundamental thermodynamic equality always right?)

Quick question, in the lecture notes to a thermodynamic course I'm taking, $$d\underline{S}=\frac{d\underline{U}}{T}+\Big(\frac{\partial P}{\partial T}\Big)_{\underline{V}} d\underline{V}$$ But ...
7
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1answer
818 views

Entropy increase and end of the universe

While taking thermodynamics our chemistry teacher told us that entropy is increasing in day by day (as per second law of thermodynamics), and when it reaches its maximum the end of the world will ...
4
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2answers
638 views

How can one feel cold without touching it?

Let me explain. My shower is inconsistant in how hot it gets. Whenever I turn on the shower, I always put my hand really close to the water, but not touching it, so I can feel the heat radiate from ...
3
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2answers
680 views

Heuristics for specific heat capacities of solids

A didactic question publish in The Physics Teacher (http://tpt.aapt.org/resource/1/phteah/v41/i1/p8_s1) asks which will melt more ice: 100g of metal at 100C or 100g of wood at 100C. (The particular ...
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2answers
2k views

Specific heat capacity

Which of two objects at the same tempreature can cause more intense burns when you touch it: the one with the greater specific heat capacity or the one with the smaller specific heat capacity and why? ...
3
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1answer
318 views

Wasn't the Hawking Paradox solved by Einstein?

I just watched a BBC Horizon episode where they talked about the Hawking Paradox. They mentioned a controversy about information being lost but I couldn't get my head around this. Black hole ...
1
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2answers
193 views

Using CO2 to air condition a room

I'm trying to determine how much dry ice or liquid nitrogen I would need to cool 3300 cubic feet, about 90,000 liters of air, from about 100F (37.78C or 310K) to about 90F (26.67C or 299.81K). I'm ...
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0answers
47 views

What is the fluid approximation for BCS action?

For a system with free fermion gas at finite density (i.e. free Dirac action), we have an ideal fluid description with rho, p, n. What is the fluid description for BCS action? Suppose we have a box ...
6
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2answers
1k views

What causes a Phase-Transition?

A phase transition occurs when for example, heat is applied continuously to a liquid and after a certain time it converts into a gas. How does this process work in detail? Is their a chain reaction ...
4
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2answers
226 views

Why is latent heat required?

Why is latent heat required for a system to change its state? (I.e. liquid water to ice) Why the "extra" energy?
4
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3answers
786 views

Thermodynamics of cooking rice

The question is whether (1) cooking rice in a pot of boiling water for an hour and then leaving the pot (of water and rice) to cool to room temp heats my house the same amount as compared to (2) just ...
4
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1answer
2k views

What is the meaning of pressure of a solid?

Currently I'm taking an introductory course on thermodynamics. I've got a problem with understanding what is the meaning of pressure of a solid body. The question arose when I looked at phase diagram ...
2
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1answer
256 views

Amount/flow rate of N2 needed to cool substrate

I'm trying to cool a substrate inside a vacuum chamber with liquid nitrogen. The substrate holder is a block of copper suspended from the top of the chamber via nylon screws (for thermal insulation). ...
0
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1answer
168 views

heat of a laptop when placed on a table, when placed on a pile of books and when placed on a bed [closed]

I heard somewhere that it is dangerous to place a laptop on a bed. The reason given was that placing the laptop on the bed blocks (assume that the laptop does not have sideway fans - it only has air ...
6
votes
1answer
568 views

Wick rotation and the arrow of time

It is well known that we can switch from a statistical system to a quantum mechanical system by a Wick rotation. Has this rotation some implication on the way the time flow? namely, this is an ...
3
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3answers
288 views

Slow thermal equilibrium

I have a question which is inspired by considering the light field coming off an incandescent lightbulb. As a blackbody radiation field, the light is in thermal equilibrium at temperature $T$, which ...
5
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3answers
450 views

Proof of existence of lowest temperature $0 K$

Im mathematics there is a concept of infinity meaning that whenever you pick a number and say that it is the smallest/Largest there is a way to further reduce/increase that number by ...
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1answer
2k views
0
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1answer
184 views

Is a low-current electrical arc harmful to humans?

I've heard that electrical flux non-destructive particle testing machines are considered safe because they use less than 2 amps. I have seen an arc created between two objects do considerable damage, ...
5
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1answer
1k views

Greatest volumetric heat capacity

Is there any substance with bigger volumetric heat capacity than water? According to this table water has the biggest known VHC. But I can't believe that in the 21. century we have no special material ...
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1answer
205 views

What kind of phases nanoparticles have (gas-solid-liquid)?

