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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44 views

Multiplicity vs Partition function

I'm a little confused between all the different notations for the multiplicity and partition function. They're not the same thing, are they? I know that entropy can be expressed as $ S = k \ln\Omega ...
2
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1answer
35 views

Black plastic balls on reservoir to reduce evaporation - why black?

The story is here It states: The balls sit on top of the water and block the sunlight from hitting it, helping to reduce water evaporation as well as natural contamination and certain ...
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0answers
35 views

Is thermal and electrical conductivity correlated for all phases of matter?

After reading this interesting post about why copper is a great heat conductor, I wondered if a plasma would conduct heat better than a gas. Or, are some properties like density more important for ...
3
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1answer
77 views

Do photons have six degrees of freedom?

Calculations involving pressure and volume relationships of photon gas during the cosmologic expansion of the universe posit an adiabatic cooling process with a heat capacity ration of 4/3. This ratio ...
2
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0answers
29 views

The formula for calculating work transfer for a reversible adiabatic compression

Should we not be using Pdv for calculating the work done during a reversible adiabatic process ? Why are we using Vdp ? Can some one please explain this ? (P.S. I'm taking an introductory course on ...
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3answers
65 views

How much effect does painting a domestic radiator have?

Yes, I know it should be called a convector :-) The obvious effect is that a coat of paint, which is generally a thermal insulator, can limit the rate of heat transfer from the metal to the air. But ...
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2answers
26 views

Isothermal versus Isometric/Isochoric

My impression is that all three have something do with change in internal energy, in thermodynamics. But I cannot tell exactly their relations. First isothermal, which literally means zero ...
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2answers
84 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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3answers
2k views

Does fire have an influence on the weight of a burning object?

I know that fire is a chemical reaction, and for that reason it has no mass, but I'm not sure that this fact is enough to conclude that it has no effect on the weight of a burning object. Consider the ...
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0answers
23 views

Thermal equilibrium of simple system

Consider a system of (fermion-like) particles. The idea is to find the equilibrium state. Take 3 particles and put each of them in one of the boxes of the figure, no more than one per box. The energy ...
2
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1answer
42 views

How to compute this change of Gibbs energy for a Van der Waals gas?

The change of Gibbs energy at constant temperature and species numbers, $\Delta G$, is given by an integral $\int_{p_1}^{p_2}V\,{\mathrm d}p$. For the ideal gas law $$p\,V=n\,RT,$$ this comes down to ...
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3answers
78 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 ...
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3answers
115 views

What is the purpose of the linear approximation $\Delta L = \alpha L_0 \Delta T$?

What is the purpose of the linear approximation $\Delta L = \alpha L_0 \Delta T$? When using this, we run in all kinds of problems. For example, when a material heates up twice by 1K we get ...
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1answer
38 views

Reversible cycle approximated by Carnot cycles

My textbook, W.E. Gettys, F.J. Keller, M.J. Skove, Physics 1, gives the definition of a reversible transformation as a transformation that can be inverted by effectuating only infinitesimal changes in ...
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0answers
10 views

Is this 'combined statement' really equivalent to both the 1st and 2nd laws of thermodynamics?

Quoting from Prausnitz' Molecular Thermodynamics of Fluid Phase Equilibria, For a homogeneous, closed system ... taking into account interactions of the system with its surroundings in the form of ...
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0answers
16 views

Is lost work always positive? How to approve?

