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1answer
96 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 ...
2
votes
1answer
161 views

Earnshaw's theorem and springs

Earnshaw's theorem states that the Laplacian of the potential energy of a small charge moving through a landscape full of static negative and/or positive charges (and gravity) is zero. Thus you can't ...
0
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0answers
98 views

Can I make a cold air trap (thermal equilibrium)

Thermodynamic buoyancy. I have an air intake for combustion air entering into a basement furnace room. During cold weather, the air enters unchecked (no damper on pipe is allowed). I have this 5 ...
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0answers
54 views

Equilibrium Condition

In classical thermodynamics, equilibrium conditions means maximum entropy for a closed state. However, people always talk about equilibrium for open systems as well. How can one say that an open ...
1
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1answer
415 views

Classify equilibrium points and find bifurcation points of a non-linear dynamic system

Context: The question refers to computational physics of non linear systems with Mathematica. Excercise: Given the system $\{f_1: \dot{x} = a x + y + x^3, f_2: \dot{y} = x - y \}$: Find the ...
1
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1answer
148 views

Can exergy and exergy destruction be understood through thermodynamical and/or statistical-mechanical principles?

My textbook Fundamentals of engineering thermodynamics, Moran and Shapiro states: The exergy is the maximum theoretical work obtainable for an overall system consisting of a system and the ...
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2answers
284 views

Equilibrium - uniform circular motion

Maybe this is a bit of a silly question, but let us pretend we have a pendulum in a ideal universe with no friction, drag, or anomalous forces there to affect it. Additionally, our pendulum is ...
4
votes
6answers
455 views

Why a system should be at its lowest energy state for its stability?

Every possible reaction in chemistry is to attain stability. In physics, the alignment of an electric dipole in an external electric field and in all other physical systems (at least those I study in ...
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3answers
300 views

Airplane with banner in a windy day

Will the banner of this airplane be always in the proper direction if the airplane flies in any direction on a windy day?
1
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1answer
69 views

Uniqueness of equilibria in electrostatics

I have the following problem. Suppose we place some continuous charge distribution (with total charge $Q$)on some conducting domain. The charge will redistribute itself on the domain until it's in ...
0
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2answers
615 views

Forces acting on a body in equilibrium

The resultant force acting on a body in equilibrium is 0: $$\iiint_R \rho {\bf b}\ dV + \iint_S {\bf t}^{(n)} ds = 0,$$ in which $R$ is a region inside the body, $\rho {\bf b}$ the body force per ...
2
votes
1answer
2k views

Estimate temperature and pressure of steam in a pot of boiling water

Suppose we have a pot of known dimensions filled to level L with boiling water on a stove, covered by a lid with a vent of known dimensions. Given the steady-state temperature of the stove (bottom of ...
1
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0answers
53 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 ...
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0answers
1k 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 ...
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0answers
1k views

Given a potential energy function, find the natural frequency of small oscillations about stable equilibrium [closed]

This was a problem given to me on a quiz and I am having trouble with mainly part b, I know how to do part c once I get my solution to b. A particle of mass $m$ is constrained to move along the ...
0
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3answers
2k views

Lowest point of a loose cable with a pulley/mass hanging from it [closed]

This is part of a homework question which I've been stuck on for several hours. I've tried googling "lowest point of rope", "lowest point of hanging cable", "lowest point of pulley", and a bunch of ...
3
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3answers
5k views

When a ball is tossed straight up, does it experience momentary equilibrium at top of its path?

This question has been asked many times all over the Internet and answers can be found on places such as yahoo and ask.com, but I'm not satisfied with those answers and I don't trust the validity of ...
1
vote
1answer
1k views

Tension on pulleys Physics Question [closed]

Collar A is connected to a 50lb load on a frictionless horizontal rod. Determine magnitude of P to maintain equilibrium when x=4.5. Im confused on the concept of Tension I originally got the ...
0
votes
2answers
514 views

Equilibrium of Force Systems including Torque

please help me to solve this problem.. this is only the #3 on my homework and the only thing i didn't know here is how to calculate the tension T. please teach me how to solve the tension here ...
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0answers
1k 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 ...
1
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1answer
2k views

Kirchhoff law of thermal radiation

Kirchhoff's law of thermal radiation states that for thermal equilibrium for a particular surface the monochromatic emissivity $\epsilon_{\lambda}$ equals the monochromatic absorptivity ...
0
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1answer
260 views

Equilibrum position of an extensible spring

A stone of mass $m$ is attached at one end of a vertical spring whose another (upper) end is fixed at horizontal surface. During the motion, a spring takes vertical direction. Force in spring is ...
1
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0answers
78 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 ...
0
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1answer
390 views

Calculating the amount of dissolved gases in a liquid?

The most basic situation, water at room temperature, has dissolved oxygen, CO2, and more. Why is this? How would one calculate how much gas should be dissolved in any given liquid?
4
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2answers
289 views

The “stationary potential energy” condition for static equilibrium in mechanical systems

I've often read that, for a mechanical system which can be described by $n$ generalized coordinates $q_1,...,q_n$, a point $\mathbf{Q}=(Q_1,...,Q_n)$ is a point of equilibrium if and only if the ...
5
votes
1answer
179 views

Fluids in thermodynamic equlibrium

I am reading about the Euler equations of fluid dynamics from Leveque's Numerical Methods for Conservation Laws (Amazon link). After introducing the mass, momentum and energy equations, some ...
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4answers
302 views

Dissolving oxygen into water

I was wondering how one would actually calculate how much oxygen would dissolve into water given the necessary initial conditions, and what those initial conditions would need to be. I assume they ...
0
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2answers
667 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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2answers
2k 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?
5
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3answers
334 views

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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vote
2answers
628 views

Force analysis on truss [closed]

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. ...
3
votes
2answers
414 views

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 ...
0
votes
1answer
387 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 ...
10
votes
1answer
525 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 ...
3
votes
1answer
487 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 ...
1
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0answers
45 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 ...
15
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4answers
3k 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. ...
1
vote
0answers
314 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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votes
1answer
450 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 ...
1
vote
2answers
471 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 ...
0
votes
1answer
485 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 ...
4
votes
1answer
787 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 ...
0
votes
1answer
354 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 ...
0
votes
1answer
128 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
votes
2answers
418 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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votes
1answer
1k views

Lennard-Jones potential - equilibrium [closed]

If I have Lennard-Jones potential, how can I calculate equilibrium? $$ U(r)=\epsilon \left ( \left (\frac{r_m}{r} \right )^{12}-2 \left (\frac{r_m}{r}\right )^6 \right ) \ $$
3
votes
3answers
241 views

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, ...
4
votes
1answer
223 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 ...
0
votes
1answer
633 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 ...
20
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3answers
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 ...