What is Equilibrium: Definition and 1000 Discussions

Thermodynamic equilibrium is an axiomatic concept of thermodynamics. It is an internal state of a single thermodynamic system, or a relation between several thermodynamic systems connected by more or less permeable or impermeable walls. In thermodynamic equilibrium there are no net macroscopic flows of matter or of energy, either within a system or between systems.
In a system that is in its own state of internal thermodynamic equilibrium, no macroscopic change occurs.
Systems in mutual thermodynamic equilibrium are simultaneously in mutual thermal, mechanical, chemical, and radiative equilibria. Systems can be in one kind of mutual equilibrium, though not in others. In thermodynamic equilibrium, all kinds of equilibrium hold at once and indefinitely, until disturbed by a thermodynamic operation. In a macroscopic equilibrium, perfectly or almost perfectly balanced microscopic exchanges occur; this is the physical explanation of the notion of macroscopic equilibrium.
A thermodynamic system in a state of internal thermodynamic equilibrium has a spatially uniform temperature. Its intensive properties, other than temperature, may be driven to spatial inhomogeneity by an unchanging long-range force field imposed on it by its surroundings.
In systems that are at a state of non-equilibrium there are, by contrast, net flows of matter or energy. If such changes can be triggered to occur in a system in which they are not already occurring, the system is said to be in a meta-stable equilibrium.
Though not a widely named "law," it is an axiom of thermodynamics that there exist states of thermodynamic equilibrium. The second law of thermodynamics states that when a body of material starts from an equilibrium state, in which, portions of it are held at different states by more or less permeable or impermeable partitions, and a thermodynamic operation removes or makes the partitions more permeable and it is isolated, then it spontaneously reaches its own, new state of internal thermodynamic equilibrium, and this is accompanied by an increase in the sum of the entropies of the portions.

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  1. R

    Static equilibrium against a wall

    Homework Statement A uniform strut of length, L and weight 780 N is free to pivot about point P where it is attached to the wall (see diagram) A weight W = 815 N hangs straight down from the end of the strut. A rope is attached to the same end as the load and the wall completes the support as...
  2. M

    Plate conductor in electrostatic equilibrium

    Homework Statement A thin, square, conducting plate 50.0 cm on a side lies in the xy plane. A total charge of 4.00 x 10-8 C is placed on the plate. Find (a) the charge density on each face of the plate, (b) the electric field just above the plate, and (c) the electric field just below the...
  3. R

    (GRADE 9 SCIENCE) Equilibrium Tension Force Help Me PLease

    Hey Guys, Well I am a freshman taking Physical Science and my teacher didn't do a good job explaining this question. http://prntscr.com/uf6tv <-- that's the problem and i numbered the 6 questions If you could answer those questions and explain how you got that it would be awesome! thanks
  4. C

    Calculating Total Internal Energy of a System in Thermal Equilibrium

    Homework Statement Consider a system in thermal equilibrium consisting of N particles that have 2 energy states E1 and E2 separated by an energy ΔE. Given that $$N_1 = \frac{N}{exp(-ΔE/k_BT)},\,\,N_2 = \frac{N exp(-ΔE/k_BT)}{1+exp(-ΔE/k_BT)}$$ show that in the case of the lowest energy...
  5. J

    Equilibrium under the action of concurrent forces

    Homework Statement Hello all, I just finished a question on equilibrium. I wish I could upload a diagram or something but I don't know how to get it from my Microsoft oneNote to here. But basically there is a mass held In equilibrium by two ropes. on the left is mass 2 and on the right is mass...
  6. N

    Equilibrium solutions of a spherical pendulum

    Homework Statement A spherical pendulum consists of bob of mass m attached to a massless rod of fixed length R. The end of the rod opposite the bob pivots freely (in two directions) about some fixed point. For the conical pendulum (θ=constant) case, show that the conical angle is stable...
  7. J

    For Statics:Simple Systems of Equations to Solve Equilibrium Problems

    Homework Statement I have a picture attached with this static equilibrium problem. (Solve system for Fac and Fab) Homework Equations Sum of x and y both=0The Attempt at a Solution I just don't have a systematic easy approach to solving these systems. Does anyone have one? From the picture...
  8. S

    Equilibrium Distribution of Electrons and Holes

    Hello. I was studying the Semiconductor and I am confused with this diagram. I have attached the diagram. Please tell me briefly what does this diagram say. So that I could ask further. I have confusion with this diagram. I don't want to be specific so that you describe the whole diagram...
  9. J

