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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8 views

increase in temperature by focoused ultrasound: magnitudes?

They use HIFU (high intensity focused ultrasound) to perform ablation of tumors. I need to know (with appropriate setup) how many watts do I need to generate ultrasound and how many degrees the ...
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1answer
33 views

Book with solved problems on thermodynamics

I am working on honing my engineering thermodynamics problem solving skills at the undergraduate and graduate level. It would be much help if you could suggest me some good books with solved ...
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2answers
2k views

Do black holes violate the first law of thermodynamics?

When a black hole absorbs matter is it destroying that mass, thereby destroying energy, therefore violating the first law of thermodynamics?
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2answers
34 views

Manometer & pressure

I have trouble with a homework question in understanding how the manometer liquid responds to pressure changes. Any help will be much appreciated. The problem goes like this: A cylinder of diameter ...
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1answer
54 views

Why do people wear black in the Middle East?

I have read various dubious explanations as to why people often wear black in the heat, from cultural to somehow encouraging the evaporation of sweat (unconvincing). So, does anyone know what, if any ...
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0answers
19 views

how much heat will be produced when air is compressed to liquid air [on hold]

I understand about 700 litres of ambient air becomes 1 litre of liquid air. I want to know how much heat will be dissipated when this happens. I appreciate any help.
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0answers
17 views

Why do high altitudes have larger diurnal temperature variation than lower altitudes?

It seems like the lack of atmosphere should not be playing a role in the diurnal temperature variation because that's what makes it colder. Mountains are not that dry, usually.
56
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1answer
3k views

Where is the flaw in this machine that decreases the entropy of a closed system?

I was thinking about a completely unrelated problem (Quantum Field Theory Peskin & Schroeder kind of unrelated!) when the diagram below sprang into my mind for no apparent reason. After some ...
5
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1answer
61 views

Would neutronium emit heat?

Since accelerating a charge creates EM radiation, and there are no charges in neutrons to be accelerated, would that mean neutronium emits no radiation? Consequently, to preserve the second law of ...
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0answers
34 views

Final temperature of water+ice+water Mix [on hold]

I found this physics question: In a container there is a mixture of water at $ T = 0°C$, mass $m_w = 300g$, and ice, mass $m_i = 600g$. More water is added into the container, mass $m = 1100g$ at ...
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1answer
23 views

Body that both cools (proportionally to temperature difference) and heats with constant power

This is almost more of a math question, and a simple one, but I can't figure it out, and I haven't been able to find a solution online since I don't really know what words to search for. There is a ...
0
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1answer
60 views

Why does a cloud form around ice cream?

Everyone have probably seen the phenomenon as one opens a cool ice cream from its pack, a white cloud begins to flow around the ice cream surface, and it constantly spreads out until the ice cream ...
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1answer
34 views

Melamine dish cools beyond ambient temperature

I have observed a phenomenon that I find hard to understand. A plastic, melamine like dish is filled with food (spaghetti, chile, soup, etc.) The dish and food is heated in a normal microwave oven ...
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0answers
25 views

Will water vapour rise in vacuum?

If I put water vapour in vacuum, will it behave normally like a gas? Will it rise up in the vacuum?
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0answers
19 views

Best thermal (heat) radiation barrier (insulator)? [on hold]

Which material provides best insulation from thermal (heat) radiations? In other words, which material blocks most of heat radiation from escaping?
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0answers
28 views

Boundary conditions for a radiative heat transfer problem [on hold]

Consider the heat equation $$ \frac{\partial T}{\partial t} - a\Delta T + \mathbf v \cdot \nabla T = S $$ where $S$ is a source term dependent of the radiation intensity $I$ and the temperature $T$. ...
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1answer
59 views

Why is the entropy of most systems not infinite?

