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16 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 ...
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8answers
13k views

Why does maximal entropy imply equilibrium?

From a purely thermodynamical point of view, why does that entropy have to be a maximum at equilibrium? Say there is equilibrium, i.e. no net heat flow, why can the entropy not be sitting at a ...
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1answer
41 views

Find the indicated quantities from the given data [on hold]

This is a vector application. A rope is hung at both ends from a horizontal beam, and a weight m is suspended from it as shown in the figure. The left part of the rope exerts a force G at P, while ...
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0answers
23 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
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1answer
29 views

Do all equillibrium points of a discrete mapping show up on the bifurcation diagram?

The question in the title is perhaps vaguely posed, so I'll include the concrete example which is bugging me. Suppose we have a mapping given by $$N_{t+1}=N_t\cdot ...
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2answers
1k views

Why do most office chairs have 5 wheels?

(Inspired by Why are four legged chairs so common?) I've been wondering for a while... Why do most wheeled office chairs have 5 wheels? My guess would be that while stability vs. simplicity ...
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2answers
21 views

What determines whether a mobile will hang in stable or unstable equilibrium?

Asking for a friend trying to make a Calder-style hanging mobile: https://www.google.com/search?q=mobile+calder&tbm=isch I understand torque just well enough to get it to balance (theoretically). ...
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1answer
362 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 ...
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1answer
27 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 ...
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1answer
35 views

Two strings in static equilibrium. Why not use the pythagorean theorem to combine vectors? [closed]

I have been working through a physics course and came across the problem: two strings holding a weight in static equilibrium. It all made sense, except for this: Why don't you use pythagorean theorem ...
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1answer
255 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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2answers
40 views

Why don't barbells tip over when a 45 is placed on one side?

A standard barbell is 45 pounds, as is the heaviest weight available in most gyms. When a weight is placed on the side of a barbell, some of the barbell is to the "outside" of the weight, like so, so ...
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1answer
50 views

If two gasses are in thermal equilbrium, do their molecules have same amount of Kinetic energy?

If two gasses are in thermal equilbrium, do their molecules have same amount of Kinetic energy?
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1answer
3k 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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3answers
1k views

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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0answers
35 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 ...
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0answers
35 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 ...
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0answers
20 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 ...
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1answer
44 views

Orbital but stationary motion

Is there a place between the Moon and Earth where an object can rest freely and revolve with the Moon? What is that called?
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2answers
40 views

Equilibrium on a fixed wedge

While solving a question I came acrross this doubt.For a block in equilibrium on an inclined wedge, the summation of forces should be equal to zero.I am confused because I got two different results ...
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1answer
43 views

Why there is an extra componet of force in this Equilibrium state?

I have a question about the forces on a body at equilibrium. Look to this image: here i draw a man standing with a pen on earth. And I think that I draw all possible forces on it. They are as ...
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2answers
58 views

Equilibrium equations

You have one horizontal beam. Its left point is attached to a free pivot at the vertical wall. Its right point is suspended by a rope from the ceiling. Nothing is moved. So $\sum F=0$ and $\sum M=0$. ...
0
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0answers
52 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}} = ...
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0answers
17 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, ...
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1answer
86 views

Discrete time simulation of gas liquid equilibrium in a tank

I am trying to write a discrete time simulation of liquid/gaseous oxygen in a pressurised cryogenic fuel tank. For now I am assuming that the only external change to the system is the influx of heat ...
0
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0answers
38 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 ...
2
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1answer
68 views

Volume as a choice of measure in phase space

For equilibrium systems, we expect the Liouville theorem to hold. This theorem states that the density function of the states of the system is a constant of motion, which in turn can be translated ...
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2answers
762 views

Metal sphere and charged ring

I think this is an interesting question, to which I don't really know the answer to. (Also, not a homework question.) Say you have an uncharged metal sphere constrained to move in the z-axis. There ...
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1answer
43 views

Conceptual Ice Water Equilibrium

We observe that when we apply pressure on on Ice Water equilibrium system then more of ice melts.. Ice(more Volume) + Heat ----><----- Water (Less volume) If we increase pressure then volume ...
0
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2answers
54 views

Why does the mass on the cart-pole have to fall?

Not sure if I am posting this question in the correct community, as it relates primarily to reinforcement learning. Apologies early on if this is not so. In reinforcement learning many algorithms ...
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1answer
997 views

Spikes on ferrofluid?

What exactly are the spikes, or peaks and valleys, caused by in pictures such as these Wikipedia states that "From the point of view of magnetic energy, peaks and valleys are energetically ...
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2answers
3k 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 ...
0
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1answer
23 views

Can there be net condensation into a pool of water?

I'm curious about the equilibrium of evaporation and condensation. Given that the surface area of a dehumidifier's evaporation coil at 4C is proportional to the rate of condensation, how would the ...
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0answers
24 views

Roberval Balance [closed]

Is there any mathematical/mechanical article that explains in detail why the Roberval balance is taken place? I generally observed that the classical mechanisms are not analysed in detail, even in ...
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4answers
251 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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0answers
90 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
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1answer
160 views

Local and global detailed balance

I'm taking a course on nonequilibrium statistical mechanics and I encountered the terms local and global detailed balance. I'm a bit confused about what is their exact definition and what is the ...
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0answers
61 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?
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1answer
140 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
64 views

Balancing a bowl of water

Let's say you have a mildly elliptical bowl balanced on top of a stick. This bowl is filled with water, not necessarily to the top but fairly full (I'm not 100% sure this makes a difference). You then ...
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1answer
217 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 $$ ...
0
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1answer
116 views

How far does the man have to walk down the beam in order to tip the beam off fulcrum A? [closed]

I have set the sum of the forces in the y equal to zero and calculating the torque around B, I get that he walks 7.9. I don't have an answer key, but I don't believe this is the correct answer. I ...
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6answers
2k views

If the Earth is in constant motion then why do we say that an object is in a state of rest?

I got this question as my physics class homework for tomorrow. Anyone please help me out. If Earth constantly rotates and revolves, then how can we call an object in a state of rest?
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1answer
113 views

Why is it effectively impossible to balance this rectangle block on a triangle block? (See photo)

I've always wondered why it's basically impossible to balance a rectangle block on top of a triangle one like this. This is my nine-year-old giving it a try. I have never in my life gotten it to ...
0
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2answers
48 views

Pertaining to Newton's laws, how do so many objects acheive perfect equilibrium?

Suppose a light is hanging from a ceiling. Supposedly, the force of tension pulling it up is exactly the same as the force of gravity pulling it down. Why is it that the tension happens to be exactly ...
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3answers
308 views

Is it true that spring has more force acting on it at its positive maximum amplitude than than at the negative one?

Am I missing something? It seems obvious to me that at $+A$ and $-A$, the spring has restorative forces equal in magnitude but opposite in direction. But since gravity is always pulling it down, ...
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1answer
117 views

How exactly do walking canes and crutches help?

I am reading introductory physics, and there is a chapter on equilibrium. In the chapter, the author mentions how devices can exploit distribution of forces to help those that are physically ill, via ...
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1answer
45 views

How does phonon scattering change the distribution function?

For a one-dimensional structure, we know that the modified distribution function has the following energy dependency in equilibrium: \begin{equation} Z(\varepsilon)\,f(\varepsilon) = ...
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4answers
2k views

Prove that negative absolute temperatures are actually hotter than positive absolute temperatures

Could someone provide me with a mathematical proof of why, a system with an absolute negative Kelvin temperature (such that of a spin system) is hotter than any system with a positive temperature (in ...