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3
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2answers
854 views

Why can't charge be in a stable equilibrium in electrostatic field?

I am reading Feynman's Lectures volume_II where he discussed the impossibility of the presence of stable equilibrium in an electrostatic field. There are no points of stable equilibrium in any ...
0
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2answers
58 views

Angles in a static equilibrium

I have three masses (Fα, Fβ & Fg) with 2 pulleys, and a wind variable which is in static equilibrium. I have already calculated the appropriate forces for the 3 masses by multiplying it with 9.81m/...
0
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2answers
111 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 ...
6
votes
1answer
114 views

Adiabatic piston: why is Callen's argument flawed?

This question is related to this one. I would ask you to read that question and my answer to the question itself before answering this one. The problem is the following. In his book Thermodynamics, ...
1
vote
1answer
65 views

Functions of state and definition of equilibrium

Consider this - A function of state is any physical quantity that has a well-defined value for each equilibrium state of the system. (Blundell and Blundell - Thermal Physics) My question is - Are ...
1
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1answer
151 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. ...
0
votes
1answer
40 views

How does distance affect force?

In the image below, the system is in equilibrium. Some force is applied at the bottom of the vertical pole and is being opposed by some force at the top by the horizontal pole... But I feel as though ...
0
votes
1answer
74 views

A counterexample to the Law of Stable Equilibrium?

This is the "Law of Stable Equilibrium", according to Hatsopoulos and Keenan: A system having specified allowed states and an upper bound in volume can reach from any given state one and only ...
0
votes
1answer
59 views

Mechanical equivalent of heat => transfer from work W to heat Q

Consider the following experiment to determine the mechanical equivalent of heat $\mu = \frac{\Delta W}{\Delta Q}$ Not seen in the picture is a weight with known mass hanging down the cord. When you ...
0
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1answer
59 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 ...
0
votes
1answer
75 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: http://www....
0
votes
1answer
135 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 ...
5
votes
0answers
103 views
+50

Computational scaling of quantum and classical Monte Carlo algorithms

How does the computational complexity of finding an equilibrium thermal state for a given Hamiltonian at a given temperature scale with system size under classical and quantum Monte Carlo? I know ...
5
votes
0answers
155 views

Thermodynamic equilibrium or thermal equilibrium and equipartition theorem

In all derivations of the equipartition theorem I can find a thermodynamic equilibrium distribution is used to show it's validity. But more vague sources (physics.stackexchange answer by Luboš Motl, ...
3
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0answers
39 views

Timescales of physical and chemical equilibrium

Background When describing the behaviour of a reacting systems, we usually don't hesitate to apply property models to relate the local properties of each species. For example, in the case of a gas ...
3
votes
0answers
128 views

Le Chatelier's principle and energy minimization

In Callen's "Thermodynamics" in section 8.5 he asks us to imagine some perturbation $dX$ of an extensive parameter of a system in contact with a reservoir that acts to hold fixed the intensive ...
3
votes
0answers
78 views

Is it possible to have a line rather than a point where the three states of a substance can exist?

Most of us are familiar with state diagrams that define which of the three states a substance will take given the pressure and temperature. And that some substances, such as water for example, exhibit ...
2
votes
0answers
142 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 ...
1
vote
0answers
42 views

Are these torques correct for a simple balancing/fulcrum experiment?

For my physics lab, they had us do a simple static equilibrium experiment where we rested a ruler on a fulcrum (at its center of mass) and then attached varying amounts of weight on either end at ...
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0answers
38 views

Thermodynamic derivation of condition for equilibrium of triple line

Edit:(4/1/2016) Okay, I get how the required equation arises from force balance. All forces are acting on the same length, so the length cancels out of the equation and what we've got is essentially ...
1
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0answers
48 views

Why dynamic equilibrium exists?

We know that at equilibrium Gibbs energy is minimum. We also know that at equilibrium both forward and reverse reactions occur simultaneously, and also we know that for a reaction to be spontaneous ...
1
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0answers
63 views

In an equilibrium of two systems, why is not true that $\frac{\delta S_{1}}{\delta N_{1}} = \frac{\delta S_{2}}{\delta N_{2}}$?

Why is not true that $\frac{\delta S_{1}}{\delta N_{1}} = \frac{\delta S_{2}}{\delta N_{2}}$ across two systems that exchange particles? It is true, instead, that $\frac{\delta F_{1}}{\delta N_{1}} = ...
1
vote
0answers
48 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?
1
vote
0answers
151 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
44 views

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 ...
1
vote
0answers
84 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 ...
1
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0answers
68 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 ...
1
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0answers
65 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 ...
1
vote
0answers
2k 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 ...
1
vote
0answers
114 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 ...
1
vote
0answers
622 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 rests ...
0
votes
0answers
16 views

Easiest way to levitate a ferromagnetic material that is not a permanent magnet?

I want to levitate an iron cube that is not a polarized permanent magnet. What is the easiest way to do this?
0
votes
0answers
23 views

Can a diamagnetic levitator levitate non-permanent ferromagnetic materials?

I am building a diamagnetic levitator that will eventually levitate a small neodymium cube. However, is it also possible for an iron cube to be levitated as well? I know that diamagnetic materials ...
0
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0answers
22 views

How is equilibrium achieved when masses are unbalanced?

Consider the see-saw scenario shown below (This image was from a Phet simulation) If you place a 5kg mass 0.25m from the pivot point, the seesaw will have net torque in an anticlockwise direction, ...
0
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0answers
32 views

In stochastic thermodynamics, can you define the notion of equilibrium for microstates/individual trajectories?

Recently there has been quite some research on interpreting statistical thermodynamical quantities at the level of microstates/individual trajectories. Although I did not find any interpretation/...
0
votes
0answers
29 views

Finding pressure as a function of height from centre

How do you find the pressure as a function of height from the centre(geometric) of any rigid body (hollow) of negligible mass when it contains a fluid of density D filled completely and is static, ...
0
votes
0answers
43 views

Point of zero gravity for fixed masses?

Given a number of fixed point masses in 3D space, is there necessarily one or more points where there is zero gravity (ie, the combined gravity of the masses cancels out), and, if so, how do I find ...
0
votes
0answers
159 views

Thermal state vs equibilibrium state

Could someone explain what's the difference between a thermal state and an equilibrium state? Or is it even the same?
0
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0answers
60 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 line,...