Equilibrium Definition and 1000 Threads

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. Mason Smith

    Find the displacement from equilibrium after some time

    Homework Statement A 50 lb weight is attached to the end of a spring. The spring is stretched 6 inches. Find the displacement from equilibrium of the weight after (π/8) seconds, if the weight is released from a point 2 inches above the equilibrium position. Round to the nearest length of a...
  2. Andres Padilla

    FBD of an aerogenerator (Windmill)

    Homework Statement Good afternoon, I hope someone could help me with this problem, it is killing my head. I have an aerogenerator, I already find the torque excerted by the air (75.8N) and the force transmitted by the gear (1010.6N). The problem comes when I try to draw the free body diagram to...
  3. A

    Quick clamp wedge/friction lock calculation

    I am currently working on designing a linear brake/lock for a completely different purpose but it will be based on the same principle as in a quick clamp shown below. Before building a prototype I do want to make some rough calculations to check dimensions, angles etc. etc. However, I am for...
  4. C

    I Activity of daugther isotope in secular equilibrium

    Consider chain of two radioactive decays ##A \to B\to C##. The equation that regulates ##N_B## is $${\frac {\mathrm {d} N_{B}}{\mathrm {d} t}}=-\lambda _{B}N_{B}+\lambda _{A}N_{A}$$ I can't understand why the activity of ##B## is get as ##\lambda_B N_B##, for example at page 20 here...
  5. S

    How Does Increased Pressure Affect Chemical Equilibrium in the Reaction A⇔2B?

    Homework Statement Consider the reaction : A⇔2B (⇔ stands for reversible). 1 mol of A and 2 mol of B are taken in a closed container at equilibrium. Suppose the pressure is increased, how much of B (by moles) will decompose to restore equilibrium ? Homework EquationsThe Attempt at a Solution...
  6. A

    Finding Equilibrium in Electric Fields of Two Charges

    Homework Statement An electric field is created by an uniform linear charge with a linear charge density is 40 nC/m. Find the potential difference between the two points, one of which is situated 5 cm from the line charge and the second at 10cm. Two charges, q and -3q, are situated at a...
  7. P

    Thermal equilibrium in open systems

    Is it possible for an open system to reach thermal equilibrium? why/why not?
  8. Z

    Equilibrium: Le Chatelier's Principle and CaCO3 Decomposition

    Homework Statement I had a question on a test and I got the wrong answer, but I still don't understand why. It was a Le Chatelier problem about the equilibrium shift, and it described the decomposition of CaCO3 CaCO3(s) <->CaO(s) + CO2(g) The question asked something along the lines of "If...
  9. J

    For a solution that contains 0.10 M HCN and 0.10 M NaCN, whi

    Homework Statement >For a solution that contains 0.10 M HCN and 0.10 M NaCN, which statement is false? A) This is an example of the common ion effect. B) The [H+] is larger than it would be if only the HCN was in solution. C) the [H+] is equal to $K_a$ D) Addition of more NaCN will shift...
  10. thevinciz

    Equilibrium of a stiff plate on inclined planes

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  11. B

    Proof of oscillation about the equilibrium

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  12. J

    Proving stable equilibrium: Rotating circular hoop

    Homework Statement A circular hoop of radius R rotates with angular frequency ω about a vertical axis coincident with its diameter. A bead of mass m slides frictionlessly under gravity on the hoop. Let θ be the bead’s angular position relative to the vertical (so that θ = 0 corresponds to the...
  13. SmamMir

    System of equilibrium, why won't the normal force apply?

    Homework Statement Homework EquationsThe Attempt at a Solution I've resolved all the relevant forces (tension, weight, normal force), but upon looking at the mark scheme, there is no normal force to be resolved. Forgive me if I'm missing out on something obvious, but shouldn't there be a...
  14. thevinciz

    Finding Equilibrium of Forces: A Shortcut Method

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  15. B

    Why are the angles in rope equilibrium the same?

    Homework Statement Between two parallel walls we tighten a rope. One end of a rope is tied a little higher on the wall than the end on the opposite wall. On the rope we put a pulley with mass m which slides to equilibrium position. Homework EquationsThe Attempt at a Solution I assumed that in...
  16. Leonardo Machado

    A Beta equilibrium for free and interacting nucelar models

    Good evening. I'm currently studing dense matter and nuclear matter above 10^8 g/cm^3, and i know well how to insert a beta equilibirum condition in a free Fermi gás at T=0. \sqrt{K^2_{F,n}+m^2_n}=\sqrt{K^2_{F,p}+m^2_p}+\sqrt{K^2_{F,e}+m^2_e} But how do i insert the same condition of...
  17. Marcin H

    Semiconductors - Flat band Diagram vs Equilibrium Diagram

    Homework Statement Homework Equations Energy band diagram equations. The Attempt at a Solution This is more of a conceptual question, but this is the problem I am working on for reference. What is the difference between a flat band diagram and an equilibrium diagram? I know what they will...
  18. K

    Thermodynamics equilibrium with respect to matter flow

    Homework Statement I don`t know if the image will show so I`m also adding a link to the image of the problem. This problem is a modification my professor made to the one in the link below(*), he changed the rigid diathermic partition into a movable partition. I`m supposed to find the...
  19. lfdahl

    MHB Fish Pond Challenge: Show Equilibrium Variation with $R_f$

    Suppose a pond contains $x(t)$ fish at time $t$, and $x(t)$ changes according to the DE: \[\frac{\mathrm{d} x}{\mathrm{d} t} = x\left ( 1-\frac{x}{x_0} \right )-R_f\] where $x_0$ is the equilibrium amount with no fishing and $R_f > 0$ is the constant rate of removal due to fishing. Assume $x(0)...
  20. HappyFlower

    Can you find the total vertical force acting on this rod?