I am dealing with a question asking for comment on the sign of lost work. The case is to consider an irreversible process and a reversible process which share the same starting and ending state. Is ...
2
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0answers
15 views

Lens-Mirror systems and conservation of specific intensity

This came out of a discussion I started yesterday and a related discussion I found. I'll recap the problem quickly: Consider two blackbodies, with surface areas $A_1$ and $A_2$ and temperatures $T_1$ ...
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1answer
24 views

Adiabatic Process: Direct Formula for new Temperature and Pressure [closed]

Assume we have an ideal gas in a piston that has pressure $p_0$ volume $V_0$ and temperature $T_0$. Then we assume, that the gas is compressed to a new volume $V_1=\alpha V_0$, where $\alpha \in ...
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1answer
37 views

Paradox of potential energy of gas molecule

We know that when water is heated at its boiling point, it will become vapors. Then because there is no change in temperature, the heat supplied will be transferred to the potential energy of the ...
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2answers
64 views

Second Law of Thermodynamics and heating a blackbody with another blackbody

Given a large blackbody with surface area $A_1$ and temperature $T_1$, let's assume I can use some mirror and lens system to capture all the emitted radiation and transfer this energy to a smaller ...
0
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1answer
33 views

Newtonian heating

Suppose a fluid over a heated surface which is being stretched and the flow starts. Now the boundary condition at the surface is assumed as $q_w$ is proportional to the surface temperature. It is ...
1
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1answer
19 views

Usage of the formula Pdv for irreversible thermodynamic processes

Why do we use the formula Pdv for calculating work done in a irreversible process ? As per my knowledge , the term P indicates the pressure of the surrounding , which infinitesimally differs for the ...
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0answers
41 views

What is the physical fundamentals of Pascal's law

Pascal's law or the principle of transmission of fluid-pressure (also Pascal's Principle) is a principle in fluid mechanics that states that pressure exerted anywhere in a confined incompressible ...
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1answer
41 views

Paradox about the efficiency of a thermal engine

Based on that, the algebra calculation is correct. But it seems confused to me. Even though the overall efficiency reduces, it is still useful, isn't it? From the same amount of energy we can ...
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0answers
20 views

What are the main differences between 'Physics machine learning work' and Mainstream Machine Learning?

I have read both works from Thermodynamics of Prediction, Optimal Causal Inference and taken basic machine learning classes from computer science on prediction models, but I have yet to seen any ...
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2answers
45 views

Confusion between thermal energy and heat

In the past, I usually misunderstood that thermal energy and heat are the same. However, some materials say that thermal energy is the intrinsic value of the system, including potential energy and ...
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0answers
26 views

When can we assume a body to behave like a black body?

In an experiment I estimated the temperature of a Tungsten bulb filament measuring the resistance of it, and tried to verify whether the power of the filament is proportional to the fourth power of ...
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1answer
107 views

Why does temperature have no uncertainity?

Lets say I have an object A, with temperature $T$ and Hamiltonian $H_{A}$. Now take a thermometer B, with Hamiltonian $H_{B}$. Now when I put the thermometer in contact with A and do a measurement ...
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0answers
27 views

Can a pure vacuum with 0% gas be created? [duplicate]

If we were to create a vacuum room with no air in it to avoid air resistance can it be done?
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1answer
70 views

Calorimetry - Emitted Joules [closed]

How can one calculate the total amount of emitted joules from an object with a temperature that isn't constant? A great start is this formula: ...
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2answers
35 views

Work done of the gas

My homework is that : a container contains two half parts X and Y separated by a plate P. Part X contains ideal gas, while part Y is vacuum. Then the plate P is removed, so gas from X can spread out ...
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0answers
32 views

Vacuum pressure equivalent in a siphon hose filled with water?

So, I was thinking about how siphons worked today, and no matter how high or low the tube goes, as long as the end is lower than the start, water will flow. So, if you took a hose, ran it up 50 ...
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2answers
38 views

The quickest way to reduce an isolated system's temperature

If you are in an isolated room, having an air conditioner and a ceiling fan. What is the quickest way to cool the room. Using only the air conditioner or both of them?
0
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1answer
35 views

Why classical open system and Bose-Einstein condensate are not fundamentally the same?

The classical partition function for an open system is given as $$ Z_{\text{max}} = \sum_{N=0}^{\infty} \dfrac{h^{-N}}{N! } \prod_{j=1}^{N} \left( \sum_{i=0}^{\infty} e^{-\beta (E_{ij}-\mu)} g_{i} ...
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0answers
14 views

What does the particle to volume density physically mean for Bose-Eisenstein condensate?