We can define a microstates as follows: Definition 1: A complete specification of the six coordinates of each molecule of a system, within the limits of the dimensions of the cell in which its ...
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0answers
24 views

Storing ice for HVAC

Apologies if this question is outside of the scope of the site. Assume my home is a $20 \textrm{ ft} \times 40 \textrm{ ft} \times 10 \textrm{ ft}$ block. Further assume that it has continuous ...
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2answers
53 views

$ \Delta H = C_p \Delta T $

The definition of enthalpy as a function of heat capacity and temperature change. $ \Delta H = C_p \Delta T $. Does it only apply at constant pressure? In my discussions on this board and also with ...
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1answer
13 views

why we use Gibb's free energy concept in Ehrenfest's theory of Phase transformation?

Why do we use the concept of Gibbs's free energy in Ehrenfest's theory of phase transformation ? Why don't we use Helmholtz free energy concept?
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1answer
19 views

Equipartition Theory at room temperature.

I read a statement about participation theory. The equipartition theorem is generally valid only at high temper- ature, so that the thermal energy is larger than the energy gap between ...
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0answers
12 views

chemical thermodynamic [on hold]

Calculate U and H for each of the following changes in state of 2.50 mol of a perfect monatomic gas with CV,m 1.5R for all temperatures: (a) (1.50 atm, 400 K) → (3.00 atm, 600 K); (b) (2.50 atm, 20.0 ...
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2answers
32 views

Temperature rise during friction

Why the temperature increase when the load increase during friction ? Why the temperature increase when the contract time increase during friction?
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1answer
13 views

What the effect of thermal diffusivity on temperature rise during friction

If we have two material in friction wich metal will produce the temperature?the metal with lower diffusivity or with higher diffusivity will be the source of temperature
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1answer
106 views
+50

Dr. Pierre-Marie Robitaille: On the Validity of Kirchhoff's Law

Lately I've been researching about the black-body spectrum and the historical development of Planck's Law. I mainly wanted to understand a little bit more why many different objects (Stars, Hot ...
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1answer
42 views

Temperature increase during friction

There is pin made of Asbestos and two disc material Aluminum and steel in first experiment i used Aluminum disc with asbestos pin in wear test the disc is rotating and the asbestos was in frictional ...
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1answer
32 views

Emulating changes in building temperature

I need to emulate what happens to the temperature in a building when turning the heating on and off, for a kind of computer simulation. I don't even know where to start, so I hope you can help me out. ...
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1answer
31 views

Why the air is more compressed near to the ground

I'm studying the adiabatic effect of the air on the atmosphere but i can't understand why the compression near to the ground is higher, is something relate to the higher pressure caused by the earth ...
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0answers
10 views

Range of thermocouples

Why do thermocouples have a restricted range of temperature that can measure, say for example some go from –200 °C to +268 °C, what makes them to be useless below or above?, I know above may become ...
3
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1answer
62 views

Is the MaxEnt “interpretation” of statistical mechanics the current mainstream approach?

I've only recently started studying statistical mechanics and I'm quite confused with the MaxEnt and anti-MaxEnt ideas. I'm looking for a concise answer, if it is possible, not really a description ...
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1answer
30 views

How to reduce cooling time of hot aluminum casting / block? [on hold]

I am doing project on "reduction of cooling time of hot Aluminium casting/block". Aluminum casting / block temperature is 250degree C (532 K), size diameter 600mm x 150mm and weight 25kg. In order ...
0
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0answers
25 views

entropy balance equation in thermodynamics [closed]

can any body help me to prove the following entropy balance equation. \begin{equation} T \frac{ds}{dt}=- div \mathbf{q} \end{equation} where $T$ is absolute temperature and $s$ is entropy $\mathbf{q}$ ...
0
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1answer
28 views

Thermal expansion of metal spring

I am attempting to figure out why a laser layout tool I have is drifting over time. It was designed with a small adjustment mechanism that relies on a spring to apply pressure to a fulcrum that ...
0
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0answers
30 views

change in free energy at natural state

I am styding a book on thermoelasticity, here free energy $f(e_{ij},T)$ is expended into taylor series in the vicinity of the natural state (when $e_{ij}=0$,$T=T_0$) and entropy s such that ...
2
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0answers
27 views

What is the pressure of a charged gas?

