The equilibrium tag has no wiki summary.
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Chemical Equilibrium - Why does changing the temperature shift the equilibrium? [migrated]
I know that raising the temperature in a reversible chemical reaction causes the equilibrium to shift to the endothermic side.
I know that $\Delta G = \Delta H - T \Delta S$ but I don't know how to ...
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1answer
38 views
Equilibrium and Torque [closed]
How does one calculate the forces that exert on a wooden board held by two trestles if one knows the weight of the board as well as the distance of both trestles?
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2answers
63 views
Minimization of energy and maximization of entropy
Are maximization of entropy and minimization of energy equivalent? Or are they contrary?
Why should the thermodynamic potentials such as $G$, $A$, etc, be minimum at equilibrium?
I am confused. ...
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3answers
83 views
How would you determine whether an object is at equilibrium? [closed]
How would you determine whether an object is at equilibrium or not?
What is the definition of equilibrium?
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1answer
91 views
Problem about moments and equilibrium. [closed]
A plank is on top of 2 branches. It is in contact at 2 points, A and B. The plank is 90 cm long. A is on the left of B. A is 15 cm from the left end of the plank. B is 20 cm from the right end of the ...
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3answers
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Will Cone standing on its tip, without any other force other than gravity topple?
A cone standing on its tip is considered to be in unstable equilibrium as a slightest force could topple it. So, if the cone is stood on its tip with no other force other than gravity (and the ...
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1answer
95 views
Force analysis on truss
I am reading a book on fundamental physics for mechanics. There is a truss shown in the figure. A train of mass $M=56$ ton is resting at the middle point of AC, ignore all the mass of truss and rails. ...
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2answers
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Pumping water from a closed column. Will the column get empty or just circualte?
As a picture is worth a thousand words, here is my problem:
It is a closed water column with a bit of air in the top section.
If I run the pump and make the water flow from IN to OUT,
Will the ...
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1answer
123 views
Chemical Equilibrium - Why do changes in pressure cause a shift in the ratio of products and reactants?
I understand Le Chatelier's principle and how every change to an equilibrium system causes an opposing reaction from the system. I also understand how, when pressure is increased, the equilibrium ...
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1answer
176 views
Why is (von Neumann) entropy maximized for an ensemble in thermal equilibrium?
Consider a quantum system in thermal equilibrium with a heat bath. In determining the density operator of the system, the usual procedure is to maximize the von Neumann entropy subject to the ...
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0answers
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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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0answers
38 views
Any new texts directly on second law of thermodynamics? [duplicate]
Possible Duplicate:
Recommendations for Statistical Mechanics book
Is anyone aware of any recent text that summarises the research and arguments on second law of thermodynamics and also on ...
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0answers
314 views
How to find Rotational and Translational Equilibrium of Hanging Masses on a Bar?
I am making a hanging mobile which needs to be done mathematically by calculating torque. The problem is, I can't seem to figure out how to solve for the distance of the two masses from the pivot ...
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5answers
765 views
Why does the nature always prefer low energy and maximum entropy?
Why does the nature always prefer low energy and maximum entropy?
I've just learned electrostatics and I still have no idea why like charges repel each other.
...
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0answers
85 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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1answer
188 views
How to properly find equilibrium vectors when 3 or 4 vectors are present? [closed]
I'm having trouble regarding how to find the equilibrium of vectors. We were given tables with given information and had to fill them in; I'm fairly sure my initial attempts were incorrect.
first ...
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2answers
265 views
To find whether a particle is in equilibrium or not
Actually the following question came in an exam i gave yesterday. I know the site does not allow home-work type questions, but as I am having a conceptual problem in solving the question, I am posting ...
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1answer
281 views
Torque and equilibrium
I am a little stuck on the concept involved in part b) of the following problem:
A $5 m$ long road gate has a mass of $m = 15 kg$. The mass is evenly distributed in the gate. The gate is supported at ...
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1answer
389 views
Understanding moments as forces?
I was watching this lecture on analysis of stress for mechanics of materials. At time 7:20, the lecturer says that in equilibrium, the sum of forces and "moments" in each direction (x,y,z) must be ...
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1answer
141 views
Calculate the stable height of a balloon
My son has asked me a question, and I'm afraid my high school maths are not up to the task:
Is it possible to calculate the height that a given balloon (filled with a known quantity of helium) will ...
