Questions tagged [equilibrium]

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Forces acting on an orange placed on a table in equilibrium [closed]

An orange sits on a table in equilibrium. What forces are acting on it? What is the reaction force to each of the forces acting on it? What are the action and reaction pair?
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1answer
154 views

How “Eyeball Glide Ball” toy works?

How this toy works? As you roll the ball on the table, the eye always point up: (original video source: https://youtu.be/_3kAjWaxM30) As far I am aware, no magnets are involved in the construction ...
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3answers
165 views

Why is boiling a non-equilibrium process? [closed]

Boiling is a non-equilibrium process. Which equilibrium (mechanical, chemical and thermal) are not maintained during boiling and why?
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4answers
645 views

Can a positively charged conductor have negative surface charge density somewhere?

This is a simple question that occurred to me while thinking about electrostatics. Let's consider a positively charged isolated conductor in equilibrium. In general, the surface charge density varies ...
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2answers
349 views

Why is the restoring force not zero at the equilibrium position of simple harmonic motion?

The restoring force is applied in order to take the body it's equilibrium. Then in a SHM why in the mean position restoring force maximum rather than being zero as it has reached equilibrium. (After ...
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2answers
558 views

Beam attached to a wall

Suppose I have a rigid beam attached to a wall, how can the reaction force on the point the beam is attached to generate a static equilibrium on the beam? ...
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0answers
483 views

Can a substance have zero vapour pressure above absolute zero?

According to this Reddit thread, the answer is no, vapor pressure can't be zero when temperature is above absolute zero. I suspect the answer might actually be yes according to a precise definition I ...
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1answer
57 views

Lagrange points and gravity

I have just found an article talking about the L1 to L5 equilibrium positions of gravitation around stars, planets, etc. As far as I could learn from this website and other research I have done the ...
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0answers
46 views

Is there an open quantum system analogue of the equilibration time bounds for classical ergodic Markov chains?

Background For classical ergodic discrete Markov chains, we can bound the time taken to reach the stationary distribution to the spectral properties of the transition matrix. I will outline this ...
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1answer
115 views

Why does the gas in Sun's outer layer not expand?

Since in the outer part of sun it consists gases. Why don't the gases expand due to heat? This was asked by my friend. And he said that the gases are attracted by the plasma layer by a force. So the ...
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1answer
137 views

What happend to the tension? [closed]

If crane with uniform arm raised by shortening cable,what is the effect to the tension of the cable?I know the tension will increase but what cause? Bcs of increasing in angle?Or got thing with torque?...
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2answers
987 views

Can a body be in equilibrium when only one force acts on the body? [duplicate]

I think that when we throw a body in air, at top point the body is in equilibrium but gravitational force is still acting. Is this correct?
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57 views

Defining a 'small disturbance which dampens in time' while identifying stable points in a nonlinear system

I'm reading the book "Nonlinear dynamics and Chaos" by S Strogatz. In section 2.2, titled "Fixed points and stability", he defines equilibrium points as solutions where ...all sufficiently small ...
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0answers
27 views

In terms of the greenhouse effect, what is the Earth's heat capacity?

Has the earth’s atmosphere reached an equilibrium at which the input radiation energy roughly equals its output, or is the output significantly lower than the input because the energy is being used to ...
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2answers
107 views

Electric charge and net force [closed]

Consider two point charges $+Q$ and $-Q$, which are fixed a distance $d$ apart. Can you find a location where a third positive charge $Q$ could be placed so that the net electric force on this third ...
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1answer
52 views

free stress boundary condition

I would like to understand better the free stress boundary condition. Indeed, force equilibrium writes $\nabla.\sigma=0$, and not $\sigma=0$, so which basic physical principle (such as force ...
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1answer
72 views

Demonstration that electric current at equilibrium is zero in crystals

As it is well known, electrons at equilibrium (no external field) do not conduct electric current, i.e. $\int_{BZ} dk\,v_{k}\,f(\epsilon_k)=0$ where $f(\epsilon_k)$ is the Fermi-Dirac distribution $...
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2answers
307 views

Thermal equilibrium vs steady state

According to Kirchhoff's law, when two objects are in thermal equilibrium, both objects have the same temperature and each object emits as much energy as it absorbs. Also, the energy absorbed at each ...
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1answer
112 views

Why physically do things in general tend to move toward a lower potential value in a potential field? [duplicate]

There are many answers on the site discussing motion of electrons in an electric potential field, See Why is voltage described as potential energy per charge? but also mass tends to move toward a ...
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1answer
48 views

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
62 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
343 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
83 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
415 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
702 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
99 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
72 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
89 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
148 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
89 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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2answers
227 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
215 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
170 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
557 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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42 views

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
94 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
280 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
256 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
132 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
84 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
190 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
327 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
285 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
89 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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3answers
60 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
1k 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-balances itself. But how ...
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2answers
144 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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162 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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535 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 ...