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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Negative temperature thermodynamics

I asked this question about thermodynamics. I considered $$T=\frac{\partial U}{\partial S}$$ at constant $V$ and $N$ (number of particles), but now I can't figure out the change of $U$ with respect ...
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520 views

Where does the joules come from (ideal gas constant)?

I have not done any physics in ages and have recently started studying it. The first chapter in my book deals with the ideal gas constant: $$pV=nRT$$ It is rewritten as: $$R=\frac{pV}{nT}$$ When I ...
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1answer
32 views

Is the equilibrium state in thermodynamics a consequence of the second law of thermodynamics?

Is the thermal equilibrium state the state of maximum entropy? Is it a consequence of the second law of thermodynamics?
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51 views

Human body emits Radiation [closed]

Human being emits which type of waves and how to find that waves any possibility to detect this waves by Using sensors
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33 views

I need to remove water from a system [closed]

I work in an industry and I need to remove water from a system. The scenario: There is a washer and a blower on a conveyor belt. The item being washed is plastic (not sure what type) and can't be ...
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31 views

How can we describe or model the spread of ice during the freezing of the surface of a still lake?

Premise: I live in a place where it is unquestionably wintertime in every aspect of the phrase. I was driving down the street and I drove by a lake. There was a recent and sudden temperature drop ...
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58 views

Can kinetic energy in atoms result in emission of all types of EM radiation?

I already know the fact that when solid objects heat up, they emit thermal energy which is also known as infrared radiation. However, if the atoms in that solid were to begin gaining more or less ...
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16 views

Are all partial molar properties defined as a derivative at constant T,P?

Are all partial molar properties defined as a derivative at constant T,P? Are molar derivatives at constant T,V or S,P or S,P of any use? Is there a reason for that or mere convention?
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57 views

What makes a thermodynamic canonical variable canonical?

The last paragraph of page 1352 of IUPAC Technical Report Use of Legendre transforms in chemical thermodynamics" (Alberty, R.A., Pure Appl. Chem., Vol. 73, No. 8, pp. 1349–1380, 2001) says that ...
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1answer
71 views

Thermodynamics - internal energy

What would the curve that describes the change of internal energy ($U$) with the volume ($V$) be like if the change in the temperature is negative? My try: For a ideal monoatomic gas, we have ...
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1answer
51 views

How is heat and temperature related? How will a thermometer react in the following conditions? [closed]

Consider the cooking stove and LPG fuel for example, all my questions will be related to it. Assume I have a frying pan made of steel which is kept on the the stove with the knob set to moderate. ...
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1answer
34 views

Closed system, gas change in time

I'm trying to find out how to determine how a pressure of gas changes in time, but I can't find a way. I have a system with constant volume $V$ (closed system, exchanges heat with environment through ...
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17 views

Heating water with low and high gas heat

Similar type question is asked before but i'm looking for other aspect of it. I observed that if water is heated with low gas heat, it takes long time but it retains it high temperature for long time ...
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4answers
169 views

More detail on why pressure increases at the bottom of a column of gas

The question Why does the air pressure at the surface of the earth exactly equal the weight of the entire air column above it asks why the air pressure at any elevation is equal to the weight of the ...
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1answer
54 views

Why aren't (domestic) kettles insulated?

In my experience of buying and using kettles, I have come across none which are insulated. The obvious reasons as to why it would be beneficial being that heating time would be reduced, similarly, ...
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76 views

What's the physical meaning of the integral of the squared temperature in a one-dimensional rod, used to prove uniqueness of soln. in heat eqn.?

Before getting to the question, some background. Let $u(x,t)$ be the temperature in a laterally insulated rod of length $L$, at position $x$ and time $t$. The temperature satisfies the heat equation ...
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2answers
116 views

What is the difference between classical thermodynamics and statistical mechanics? [duplicate]

What is the difference between classical thermodynamics and statistical mechanics? To me, they are greatly different but are different approaches for explaining same thing. But I do prefer ...
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1answer
39 views

Equivalence of different definitions for chemical potential

In some books, the chemical potential is defined in term of the Gibbs energy as $$ \mu_i \equiv \left( \frac{\partial G}{\partial n_i} \right)_{P,T,n_j} $$ where $n_j$ indicates all mole numbers ...
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2answers
72 views

What is the solution for the apparent contradiction of Second law due to energy fluctuation?