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1answer
71 views
Evolution of Gibbs energy change of reaction with temperature
The Gibbs energy change of reaction is given by $$\Delta G^0_{rx}=\Delta H^0_{rx}-T\Delta S^0_{rx}$$
From the look of it seems the direction of variation of equlibrium with $T$ is given by the sign ...
3
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2answers
269 views
Time to establish saturated vapour pressure above liquid
Thought experiment - a liquid is in a closed container in equilibrium with its vapour, and then suddenly all the vapour is pumped away. Switch off the pump so that instantaneosuly there is no vapour ...
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1answer
401 views
Lennard-Jones potential - equilibrium [closed]
If I have Lennard-Jones potential, how can I calculate equilibrium?
$$ U(r)=\epsilon \left ( \left (\frac{r_m}{r} \right )^{12}-2 \left (\frac{r_m}{r}\right )^6 \right ) \ $$
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3answers
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What are some creative illustrations of the nature of dissipative forces?
I'm teaching a conceptual introduction to physics for American 13-15 year old students this summer.
One of the main ideas I want to hit on is the relationship between energy conservation, ...
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1answer
153 views
Is this formula for the energy of a configuration of 3 fluids physically reasonable?
I have studied for a couple of months now a mathematical model of the energy of a configuration of immiscible fluids situated in a fixed container such that the fluids fill the container. In other ...
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1answer
366 views
Can anyone solve this simple static equilibrium problem? [closed]
A bridge is 50m long, has a mass of 20,000kg, and rests on two pivots, A and B. The distance between A and the left side of the bridge is 10m. The distance between B and the right side of the bridge ...
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3answers
881 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 ...
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2answers
183 views
When do thermal and chemical equilibrium not coincide?
What is an example for a system, which is in chemical equilibrium, but not in thermodynamical equilibrium?
And what about the other way around?
It seems to me, that as long as Parameters like ...
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1answer
337 views
Examples of immiscible or wall-climbing liquids
I am very interested in the physics of immiscible fluids. I would like to ask you if you know any source or list of experiments done by others, with two or three liquids. I am interested in the final ...
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4answers
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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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4answers
193 views
Is “equilibrium state” equivalent to “well-defined state variables”?
Follow up to
Intuitively, why is a reversible process one in which the system is always at equilibrium?
and
How slow is a reversible adiabatic expansion of an ideal gas?
Suppose you have a ...
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2answers
175 views
why egg cooks slowly in mountains?
A quick Google tells me "Because water boils at a lower temperature at high altitudes". But I am not being able to understand this answer and fill-in the gap. Like, how does an egg cook in the first ...
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How do we perceive hotness or coldness of an object?
Some objects, especially metallic ones, feel cold on touching and others like wood, etc. feel warm on touching. Both are exposed to same environment and are in their stable state, so some kind of ...
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Applying the Maxwell–Boltzmann statistics to astrophysical objects
Quoting Wikipedia:
In statistical mechanics, Maxwell–Boltzmann statistics describes the statistical distribution of material particles over various energy states in thermal equilibrium, when the ...
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1answer
338 views
Statistical physics of molecular dissociation of a diatomic gas
Say there are $N$ atoms of type $A$ in a box of volume $V$ and they are undergoing a reversible association-dissociation reaction $A + A = A_2$.
Let an $A$ atom have mass $m$, and hence the molecule ...
1
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1answer
284 views
Upper equilibrium point of a pendulum with small perturbations
I remember the following fact about a rigid pendulum:
The point when the pendulum weight is lowest is a stable equilibrium while the point where the pendulum weight is highest is an unstable one.
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7answers
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Why is the Earth so fat?
I made a naive calculation of the height of Earth's equatorial bulge and found that it should be about 10km. The true height is about 20km. My question is: why is there this discrepancy?
The ...
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2answers
666 views
Calculate stainless steel pole necking limit
Background
Trying to determine how much weight a post can support without necking when a monitor is attached to an articulated arm: a cantilever problem.
Problem
There are three objects involved in ...
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1answer
144 views
Boltzman distribution for chemical potentials
I read that if we have a system with two co-existing phases with chemical potentials respectively $\mu_1$ and $\mu_2$ then, at the equilibrium, the concentrations $X_1$ and $X_2$ are related by the ...
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What determines the (minimum) angle at which a domino falls over?
Dominoes, when placed upright, remain that way. Sometimes, even if you tip them a little bit, they will go back to their upright position.
However, if you tip them too far, they will fall over.
...
