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Questions tagged [equilibrium]

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Why can an object not be pulled beyond the polygon which is forming from the attachment points?

I am looking for the physical equations that explains why a 2D object on a 2D surface, e.g. a rectangle cannot be pulled further than the greatest/smallest x/y coordinates of the points it is attached ...
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1answer
60 views

Is mechanical equilibrium assumed while finding the equation of state in thermodynamics?

The mechanical equilibrium is a state in which the pressure (and elastic stress) inside a gas is evenly distributed. Do we make such an assumption while deriving the equation of state in ...
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1answer
306 views

Why is the helmholtz free energy minimized?

I don't quite understand the principle of minimum energy despite having read the derivation on Wikipedia. I think I got lost when the free energy was defined as $A= \max_S{\left(U-TS\right)}$, ...
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1answer
78 views

is semiconductor in thermal equilibrium?

If a semiconductor is heated such that there is no temperature gradient, is it under thermal equilibrium? I have studied that if no temperature gradient exists across a semiconductor then it's in ...
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1answer
394 views

The set up for attaining triple point of water

How to realize the triple point of water? My question is more or less the same as the one in the link above but with one added doubt. The answer claims that pressure will adjust itself so as to stay ...
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1answer
627 views

What is the difference between vapor and liquid with same temperature?

When the temperature is same, it means that the kinetic energy of the particles of both phases are the same, so what is the difference between a vapor and liquid of a substance, such as ethanol, when ...
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0answers
91 views

Why does the Rayleigh-Taylor instability growth rate increase with wave number?

It can be easily derived that the Rayleigh-Taylor instability growth rate on the boundary of two fluids (i.e. denser fluid supported by a lighter fluid) under gravity, $g$, is given by $gk\eta$, where ...
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1answer
66 views

Physical intuition for the Dirichlet problem

I'm studying complex analysis right now, and I am reading about the Dirichlet problem in Greene and Krantz's book Function Theory of One Complex Variable. In Chapter 7, Section 7, the authors mention ...
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2answers
82 views

Are interactions with the environment unnecessary to attain thermodynamic equilibrium?

First of all I apologize for the lenght of this question. I have some basic statistical mechanics facts that I am confused about, and in this subject it is probably better to be precise. When ...
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0answers
146 views

What are some good articles on trend to equilibrium?

I am interested in studying systems out of equilibrium that are trending to equilibrium. Trend to equilibrium, entropy production, etc. seem to be very tricky topics. Any suggestions will be ...
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2answers
80 views

If the torque caused by a force is cancelled out, is the force cancelled out as well?

I calculated the value of $\theta$ to be $53^{\circ}$ for (ii) by using the principle of moments ($6\sin\theta r 2 = 2.4 r$ ) as the disc is in equilibrium. Nothing wrong so far. For (iii), I ...
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208 views

Heat transfer in the isothermal expansion in the Carnot cycle

Problem In the Carnot cycle there are two adiabatic and two isothermal processes. This question focuses on the isothermal expansion. In the isothermal expansion books often writes that the system is ...
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1answer
208 views

Pivoted Rod Problem [closed]

Hi this question popped up on AP Physics C practice test, and I keep on getting T = mg/2 through equilibrium. I got the torque from gravity is mgsinthetaR/2 and the torque from the Wire is TsinthetaR, ...
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2answers
153 views

Is the rate of evaporation in the below mentioned situation constant when liquid vapour equilibrium is not reached?

i am studying liquid vapour equilibrium and there is the set up (below) for the experiment.The conditions:temperature is constant throughout. in this case is the rate of evaporation of the liquid ...
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1answer
508 views

Static equilibrium- when do you use forces and when do you use torques?

I'm working on an answered physics question in the book but I'm having trouble understanding why the problem could be solved by setting net torque equal to 0 and not net force. You are asked to find ...
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Dilemma of classical physics: stationary particles that can't be in stable equilibrium

Statement from Electricity and Magnetism (Edward Purcell): $$U = −0.8738Ne^2 /4π\epsilon_0 a$$ The negative sign shows that work would have to be done to take the crystal apart into ions. In ...
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1answer
92 views

Are all thermodynamics potentials minimized at thermodynamics equilibrium?