The average number of particles $\langle N\rangle$ for a Bose-Eisenstein condensate in 3D is given as $$ \dfrac{\langle N\rangle}{V} = \dfrac{V^{-1}}{e^{\beta (0-\mu)}-1} + \int_{0}^{\infty} ...
8
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2answers
265 views

Internal energy of an ideal gas as a function of volume

Okay so I've been reading a bit on Thermodynamics and I found something that I couldn't wrap around my head. For an ideal gas, the change in internal energy is equal to $$\Delta U = Q + W$$ And ...
3
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1answer
131 views

Simpler derivation of sarkur-tetrode equation

Is there a reason the following derivation for the Sackur-Tetrode equation is not common? I am teaching a lower undergraduate level class and would like to derive it with simpler terms of only using ...
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0answers
57 views

Quantitative understanding of excess heat capacity in ferroics

I'm looking to understand what an excess heat capacity in a ferroelectric (FE) can correspond to qualitatively. Typically one starts with a Landau expansion of the free energy if you want to study the ...
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0answers
30 views

Room themperature over time

I am looking for a way to calculate how the temperature will change in the blue room in 1 hour. I know, that calculating the exact solution is very very difficult, as there are many factors that ...
16
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6answers
2k views

Will drinking ice cold water and eating cold food cause weight loss (over a period of time)? [closed]

A friend of mine has the idea that drinking cold water and eating cold food will assist them in losing weight. The core temperature of a human body is 37$^{\circ}$ C. If they drink water, at a ...
0
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2answers
85 views

What are the definitions of microstates and macrostates?

I have been looking up definitions for microstates and macrostates of a thermodynamic-system. I am looking for clear conditions for systems to be in the same macro- or microstate, but have had no ...
0
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1answer
64 views

How do I keep the temperature constant in a Boyle's Law experiment?

I'm trying to get a head start on our lab experiment next week about Boyle's Law. The set-up is we have an air chamber can immersed in a pot of boiling water (which is kept boiling over an electric ...
0
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2answers
41 views

How does infrared radiation increase temperature?

Temperature is proportional to the average kinetic energy of particles in a medium. When impinged by infrared radiation, what happens on the microscopic level that translates that EM wave into the ...
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3answers
31 views

Is heat conduction impeded at interfaces between dissimilar materials?

Sound in air essentially echoes off concrete walls, rather than penetrating them, because of the difference in the material properties of air and concrete. By analogy, are there pairs of solid ...
0
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1answer
59 views

Euler equation: momentum conservation in terms of enthalpy?

So I stumbled upon this equation: $\frac{\partial h v}{\partial t}= - \nabla(hv \cdot v)- \nabla P$ where $h$ is enthalpy, $v$ is fluid velocity, $t$ time, and $P$ pressure. It seems to have the ...
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0answers
31 views

Enthalpy of Isothermal Expansion [duplicate]

In an isothermal expansion, the volume of the system increases however the total internal energy and temperature remain constant. If enthalpy is the total work energy of a system, if some of the ...
0
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1answer
30 views

the final velocity non-constant acceleration

I'm not sure if my problem was asked before, but if so, a simple link to the answer would be appreciated. Basically I've recently seen videos about spud cannons that use compressed air and it got me ...
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3answers
60 views

How does the dissolution of salt affect the solution density?

Suppose you have a container of water as a solvent and you a certain amount of salt as a solute sitting at the bottom of the container that has yet to start dissolving. Supposing temperature and ...
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0answers
9 views

Humidity and ignition correlation

Does the same combustible material catch fire more readily at 50*F/100%RH or 70*F/60%RH?
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0answers
15 views

Applying conservation of energy to an ideal gas

Suppose we have cylinder which contains an ideal gas confined by a piston of mass $m$. The height of the piston is $H$, relative to the ground, and it has an initial velocity $v$, compressing the gas ...