If a phase transition requires a number of particles that is in the TD-limit, can nanoparticles (~10 atoms) have phase transitions? What kind of phases and transitions nanoparticles have?
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3answers
433 views

How many particles is needed to observe a phase transition?

This is a question that was rised when we were discussing "what is melting actually". How many particles you need to form a liquid or solid. I have some remarks to point out what I want to know. Q: ...
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1answer
845 views

Thermodynamics, bullet fired into ice

I'm beginning to study basic thermodynamics and I want to solve this exercise: It fires a lead bullet from $3g$ to $30^oC$ with a speed of $240\frac{m}{s}$ to a block of ice at $0^0C$. How much ice ...
-2
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1answer
134 views

About heat rate and dimensions convention [closed]

Suppose I have a ceiling and its dimension are given in $Z \times C \times Y$, and a it's got a thermal conductivity $k$. Now, I want to know H, or the heat rate. It's given by $ H =\frac{kA(T_h ...
5
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1answer
346 views

Is a black hole's surface area invariant for distant intertial observers?

Let's imagine I'm very far from any massive objects, so my local space-time is Minkowskian. Off in the distance is a black hole, far enough away that it doesn't noticeably curve space-time near me, ...
3
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1answer
399 views

Boiling when I plunge my french press?

Occasionally when I make coffee in my french press I experience something odd. It happens pretty infrequently but certainly enough to be curious about. I have the grounds ready in the carafe. The ...
2
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2answers
584 views

how does heat energy start to speed up a gas molecule?

If it was possible to place a single gas molecule in a cell and freeze it to near absolute zero. What would the molecule do as it thawed out? Would it translate the heat energy into it's electrons ...
2
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0answers
99 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. ...
2
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0answers
177 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 ...
0
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2answers
9k views

Water Electrolysis Calculations

From Wikipedia (http://en.wikipedia.org/wiki/Water_electrolysis#Efficiency): The electrolysis of water requires a minimum of 237.13 kJ of electrical energy input to dissociate each mole. Each ...
2
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2answers
753 views

Ideal gas in a vessel: kinetic energy of particles hitting the vessel's wall

Reading Landau's Statistical Physics Part (3rd Edition), I am trying to calculate the answer to Chapter 39, Problem 3. You are supposed to calculate the total kinetic energy of the particles in an ...
2
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1answer
129 views

Kerr-Newman black holes and infinite charge

Recall the first law of BH thermodynamics $ dM=\frac{\kappa}{8\pi} dA + \Omega dJ + \Phi dQ $ Now, let's consider the Reissner-Nordstrom solution $J=0$ such that $m>Q$ but only slightly greater. ...
14
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2answers
30k views

What exactly is the difference between advection and convection?

After reading Wikipedia articles on advection and convection, I still cannot determine whether there is a consensus on a difference between these two terms. Sometimes, the term convection seems to ...
1
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1answer
516 views

Calculating temperature of water in the freezer

Assuming water volume ($V$), initial water temperature ($T_0$) and environment temperature ($T_e$) are known, what is the easiest way to calculate temperature of water in given time ($T$)? For the ...
2
votes
1answer
472 views

Why are turbines built differently when a change of entropy or temperature is involved?

We are talking about turbines for extraction of energy from a fluid. Consider a typical wind turbine, or a francis turbin for water - we have one hub with on set of vanes that are driven by the ...
0
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1answer
3k views

Mixing Water at Different Temperature

If I have cup of water at room temperature (say, $25^\circ$C). What would be the resultant temperature if I pour another cup of same amount of water at $100^\circ$C to it? Is it simply ...
1
vote
1answer
495 views

Efficiency of parallel and sequential heat pumps

Consider two identical heat pumps, for example, split-system air conditioners. There're two ways to make them work - in parallel or sequential. Parallel means that "hot" radiators of the machines are ...
1
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1answer
2k views

Thermal Energy from Friction on a Rope

Question: A capstan is a rotating drum or cylinder over which a rope or cord slides to provide a great amplification of the rope's tension while keeping both ends free. Since the added tension in the ...
6
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3answers
509 views

Confusion regarding entropy, reference papers request

1.a In paragraph at Wikipedia/Entropy it is stated: This is because energy supplied at a high temperature (i.e. with low entropy) tends to be more useful than the same amount of energy ...