    Equilibrium temperature distribution in gravitational field

    I came across Tolman's paper on the equilibrium distribution of temperature in gravitational field. He argues that in contrast to classical thermodynamics situations, in gravitational field, a fluid in thermodynamic equilibrium will not have the same temperature everywhere (as measured by...
  10. Q

    Need help on a forces and equilibrium question

    Its part B that I'm not sure about. I know how to do it. But I'm confused about why the support force is not acting vertically upwards (so no horizontal component). I assumed that the support force would always be directly perpendicular to the ground/slope/wall. Can someone explain this?
  11. C

    Rotational Equilibrium and Normal Forces

    Hi, The question I have is not for a numerical answer but for clarification. Some of the questions involving torque/rotational equilibrium describe a person standing on a plank. I know that the gravitational force of the person on the plank needs to be considered for translational and...
  12. E

    Does this ODE have an equilibrium?

    Homework Statement Two reservoirs are connected. Water drains from one reservoir to the other, governed by the following ODE: dh/dt= -k1*(h)^0.5 -k2*(h-H)^0.5 , H<0, k1,k2>0 Does an equilibrium exist? What happens in terms of Picard's Existence Theorem? Draw a phase diagram of possible h*...
  13. S

    3D tension problem (static equilibrium)

    Homework Statement A block of weight 50N is hung by 3 cables from the ceiling. Each rope ZA, ZB, ZC converges at Z so that they form a tetrahedron. (ZA=ZB=ZC=AB=BC=CA). Find the magnitude of the tension of each cable. a=0 tetrahedron symmetryHomework Equations F=mgThe Attempt at a Solution I...
  14. S

    Equilibrium question on review assignment, quick (I have a test tomorrow).

    Homework Statement A rod of negligible mass is supported by a hinge at the wall by a horizontal wire fastened at a 30 degree angle one-third of the way along the rod. A weight of 12 N hangs from the left end of the rod. a) Find the tension (T) in the horizontal wire. (T = 62.2 N) b) Find...
  15. S

    F = MA 2010 # 11 (Static equilibrium, 3 masses on a string)

    Homework Statement See: http://www.aapt.org/physicsteam/2010/upload/2010_FmaSolutions.pdf Question 11Homework Equations T_net = 0 F_net = 0 The Attempt at a Solution Start with F_net = 0: Let T1 be the force of tension on the left, T2 on the right T1cosθ=T2cosθ Y components: T1sinθ+T2sinθ = mg...
  16. N

    Finding and labeling equilibrium points between multiple point charges.

    Homework Statement How to find equilibrium points between four point charges? How do you determine whether these equilibrium points are stable, unstable, or neutral? I know the sum of the forces should equal zero, but that's it. How do you determine the stability of the equilibrium...
  17. S

    Objects in dynamic equilibrium

    What makes objects in dynamic equilibrium move? It can't be gravity because then it would only be one force and if an object is under the influence of one force, then it cannot be in equilibrium. Any help would be appreciated.
  18. A

    Solving Two Physics Questions: Rotational Inertia & Equilibrium Temp.

    Two masses, 300 g and 400 g, are connected by a cord that passes over a pulley with a radius of 6.64 cm (an Atwood's machine). When released from rest, the 400-g mass falls 60 cm and the 300-g mass rises 60 cm in 4.00 seconds. Find the rotational inertia of the pulley. Four 100-g ice cubes at...
  19. A

    Equilibrium and Statics involving a mass attached to three strings

    Homework Statement Find the forces of the three strings of this image. http://www.flickr.com/photos/79276401@N05/8395815988/in/photostream Homework Equations Using gravitational constant to find force of the mass. Using algebra to find the forces of the three strings. The Attempt at a...
  20. S

    Torques in equilibrium w/ angle

    on a meter stick the pivot point is placed at 1/4 its length; predict the force needed to balance the meter stick by pulling upward on the end of it with a string making an angle of 30 degrees w/ respect to the vertical. Me trying to solve it: sigma T=0 T1+T2=0 T1 = 0 <--this is the pivot...
  21. P

    Static Equilibrium with buoyant force. High difficulty.