A system has maximum entropy when it has reached thermal equilibrium. But as statistical mechanics say, there is always an otherwise infinitesimal probability of particles to confine at a corner of ...
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28 views

Effects of pressure rate of change on the temperature of a fixed amount of gas

In Vol I,Chap 1-2 of the Feynman lectures on Physics,Feynman talks about how a change in pressure of a fixed amount of gas enclosed in a piston can cause its temperature to increase/decrease. He ...
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2answers
76 views

How can there be any probability of finding the molecules clustered in half of the box,the other being empty?

Suppose,there are six molecules(indistinguishable) constantly jostling around in a box. The central configuration is when there are $3$ molecules in either halves of the box and having probability ...
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1answer
77 views

Flakes of Ice in Frozen Milk and Orange Juice

When I was a kid, my family used to put our gallon jugs of milk and orange juice into the freezer when we'd go away on vacation so that they would keep longer. As I remember it, if we were gone for a ...
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2answers
52 views

Magnons contribution to spontaneous magnetization

In Statistical Physics part II of Landau's course in theoretical physics it is stated that the magnon part of the spontaneous magnetization can be calculated as $$ M_m \equiv M(T) - M(0) = ...
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1answer
55 views

Meaning of reversibility and quasistatic processes

A process in a closed system is reversible if the entropy change is $dS = \frac{dQ}{T}$. A process is quasistatic if a process is infinitely slowly. Now, if a process is reversible, this means ...
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1answer
64 views

Relation between isentropic/isenthalpic to adiabatic?

We have $dQ = T dS$. Does this imply that a process is adiabatic $dQ = 0$ if and only if it is isentropic $dS = 0$ for any process? This does not sound right, as this would mean that there is no ...
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1answer
68 views

How can I estimate the cooking time of a roast?

I never remember what worked before, or to write it down someplace. In any case the size and starting temperature will vary. The instructions I learned from refuse to give a time at all, and the ...
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3answers
758 views

Would a perfectly clean and perfectly smooth champagne glass have no bubbles?

My understanding is that nucleation sites for bubbles in a champagne glass are either due to defects in the glass or due to fibers in the glass. (See this article for details on that statement.) Does ...
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1answer
59 views

What is the interpretation of pressure times volume as energy?

I know that pressure times volume has units of energy, but is there an intuitive explanation of how the pressure contributes to the total energy? It seems clear for ideal gases using the $PV=nRT$ ...
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35 views

Derivation of thermodynamic temperature

In deriving thermodynamic temperature scale, it uses the concept that heat transfer between two reservoirs is the function of the reservoirs' temperatures. i.e. Q1/Q2=$Φ(T_1,T_2)$. And then further ...
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2answers
80 views

Thermal Equilibrium and Canonical Ensemble

1 - Are two closed systems (with fixed volumes and of the same gas) in thermal equilibrium equivalent to two isolated systems at the same temperature? 2 - In the canonical ensemble, the "small ...
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1answer
21 views

Is the ratio of heat transfers always given by the same function?

In deriving the thermodynamic temperature scale, it uses the concept that heat transfer between two reservoirs is the function of the reservoirs' temperatures. i.e. $\frac{Q_1}{Q_2}=Φ(T_1,T_2)$. And ...
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1answer
165 views

What is the fastest way to heat my car?

During the winter months I often have to drive in a cold car and I want to warm up as fast as possible. What is the best setting to put the air on in order to warm up the entire cabin in the least ...
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3answers
291 views

How to work out the relation between the “mean relative speed” and the “mean speed”?

I'm a freshman and am taking the general physics course. I just learned intro thermodynamics. One problem that really puzzles me is the calculation of "collision mean-free path", where calculating the ...
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1answer
40 views

How does energy flow between two parts of the system that are in thermal equilibrium?