    Homework Statement I am trying to understand which forces are up or down and left and right. I am trying to also find out the torque that would be clockwise and counterclockwise on the figure. Homework EquationsThe Attempt at a Solution Original Picture Edited Picture Arrows indicate...
  21. lc99

    Question About a 3D Equilibrium Problem

    Homework Statement Homework EquationsThe Attempt at a Solution rxF I'm trying to find the moment of the 50lb about the x,y,z axes. So, i did the vector from the origin to the top of the larger wheel crossproduct with the force vector of 50. Thus, Vector Origin to Wheel x F vector = (0.2i...
  22. lc99

    What Are the Forces Needed to Hold a Wheelbarrow at a 30∘ Angle?

    Homework Statement The wheelbarrow and its contents have a mass of m = 63 kg with a center of mass at G. Determine the normal reaction on the tire and the vertical force on each hand to hold it at θ = 30∘. Take a = 0.27 m , b = 0.43 m , c = 0.78 m and d = 0.10 m . (Figure 1) Homework...
  23. R

    Finding a maximum force in a beam type system before failure

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  24. E

    Cube balanced at equilibrium about two different axes

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  25. Brilli

    An equilibrium problem -- Spinning a hinged rod and a ball

    Homework Statement This is a practice olympiad problem A light rod with length l is hinged in such a way that the hinge folds in one plane only. The hinge is spun with angular speed ω around a vertical axis. A small ball is fixed to the other end of the rod. (a) Find the angular speeds for...
  26. H

    I Some help with deriving svedberg equilibrium equatio please

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  27. Richie Smash

    Find the maximum length of x that will maintain equilibrium

    https://www.physicsforums.com/attachments/220647 Homework Statement Two uniform planks each of mass 10Kg and length 2m, are arranged as shown in the picture. Find the maximum value of x for which the top plank will remain in equlibrium. Homework Equations F= (mgl)/hThe Attempt at a Solution I...
  28. T

    Complete Motion of a ball in a Stable Equilibrium

    Hello Everybody! My name is TanX and I got a figure in my mind while studting concepts related to Vertical Circular Motion. I tried finding a solution to it (i.e) I tried finding the condition for movement of the particle in the figure that had come in my mind... Homework Statement So here is...
  29. S

    Thermodynamics equilibrium constant problem

    Homework Statement N2 + 3H2 --> 2NH3 (all gases) Why is such a high pressure needed? Calculate the equilibrium constant at 500k then estimate the percentage conversion at equilibrium at 1 bar total pressure, assuming the stoichiometric ratio of N2:H2 is 1:3. Repeat the process at 50 bar...
  30. J

    Equilibrium of an object orbiting around a planet

    Homework Statement Homework EquationsThe Attempt at a Solution Honestly , I have not been able to understand the question . I am totally clueless about the part written in parenthesis . All I understand is that since the length of the rod is not negligible ,value of gravity at the location...
  31. D

    What Is the Formula for Calculating Thermal Stabilization Time?

    Hello all. Been a long time since I took a thermal course. I'm looking for a formula to work with the thermal stabilization of something. Specifically, I want to minimize the time required for thermal stabilization to occur and how to mathematically calculate what that set temperatures should...
  32. Zack K

    Weight of an object in static equilibrium

    Homework Statement An object is suspended on a frictionless slope inclined plane by a rope parallel to the incline. If the angle of the incline is 25° and the tension on the rope is 5000 N, what is the weight of the object Homework Equations ∑F=0 The Attempt at a Solution So in my eyes, you...
  33. Zack K

    Mass of a picture in static equilibrium

    Homework Statement An artist must push with a minimum of 75N at an angle of 45° to a picture to hold it in equilibrium. The coefficient of friction between the wall and the picture frame is 0.30. What is the mass of the picture? Homework Equations ΣF=0 Ffr=μFN F=ma The Attempt at a Solution I...
  34. J

    Torque and Rotational Equilibrium with a slanted Rod/Cable

    Homework Statement There is a lever rod of length 3.43 m, weight 44 N and uniform density. The lever rod is pivoted on one end and is supported by a cable attached at a point 0.902 m from the other end. The lever rod is in equilibrium at angle of 68◦ from the vertical wall. The cable makes...
  35. Emanuel0406

    How Can I Solve This Static Equilibrium Problem?