    Homework Statement I attached the original problem and a diagram I made with the variables on it. Basically we have a rod hanging from a wire at an angle theta with tension and the other end floating in water. So there is T=tension, weight=w=mg and buoyant force=F_b. I introduced symbols for...
  22. H

    Equilibrium for diffusion of gases in metals

    Hi there, This could be absolute nonsense but I just got thinking about this. Say you had a certain metal into which a quantity of hydrogen had diffused, and then you placed it in communication with another hydrogen-free metal (say, titanium), would it be possible that the hydrogen would move...
  23. H

    Rotational and Translational Equilibrium Help Needed

    Homework Statement 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. You see, all of the problems we did in class talked about finding mass, but to do this project, I already...
  24. M

    Distance between point charges in equilibrium (simple)

    Homework Statement Two fixed charges, +1.07 uC and -3.28 uC, are 61.8 cm apart. Where may a third charge be located so that no net force acts on it? Homework Equations Coulombs law The Attempt at a Solution q1 = 1.07 uC q2 = -3.28 uC q3 = q q1 ----- q2 ----- q q1 and q2...
  25. D

    The equilibrium in the universe ?

    is it true that all matter and everything in this universe microscopic or macroscopic have a tendency to go to an equilibrium state ?
  26. L

    Equilibrium - The physics of a clothesline.

    Homework Statement A clothesline is attached to two fixed ends which are 10.0m apart. A pulley of mass 40.0kg hangs freely in the middle of the line. The sag at the centre is 0.20m. Find the tension in each half of the clothesline. Homework Equations The Attempt at a Solution...
  27. H

    Finding Equilibrium: How to Solve Force Problems Involving Poles and Objects?

    Homework Statement A pole is suspended horizontally between a wall and an attached string.(See the attachment). An object(W) is hanging from the pole at a distance of x from the wall. Find the value of x that preserves the equilibrium. 1) the angle between the pole and the...
  28. U

    Help understanding dynamic equilibrium

    Homework Statement if the equilibrium rule states ƩF=0N, how can something move or be moving at a constant speed ? eg I push on a box with 50N and friction provides 50N back, resulting in ƩF=0N. So I am not providing more N than the box is resisting with. I thought something could only be...
  29. P

    Been bothered by this equilibrium problem

    Homework Statement The sign for Lew's Bait Shop and Sushi Restaurant is a uniform rectangle, 1.50m wide and 0.800m tall, weighing 300N. It is supported by a wire at its upper-right corner and a pivot at its lower left corner. a) Late one night the wire was cut while the sign stays in...
  30. R

    Static Equilibrium for an object in 3-dimension

    I have studied a few online sources about static equilibrium in a mechanical system. My overall understanding is that for an object to be in static equilibrium, two following conditions have to be fulfilled: 1) Vector sum of all external forces that act on body must be zero. 2) Vector sum of...
  31. B

    Rigid Object In Static Equilibrium

    Hello, I am currently reading the about the topic mentioned in the title of this thread. In my textbook, the author gives the example with the wine-bottle and it's holder (I attached a photo). In this example, the author states that in order for this to be in static equilibrium, the second...
  32. R

    Horizontal Spring Pulled from Equilibrium?

    I don't necessarily understand the explanation given to the solution. Is it basically saying: A (valley) --> 0 (equilibrium) --> -A (valley) --> 0 (equilibrium) --> A (valley)?
  33. T

    Calculating Equilibrium Mass in a Pulley System

    Homework Statement Find the mass necessary for equilibrium to occur in the following image. Assume that the mass and the friction of the pulleys are negligible. Homework Equations None directly provided for this problem. The Attempt at a Solution I figured for this problem I...
  34. Telemachus

    Chemical equilibrium, getting molarity given pH and Kb

    What should be the molarity in an aquatic dissolution for Trimethylamine, ##(CH_3)_3N## if ##pH=11,2##? ##(CH_3)_3N+H_2O \rightleftharpoons (CH_3)_3NH^++OH^-##, ##K_b=6.3 \times 10^{-5}## I know that ##pH+pOH=14 \rightarrow pOH=2.8##, then ##[OH^-]=1.58 \times 10^{-3}## And...
  35. Y

    Equilibrium Partial Pressure Kp/Kc Question

    Homework Statement At 100 o C Kc=.078 for the reaction SO2Cl2<-->SO2 + Cl2. In an equilibrium mixture the [SO2CL2]=.0108 M and [SO2]=.052 M. What is the partial pressure of Cl2 in the eq. mixture? Homework Equations Kp=Kc(RT)\Deltan P=RT/V The Attempt at a Solution I solve for...
  36. K