As said by Peter Atkins, Though two bodies are in thermal equilibrium,energy always flows in both direction, but the net energy is zero. Now, how does it take place? I know the macrostate ...
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30 views

difference between Heat and temperature [duplicate]

Temperature is often said to be average kinetic energy of the atoms and heat the sum of kinetic energy of all atoms. I dont agree with this definition of Heat as Heat is NOT energy. It is mode of ...
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2answers
2k views

Which ball falls faster, the cool one or the hot one?

Suppose we're on the top of the Tower of Pisa (or a larger version of it) with two identical cannonballs. We heat one up (say, to 200 degrees Celsius, or some other high temperature before it starts ...
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Does Noether's theorem apply to entropy?

Entropy appears to have a translation symmetry - adding some constant value to it doesn't appear to my fairly rudimentary understanding of physics alter the actual physics. Is this correct? Now ...
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1answer
58 views

How to move liquid uphill against a thermal gradient, without moving parts

I am looking for a conceptual way of dealing with the following. I am not looking for a set of blueprints. Consider a 5 meter x 10 cm vertical closed tube filled with a substance in the gas and ...
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2answers
39 views

How to find the initial temperature? [closed]

I am stuck in the given problem hope u can help me: Some hot water was added to three times its mass of water at 100 C and the resulting temperature was 200 C. What was the temperature of the hot ...
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Calculation of Water Temperature

In a close looped process the soft water (approx. $200\frac{m^3}{h}$ at $14$ barg) gets heated gradually from the ambient temperature to $\Delta$T of 20°C in $13-14$ minutes, i.e. if amb. temp is 45°C ...
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1answer
65 views

What is dynamic equilibrium actually?

Recently I have asked question sort of like that: Is thermodynamic equilibrium static or dynamic ? But then I wanted to realize what actually a dynamic equilibrium is. I read the wiki article, ...
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1answer
74 views

Definition of Entropy for reversible and irreversible process

$\int \dfrac{\delta Q}{T}$ can't be used to calculate entropy of an irreversible process. If you happen to know heat supplied and temperature at which it is supplied for just an instant. Can you then ...
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2answers
66 views

Is there a portable method of preventing all IR radiation from being emitted?

Me and some friends were recently disuccing "How cool it would be to be invisible", from a military viewpoint, I said that Camouflage, when done correctly, works surprisingly well, so invisibility was ...
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1answer
58 views

Efficiency larger than one?

The efficiency of a heat engine is the work we can do divided by the heat we take out of the hot reservoir. This quantity is always $ \le 1$. The efficiency of a heat pump is the heat we can release ...
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2answers
67 views

Heating of two identical balls [closed]

You are given two identical steel balls of radius (say) 5 cm. One ball is resting on a table, the other ball is hanging from a string. Both balls are heated (with a blow torch) until their radii have ...
3
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3answers
66 views

Entropy of loops in the PV plane

The change in entropy of the Carnot and reversible cycles is said to be 0. Several other loops are supposed to have a non-negative change in entropy. This presents 2 problems which I cannot ...
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2answers
71 views

Thermodynamic equilibrium of an isolated system

When an arbitrary system is isolated and left to itself, its property will in general change in time. ....after a sufficiently long time,the temperature will become the same at all points and then ...
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2answers
12 views

Exothermic heat release mechanism in gases

How is heat released when bond formation occurs in gases? For example, when atomic oxygen and molecular oxygen combine to form ozone?
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1answer
36 views

How are specific volumes accurately measured experimentally?

In every thermodynamics textbook there are tables containing the specific volume of various fluids at different temperatures and pressures. My question is, how is this data obtained experimentally? ...
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73 views

Is Boltzmann distribution contradicting with the fundamental assumption of statistical thermodynamics?

In equilibrium statistical physics the fundamental assumption of statistical thermodynamics states that the occupation of any microstate is equally probable (i.e. $p_i=1/\Omega, S=-k_B\sum p_i\,{\rm ...