I have $N$ ${\rm H}^+$ gas molecules in a sealed, electrically insulated container. What equation can I use to accurately calculate the pressure of the gas? It seems to me that $PV = nRT$ will not ...
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1answer
61 views

What ice pack formula can hold the largest energy difference?

I recently bought some Freez Pak brand ice packs. The label advertises: "Colder Than Ice". I realize now that it's just a stupid marketing claim, but at first, it got me wondering if they had some ...
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0answers
20 views

Adiabatic Surfaces in thermodynamics

In some lecture notes on thermodynamics there is a discussion as to whether by assuming the first law of thermodynamics alone we can prove the existence of a adiabatic surface in three dimensions. To ...
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0answers
14 views

What is the relation between scattering amplitudes, fluctuations, response functions and correlations in macroscopic equilibrium systems?

In Kardar's book Statistical Physics of Fields, he mentions that that correlations at different length scales can be measured by scattering. If its electric correlations, you would scatter light and ...
2
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1answer
57 views

Is the $\mu VE$ ensemble possible to formulate?

I have recently learned about ensembles in statistical mechanics, and I've seen multiple applications and interpretations of the EVN (microcanonical), TVN (canonical), $\mu$VT (grand canonical) and ...
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0answers
52 views

How to make two equations dimensionless? [closed]

I recently got set this problem and am having trouble scaling the resulting equations. Any help would be appreciated. An incompressible thermal conducting fluid is contained between two infinite ...
0
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1answer
50 views

Fermi Level: chemical potential vs. electrochemical potential

In solid-state physics it is understood that the Fermi-Level is the electrochemical potential. The Fermi-Level is defined to: However, in thermodynamics this formula is referred to as the ...
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0answers
16 views

Application of surface tension in thermodynamics [closed]

I'm writing a paper about surface tension, and have problems with finding literature about application of surface tension in measuring some thermodynamics quantities. Can you help me? Thank you
1
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1answer
38 views

Entropy reversal in magnets

Entropy is an irreversible phenomenon without any energy supplied to reverse it. I was reading about paramagnetic substances and how dipoles align inside them on application of magnetic field. My ...
1
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1answer
43 views

Why is Cv used in the adiabatic expansion of Carnot Cycle to calculate internal energy

When I took this class years ago, I simply accepted it as fact. However, now that I'm teaching it, the following bugs me....a lot. Why do they use Cv to describe the change of internal energy during ...
0
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1answer
40 views

Open systems (Conservation of Energy): is a temperature change possible if a tube is thermally isolated?

Full question: consider an perfectly thermally isolated cylinder. Water is flowing through this cylinder from the entry to the exit. Is it possible for the water flowing through the exit to have a ...
0
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2answers
43 views

Removal of heat from a closed system using electricity

I was thinking this morning about how heat could be removed from a system in such a way that it is stored for future use. My ideas are a form of thermo-electric system that converts heat into ...
-3
votes
1answer
92 views

Can someone explain about M-theory? [closed]

Can someone explain about M-theory? I am very new to M-theory and string theory. I am very through with classical physics and little bits of quantum mechanics. Will you be able to explain why ...
-1
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2answers
55 views

If heat can't be transformed into other forms of entropy, why do hot things radiate electromagnetic waves?

The laws of entropy says entropy can only increase. On the other hand, if I take a hot object, it will naturally convert its heat into EM radiation. How is this possible? Does EM radiation count as ...
2
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0answers
52 views

Flow between two infinite plates [closed]

I recently got set this problem and I was wondering if anyone would be able to give me some hints/intuition on how to solve it. Thanks. An incompressible thermal conducting fluid is contained between ...
0
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3answers
79 views

What is the relationship between entropy and work? [closed]

Can someone explain the relationship between entropy and work? I've been reading my textbook and looking online but I feel like I'm missing something. Can someone explain it in layman's terms :)