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Equilibrium using Center of Buoyancy and Gravity [Problem]

I don't understand a solution to a homework question. Specifically, I don't understand the logical sequence of each bolded statement in the answer. (b) To ensure that a ship is in stable ...
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2answers
139 views

How quickly should a fluid come to hydrostatic equilibrium?

Let's say I'm holding a one-liter water bottle, full of water, which I then drop. Before dropping the water bottle, the equilibrium is for there to be a pressure gradient in the water canceling the ...
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2answers
127 views

Understanding mechanical equilibrium

In this site, mechanical equilibrium is defined as when there is no net force between the system and the boundary, it is in mechanical equilibrium. Now, what does it mean by net force? What would ...
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1answer
156 views

H-theorem and Boltzmann equation applied to Boltzmann distribution

Using the Boltzmann equation: $$ \frac{dH}{dt} = \int_0^{\infty} dr \int_0^{\infty} ds W(r,s)[p_r - p_s][\ln{p_r} - \ln{p_s}],$$ and assuming $p_r = e^{-\beta r}$, the equation looks like $$ ...
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1answer
67 views

What is the cause for mechanical equilibrium in statistical mechanics?

In classical thermodynamics, mechanical equilibrium is defined as the state of a system in which there is no net flow of volume as there should be no net pressure within the system. Ok. ...
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1answer
41 views

Is equilibrum condition consequence of second law of thermodynamics?

Equilibrum state is generally stated to be most stable state. Is equilibrium state consequence of second law of thermodynamics at microscopic level. i.e a system tends to reach the equilibrium state ...
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1answer
36 views

simple physical system involving convergence to equilibrium at decreasing speed

I want to make an analogy of an economic model (Solow 1956) with a simple physical system that exists in reality. I am not looking for a mathematical formula to describe the system (I have that ...
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1answer
48 views

Why do forces/pressures/electrons/temperatures/etc equalize

What causes various forces/etc. like to equalize? I can understand water in a tank being affected by gravity but why do high pressure systems want to move to low pressure systems (vaccuums), electrons ...
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1answer
24 views

Electrical charge equilibrium and the piezoelectric effect

About the piezoelectric effect: if I press a crystal the electrical charges segregate and an electrical voltage appears on the other two faces of the crystal. See this link for example: ...
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1answer
101 views

What happens to matter when in a thermodynamic equilibrium?

I am trying to gain a better understanding of thermodynamic equilibrium. Here's what (I think) I know: If a system is in Thermal, Radiative, Chemical, and Mechanical Equilibrium, then it is in ...
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0answers
62 views

Detailed Balance for Quantum Master Equations from System Hamiltonians with Degenerate Spectrum

Kossakowski, Andrzej, et al. ("Quantum detailed balance and KMS condition." Communications in Mathematical Physics 57.2 (1977): 97-110) gave a proof that the stationary state of a quantum dynamical ...
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0answers
35 views

Is the system in equilibrium?

If the time derivative of the Liapunov functional related to free energy of my system is zero, can I say my system is in chemical equilibrium?
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0answers
46 views

Equilibrium Points in Lagrangian Mechanics

Suppose we have a one particle system with generalized coordinates $q_i$. In classical mechanics, the corresponding Lagrangian is $L = T - V$. Assume $V(q)$ is time-independent. What additional ...
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0answers
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problem about heat in thermodynamics

$$\nabla G=-T\nabla S-T\nabla S_{sur}=-Q+q $$ $$\nabla G=-T\nabla S-T\nabla S_{sur}=-(U-W_{rew})+q $$ $$\nabla G=-T\nabla S-T\nabla S_{sur}=-(q+W-W_{rew})+q $$ $$\nabla G=-T\nabla S-T\nabla ...
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0answers
35 views

Why is it valid to assume that the liquid-vapour interface is always saturated during evaporation?

For steady state evaporation, I read from two textbooks which simply states that the partial pressure of vapour of interest (say water) at the liquid-vapour interface is equal to the saturation ...
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0answers
44 views

Vacancy Generation / Annihilation Time (Relaxation Time)

Vacancy Generation/Annihilation Time, Recombination Time and Relaxation Time ($\tau$) are all synonymously used in atomic physics literatures. They're defined as the time that it takes for vacancies ...
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0answers
54 views

Reconciling Different Vapor Pressure Definitions

In describing vapor pressure, I have often heard the following intuition: Assume a closed container that is partially filled with water. Above the water lies a vacuum. The water will vaporize until ...
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0answers
1k views

Definitions in thermodynamics: temperature, thermal equilibrium, heat

I'm currently reading Fermi's "Thermodynamics" and I'm trying to grasp the (possibly different) right definitions for temperature, thermal equilibrium, heat. To clarify, I'm looking for definitions ...
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0answers
83 views

Biological Themodynamics - What does an endpoint saturated signal mean. How does it relate to equillibrium constant

I have had a question that has been bugging me for a couple of years in my graduate school career, and I was wondering if perhaps some physicist could help explain it to me. Given an endpoint assay ...
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0answers
348 views

What is the angle of the string with the vertical?

A heavy uniform sphere of radius $a$ has a light inextensible string attached to a point on its surface. The other end of the string is fixed to a point on a rough vertical wall. The sphere ...
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0answers
21 views

Deriving the Force on an ion in the Classical Harmonic Crystal

I was following Solid State Physics by Ashcroft and Memrmin and their introduction to the Classical Theory of the Harmonic Crystal. (Chapter 22) If there are a large number of ions in a straight ...
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0answers
34 views

Number of particles in a box at thermal equalibrium

Consider a cube box of volume $V$ in thermal equilibrium at temperature $T$. We have 3 pieces of information: The probability of finding a particle of mass $m$ in the box having momentum in ...
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0answers
77 views

Coefficients of Friction in Equilibrium Ladder Problems

A problem asked me to find the the minimum angle the ladder system could have while still remaining in equilibrium: If you want to examine my reasoning: Let's take the lower end of the ladder to ...
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0answers
34 views

Boltzmann equation (Number density)

I'm trying to understand the Boltzmann equations use in the early Universe. The derivation is somewhat tedious, but in the end I end up with: $$a^{-3}\frac{d}{dt}\left(n_1a^3\right) = ...
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0answers
195 views

Ladder equilibrium problem - Where do the hinge forces go?

In my physics homework there is a problem about a hinged ladder like this and a man is standing on one of its halves. The two parts of the ladder are hinged together at the top. My question is, ...
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0answers
40 views

How to calculate the partial entropy in a fully connected ising system

I'm trying to reproduce a calculation that should lead to the partial entropy in a fully connected ising model for the high-temperature range ($\beta < 2$) in the thermodynamic Limit ($N ...
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0answers
220 views

Truss Analysis with multiple moments creates linear combinations

So in my engineering statics course we have been doing a great deal of work with trusses and machines, and a part of the physics behind it has really been confusing me. Just as a note, I also have ...
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0answers
2k views

Statics: particle mechanics versus rigid body mechanics

In particle mechanics where the notion of rotation does not apply, particles are said to be in static equilibrium when the sum of the external forces acting on the particle of interest in all ...
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0answers
22 views

Difference between equilibrium and steady state with example s

Difference between equilibrium and steady state with examples in case of charge carriers in semiconductors (difference) Reaching equilibrium or steady State