It is said that all thermodynamics potentials are equivalent. Some are more useful than others to describe some systems, based on which state variables are kept constant and which are allowed to vary. ...
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1answer
246 views

Laws of Motion: A man pushing an immovable wall [closed]

If a man pushes an immovable, rigid wall while standing on rough ground, would the man be in equilibrium? Here's my attempt: The man would be in equilibrium in the vertical direction, since ...
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1answer
241 views

Has the zeroth law of thermodynamics ever been proven?

Has the zeroth law of thermodynamics ever been proven? I know the zeroth law of thermodynamics probably follows from the second law of thermodynamics but according to The statistical nature of the 2nd ...
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1answer
127 views

If photon decoupling was a departure from equilibrium why does CMB exhibit a blackbody spectrum?

Decoupling of photons from the cosmic plasma or thermal bath is said to be a point of departure from thermal equilibrium. But we know that the cosmic microwave background (CMB), consisting of the ...
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1answer
85 views

Extent of reaction vs driving force

For an endothermic reaction with a negative change in entropy, based on dG = dH - TdS increasing the temperature should make the process "less spontaneous". However, if the reaction is endothermic ...
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1answer
78 views

Problems with understanding conductors in electrostatic equilibrium

I watched a few videos on conductors in electrostatic equilibrium and all I understood is that the charges stick to the surface of the conductor. So does that mean if I have a copper wire with no ...
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1answer
170 views

Proof of Thomson's theorem on electrostatics using variational calculus

I'm following a proof of Thomson's theorem but I'm a bit confused when they use a lagrange multiplier to include the charge conservation constraint, could someone explain to me how is this multiplier ...
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1answer
314 views

Nonsensical equation for slipping vs. tipping point on an incline?

Question Imagine a block is resting on a ramp that is inclined at $\theta$. We push the block with a force $F_\text{push}$ directed down the ramp. The magnitude of the force $F_\text{push}$ is ...
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1answer
231 views

Relation between ergodic hypothesis and fundamental postulate of statistical mechanics?

The fundamental postulate states, roughly, that each microstate of a system consistent with certain known constraints (e.g. on the total energy of the system), is equally likely to occur. The ...
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2answers
88 views

Can we take rotational equilibrium of only one part of a body?

Can we take rotational equilibrium of only one part of a body? Such as in a step ladder, where BD is a rope. Can we take rotational equilibrium of AC about C, and not the full ladder?
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57 views

How is equilibrium possible here? (motor + linkage)

During my engineering course we were discussing systems in equilibrium and I came up with a situation that I don't understand. Say we have an electric motor which drives a linkage consisting of 'disc ...
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2answers
961 views

How does a balancing toy work?

I know that the balancing toys have their center of mass under the axis on which they are balancing. That's why they stay still. But when we give a little tap on it, it re-balance itself. But how does ...
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2answers
135 views

Clarification about Thermodynamic Equilibrium

Let’s say that we have a big sphere filled with gas, and in its center a solid core of a very dense material. The sphere is in equilibrium, alone in space. Because of the gravity of the core the gas ...
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0answers
159 views

Is there any example of a real-life system which violates the “third law” of thermodynamics while remaining at equilibrium?

I assume the following statement for the "third law" of thermodynamics: $$\lim_{N \to \infty} \lim_{T \to 0} \frac{S}{N} = 0 \tag{1}\label{1}$$ That is to say, I am considering those systems with a ...
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1answer
463 views

Prevost Theory of Exchange

I am having a trouble in understanding this concept. If bodies are at thermal equilibrium, there is no heat transfer. Heat is transferred through three different ways: Conduction, convection and ...
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1answer
62 views

Can a first-order autonomous system not at a fixed point, transition to a fixed point?

The following is from Introduction to Dynamics, by Percival and Richards: At each zero $x_{k}$ of the velocity field $v\left[x\right],$ $$v\left[x_{k}\right]=0,$$ so that a system ...
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1answer
687 views

Why frictionless joints are assumed in pin-joint truss analysis?