    Chemical Equilibrium with Multiple Kc

    Homework Statement Compound A can react to form B and C according to the following A<->2B Kc=1 A<->C Kc=1 If 1 mole of A is solved into 1 litre of water, what will the concentration of A be after equilibrium has been reached?Homework Equations ICE-tables(?) A<->2B+C Kc=([B]^2[C])/[A] The...
  37. L

    Engineering Statics Equilibrium

    hi, for question two on the attached pdf, how would the equilibrium in the x work? From what i understand there must be an x and y component for the pin support at A because it acts at an angle but the support at B only has a y component because it is a rocker.
  38. T

    Finding Equilibrium Price and Quantity for Education at Harvard

    Homework Statement Assume Harvard has the following marginal cost equation and acts like a competitive firm: MC = 10X + 100 The aggregate demand for education at the College is: X^D("D" simply stands for demand)= 200 - .5p The demand function above does not account for an additional...
  39. H

    Equilibrium of a system consisting of two bodies

    Homework Statement The attachment shows a simple diagram of a system consisting of a Sphere(uniform) and and rod(uniform) in equilibrium. The rod is in rough contact with the sphere and hence there would be friction (acting vertically at the point of contact of the two objects). Both...
  40. S

    Static vs. Neutral Equilibrium of a Mesh

    Suppose a square metal mesh sheet is hung off-center from a string and you are charged with the task of hanging various weights so that the mesh will be in static equilibrium, roughly horizontal. Why is it that this task must be done with masses that can exert torques large enough to flex the...
  41. S

    Equation for translational equilibrium for horizontal components of force

    searching for equation for translational equilibrium for horizontal components of force
  42. M

    Calculate Equilibrium Temperature

    Homework Statement A 1kg of ice at -30° C is added to 10 kg of steam at 500°C. answer the following questions: a) What is the final phase of the system of ice + steam if no heat escaped from it. b) What is the final temperature when the equilibrium is established Homework Equations...
  43. D

    Equilibrium in Newtonian Mechanics: What is the Connection to Lagrangians?

    So let's say we have a mechanical system described by some Lagrangian L=L(q_i,\dot{q}_i), where the qi's are the generalized coordinates of the system. Does the condition \frac{\partial L}{\partial q_i}=0 give the equilibrium configurations of the system? Intuitively it seems so, but I can't...
  44. J

    How Do You Calculate the Mass of an Asymmetrical Ruler in Equilibrium?

    Homework Statement Suppose the ruler in procedure 3 is asymmetrical, balancing at the 60.2 cm mark. The ruler is now supported at the 41.3 cm mark, and a mass of 364 g is placed at the 26.2 cm mark. Find the mass of the ruler. The ruler is 1.00 m long. Homework Equations...
  45. S

    Exploring Frictional Forces & Rotational Equilibrium

    Homework Statement When I drag my feet on the ground (on a frictionless surface), there will be an equal but opposite force acting on another body. What is that body exactly?Homework Equations none The Attempt at a Solution Will it be transferred to some other parts to my body? So in space...
  46. T

    Static equilibrium with Youn modulus

    Homework Statement In Figure, a 103 kg uniform log hangs by two steel wires, A and B, both of radiuses 1.20 mm. Initially, wire A was 2.50 m long and 2.00 mm shorter than wire B. The log is now horizontal. What are the magnitudes of the forces on it from Wire A, and Wire B? Ysteel= 2.00*10^(11)...
  47. T

    How Far Can a Painter Walk on a Plank Before It Tips?

    Homework Statement A painter (mass 61 kg) is walking along a trestle, consisting of a uniform plank (mass 20.0 kg, length 6.00 m) balanced on two sawhorses. Each sawhorse is placed 1.40 m from an end of the plank. A paint bucket (mass 4.0 kg, diameter 28 cm) is placed as close as possible to...
  48. D

    Simple Harmonic Motion and equilibrium

    Homework Statement A 93-kg box hangs from the ceiling of a room—suspended from a spring with a force constant of 540 N/m. The unstressed length of the spring is 0.505 m. (a) Find the equilibrium position of the box. (b) An identical spring is stretched and attached to the ceiling and the box...
  49. B

    Measurning the partial pressure of a component of a solution in equilibrium

    Homework Statement Suppose I have two substances in a solution, each forming an equilibrium with its corresponding vapor phase, and thus having its own partial pressure. How can I measure this partial pressure of one of the components, given the pressure of each component in its pure form...
  50. M

    Time to Equilibrium: Reactants vs Products

    Is the time taken to reach equilibrium the same whether starting from reactants or products, under the same conditions? I think intuitively it is but cannot find a reference or proof.
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