    Hello! I was wondering if anyone could give me a hand with the following problem. I am stuck and I don't know how to solve it. You can see attached the problem and my work so far. Thank you very much for your help.
  36. Emanuel0406

    Solve Static Equilibrium Problem: Get Help Now

    1. The problem statement, all variabHello. I uploaded a picture with the problem that concerns me. As you can see from my work so far...I have tried to solve the problem but I'm stuck. I have tried a few times and I'm starting to question myself if the problem is correct or not. Please give me a...
  37. NFuller

    Statistical Mechanics Part I: Equilibrium Systems - Comments

    Greg Bernhardt submitted a new PF Insights post Statistical Mechanics Part I: Equilibrium Systems Continue reading the Original PF Insights Post.
  38. K

    Unstable equilibrium, centre of mass problem

    Homework Statement Two masses, A and B, are placed on the edges of a mass of 20 kg which is homogeneously distributed figure such that an unstable equilibrium is achieved. If the mass of A is 12 kg and the mass of B 16 kg, how large is the distance x from the left end of the board to the...
  39. L

    Equilibrium of forces (angle of road so car will not skid)

    Hi everyone. Our mechanics professor warned us that in the mid-term exam some students reached the right answer on some questions but their method was wrong. For this reason sometimes I'm worried when I reach the correct answer but the way I did it is different from the solution guide. And I...
  40. L

    Rotational equilibrium problem (ladder against a wall)

    Hi everyone, Our professor gave us a bunch of solved problems to practice with before the exam, and this one I'm struggling with: I'm trying to work through the solution step by step, and I get stuck at the point (3). What I understand is that we want to get the value of RH, which is...
  41. L

    Equilibrium with moments of forces

    Hi everyone, This is not really a homework question per se since it's not an assignment. Basically, our physics professor gave us a 100+ page syllabus filled with example questions and solutions and I am practicing with them by doing them one after the other. This one question I'm having...
  42. VSayantan

    Energy of a Gas in equilibrium with BB-radiation

    Homework Statement A closed, thermally-insulated box contains one mole of an ideal monatomic gas G in thermodynamic equilibrium with blackbody radiation B. The total internal energy of the system is ##U=U_{G}+U_{B}##, where ##U_{G}## and ##U_{B} (\propto T^4)## are the energies of the ideal gas...
  43. C

    MHB Can You Solve for Tension and Force in Static Equilibrium for a Boom?

    The uniform boom shown below weighs 668 N, and the object hanging from its right end weighs 386 N. The boom is supported by a light cable and by a hinge at the wall. Calculate the tension in the cable and the force by the hinge on the boom (both in N). (Enter the magnitudes.) Tension in the...
  44. L

    B De Sitter Equilibrium: Could it Exist in Heat Death?

    https://arxiv.org/pdf/hep-th/0405270.pdf I was reading this paper where ideas presently originally by Dyson, Kleban, and Susskind about de Sitter equilibrium have been expounded by the authors. I have a few specific questions. 1. Could de Sitter space exist, for instance, in the heat death of...
  45. Revengeance

    Concentration of Ions at Equilibrium

    Homework Statement Find the concentrations of all ions in the solution at equilibrium after 0.213 L of 0.433 M aqueous Cu(NO3)2 solution is mixed with 0.213 L of 0.120 M KOH solution. Ksp for Cu(OH)2 is 1.1E-15. Homework Equations n=m/M [Cu][OH]^2 = Ksp .. ?The Attempt at a Solution ok so for...
  46. S

    Find the mass in static equilibrium problem involving a spring

    Homework Statement Consider a rigid 2.60-m-long beam (see figure) that is supported by a fixed 1.30-m-high post through its center and pivots on a frictionless bearing at its center atop the vertical 1.30-m-high post. One end of the beam is connected to the floor by a spring that has a force...
  47. S

    Solving for Final Equilibrium Temperature of Water-Copper System

    Homework Statement 173 g of water at 20°C is contained in a copper container of mass 327 g. An additional 129 g of water at 100°C is added. What is the final equilibrium temperature (in degrees C) if we treat the system's water and container as isolated? Homework Equations Q = mcΔT The...
  48. D

    Chemical Kinetics: velocity and equilibrium

    Hi everybody, Given a generic reaction ## Reagents ↔ Products ## the velocity of the reaction is ##R = R_{right} - R_{left} ## To take in account that the velocity of the reaction will slow if approaching the equilibrium we say that $$ R = R_{right}(1 - \frac K K_{eq}) $$ Although it seems...
  49. F

    Solid-liquid Equilibrium via EOS

    Hi guys I want to model the adsorption of asphaltenes on nanoparticles from a thermodynamic equilibrium solution ( this is my thesis ). from this way, I want to show how much asphaltene is adsorbed on nanoparticles at different temperatures and pressures (without using of isotherms of...
  50. F

    Why am I getting 3 equations and 2 unknowns when summing moments about point A?

    What does it mean where it says it provides couples on x-axis and z axis? Anyways what am I doing wrong? my procedure is finding tension in cables by summing moments about point A. then with the tensions, finding reactions at A. However when i sum the moments about A I get 3 equations 2...
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