In pin-jointed truss analysis, we consider some assumptions. One of them is that they have friction-less joints. Why do we have this assumption? What would happen if the joints were to have ...
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4answers
546 views

How can we use potential energy curve to find stable/unstable equilibrium points?

In this question, how can we comment on the position of stable/unstable equilibrium if we don't know the total energy of the system? We know force is zero at points 'a', 'b', 'c' and 'd' but there ...
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2answers
285 views

Condition for neutral equilibrium

Do rate of change of force with respect to $x$ $\frac{dF}{dx} = 0$ at the equilibrium position imply that it is the neutral equilibrium position?
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1answer
245 views

Necessary vs sufficient condition for thermodynamic equilibrium in statistical mechanics

This question came to me after a discussion on another post on the site, which you can find here. I will restrict the following discussion to Hamiltonian systems. Also, I will use the abbreviated ...
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1answer
382 views

Why is reversible process quasi-static? [duplicate]

I really don't understand why this needs to be. To be reversible, isn't all we need is that there is no net energy change in the system so, who cares how fast or slow it goes?
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Understanding the Boltzmann factor

By a simple dynamical model one can derive the equilibrium distribution of $N = n_1 + n_2$ identical two-level particles which are subject to Boltzmann-like thermal fluctuations. Consider a particle ...
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1answer
110 views

Simple Harmonic Oscillation of a vertical Spring

If a spring with a spring constant of k is hung vertically, and a mass is attached to it the spring will rest in equilibrium at some distance h from the springs original equilibrium length because ...
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2answers
397 views

Static Equilibrium: Normal Force

Consider the following situation where an object (for example a person) is at rest at point D such that the system is in static equilibrium: Why is there no normal force present at point D? To my ...
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1answer
104 views

Why do bodies tend to attain thermal equilibrium

I am aware of the Zeroth Law of Thermodynamics, which defines thermal equilibrium and enables us, in effect, to measure the temperature of bodies using thermometers. However, my question is, why do ...
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1answer
53 views

What exactly is equilibrium?

What exactly is equilibrium? I'm riding my scooter and I get this doubt. The maximum power the engine of my scooter can deliver is constant. As I pull full throttle, the scooter accelerates, the ...
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3answers
312 views

Equilibrium of a rigid body

Why is it necessary for a body to have the net torque acting on it be balanced along with the forces for it to be in equilibrium? Isn't torque just some special case of force like rotation is a ...
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1answer
53 views

relation between quench and entropy

After a quench in a system, it gets turbulent and maybe goes too far from equilibrium situation, so after that, how the entropy and quench relating to each other? _ also what will happen to the ...
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3answers
73 views

In thermodynamics what does it mean that a system is taken through a series of small steps?

I'm struggling to understand this concept of reversible process as a transformation from a initial state i ( generic ) to a final state f, but done through small changes/steps. What does it mean that ...
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1answer
130 views

How should the hydrostatic equation be set up for the sun? [closed]

Beforehand I Solved the hydrostatic equilibrium for the sun with constant density. I am then asked with finding the density as a function of the radius, and evaluate what it will do to the ...
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1answer
507 views

oil and water- The Archimides' law

I have a problem as on the topic, see the below. First I added $25\hbox{cm}^3$ water in to a beaker. Then I added $2N$ oil onto it. But the level of the water was still $25\hbox{cm}^3$. My problem ...
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1answer
311 views

Brownian motion and equilibrium

I would like to know if when you consider a system in which you have Brownian motion if it is considered a system in equilibrium or far from equilibrium and why. i.e., is Brownian motion considered as ...
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1answer
61 views

Collisions in System in Equilibrium

Are all collisions between gaseous molecules and boundary in a system at Equilibrium, elastic? Why?
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1answer
134 views

If ice water equilibrium exists at 0C at 1atm then why don't oceans stay near freezing all time

The arctic ice is basically a giant floating sheet of ice laid upon the ocean so the ocean and ice are (probably) at equilibrium in the arctic. And since all oceans are connected shouldn't all of them ...