What is Third law: Definition and 377 Discussions

The third law of thermodynamics states as follows, regarding the properties of closed systems in thermodynamic equilibrium: The entropy of a system approaches a constant value as its temperature approaches absolute zero. This constant value cannot depend on any other parameters characterizing the closed system, such as pressure or applied magnetic field. At absolute zero (zero kelvins) the system must be in a state with the minimum possible energy. Entropy is related to the number of accessible microstates, and there is typically one unique state (called the ground state) with minimum energy. In such a case, the entropy at absolute zero will be exactly zero. If the system does not have a well-defined order (if its order is glassy, for example), then there may remain some finite entropy as the system is brought to very low temperatures, either because the system becomes locked into a configuration with non-minimal energy or because the minimum energy state is non-unique. The constant value is called the residual entropy of the system. The entropy is essentially a state-function meaning the inherent value of different atoms, molecules, and other configurations of particles including subatomic or atomic material is defined by entropy, which can be discovered near 0 K.
The Nernst–Simon statement of the third law of thermodynamics concerns thermodynamic processes at a fixed, low temperature: The entropy change associated with any condensed system undergoing a reversible isothermal process approaches zero as the temperature at which it is performed approaches 0 K. Here a condensed system refers to liquids and solids.
A classical formulation by Nernst (actually a consequence of the Third Law) is: It is impossible for any process, no matter how idealized, to reduce the entropy of a system to its absolute-zero value in a finite number of operations.
There also exists a formulation of the third law which approaches the subject by postulating a specific energy behavior: If the composite of two thermodynamic systems constitutes an isolated system, then any energy exchange in any form between those two systems is bounded.

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  1. davidbenari

    Newton's third law in ropes and tension

    For some reason I couldn't answer this, and I hope you can help me: a) Two people pull on a rope, one with 200 N , the other 100 N. Why is the tension on the rope the shared magnitude of both forces? b) If two people pull on a rope with equal force (say, 100 N), each person pulling feels...
  2. kelvin490

    Gibbs equation and third law of thermodynamics

    I have seen a discussion of what would happen for an ideal gas expands irreversibly and adiabatically until absolute zero degree K. The entropy change is like that: Δs=Cv ln(T2/T1)+R ln(V2/V1) It is impossible for T2 to be zero K in the equation and so it becomes one justification of the...
  3. BrainMan

    How Can You Calculate Jupiter's Mass Using Callisto's Orbital Data?

    Homework Statement The planet Jupiter has at least 14 satellites. One of them, Callisto, has a period of 16.75 days and a mean orbital radius of 1.883 x 109 m. From this information, calculate the mass of Jupiter. Homework Equations T2 = (4∏2/ GM)r3 ∏ = pi The Attempt at a...
  4. S

    Newtons third law and quantum mechanics

    dear sir, we know that third law of motion says that every action has a equal and opposite reaction. quantum mechanics tells us that it is possible not predict the position as well as the speed of electron. i like to know if electrons ,protons and neutrons form a system called atom...
  5. P

    Can a change in units cancel out G/4π2 in Kepler's third law?

    For two two bodies of mass M1 and M2 in circular orbits of radius a1, a2 about their common centre of mass, the Newtonian modification of Kepler's third law is a3/P2=G(M1+M2)/4π2. Where a=a1+a2. The problem is that I have been told that when using the units of years, solar masses and...
  6. A

    Solving Newton's Third Law: Where Am I Going Wrong?

    Please look at picture. Here are my equations: For 10kg: -uk m2 g cosθ -T -m2 g sinθ=m2 a For 20kg: T-m1 g =m1 a Add them: -uk m2 g cosθ -m2 g sinθ -m1 g =(m2+m1) a a= 5 m/s^2 (kinematics equations) Isolating uk gives 3.66! The real answer is 0.16. Where am I going wrong?
  7. P

    Newton's Third Law and Linear Momentum Conservation

    I have always been under the impression that Newton's third law and the law of conservation of linear momentum are really the same thing; synonymous, so to speak. But then I was wondering if Newton's Third Law holds for a non-isolated system. I mean, I know for sure that momentum conservation is...
  8. R

    Newton's Third Law and the Conservation of Momentum

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  9. Conservation

    Conceptual problem on Newton's Third Law

    Newton's Third Law states that for every action force, there is a reaction force. So take a classical problem with a basketball player. The Earth has a gravitational force on the player, and thus player exerts an equal and opposite force on the earth. The player is stationary. My first...
  10. K

    Solving Kepler's Third Law for Period - 6.7E6m

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  11. H

    Chain Link Problem? [Tension Forces; Newton's Third Law]

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  12. O

    Newton's Third Law Problem [Checking Solution]

    Homework Statement Two hockey players are standing stationary on the ice facing one another. Player A has a mass of 85kg and Player B is 110kg. They shove each other and player A ends up with a velocity of 1.5m/s [W]. Find the final velocity of Player B. Solution Fa=Maaa Fa=(85)(1.5-0/t)...
  13. S

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  14. O

    Solve Third Law Problem: 833N Diver from 375kg Boat w/ 2.25m/s Velocity

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  15. O

    Calculating Acceleration and Velocity in Newton's Third Law Scenario

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  16. 0

    Newton's Third Law of a car and truck

    I have a question for which I am intensely confused. Lets say a car was pushing a big truck from behind. And the car (and truck) are accelerating, then there is a breakdown because the car applies all the force it has to the truck, which pushes back with equal force. So the car shouldn't be...
  17. N

    Newton's Third Law and Unbalanced Forces

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  18. N

    Newtons third law question- Action reaction pair

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  19. B

    Newton's third law and energy transfer

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  20. C

    Coulomb's Third Law of Friction

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  21. S

    Does SR and GR agree on Newton's Third Law of Motion ?

    Sorry guys not a physicist!Only wish to know if there is agreement between Newton laws of motion and SR/GR in particular?I know these two don't match in some cases? What are they in simple words please!? Cheers
  22. W

    Is Maxwell's third law the proof of conservation of energy in E&M?

    Hello! When studying the law I noticed that the change in magnetic field (i.e the magnet's motion) is = to the EMF induced. That proofs to me how the principle of the conservation of energy is applied to the world of electromagnetism as well! The energy applied to move the magnet is...
  23. M

    Third Law of Motion and Magnetic Force: Is There a Connection?

    Hi does the Third law of motion have any thing to do with the magnetic force like in a electric motor ?
  24. G

    Radiation reaction force and Newton's third law

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  25. S

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  26. V

    How Do Newton's Third Law and Force Calculations Apply to Hockey Players on Ice?

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  27. D

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  28. M

    Newton's third law, bullet through wood question

    1. A 0.0048kg pullet traveling with a speed of 200m/s penetrates a large wooden fence post. If the average resisting force exerted on the bullet was 4500N how far did the bullet penetrate. 2. F=ma? 3. F = ma F/m = a 4500/0.0048 = 937500? So there's a reverse acceleration of...
  29. B

    Calculating Take-Off Speed Using Newton's Third Law

    question is 29./ about bob and throwing his rock, I have found a./ (225N) easily enough it is b./ which i cannot figure out. I am assuming that it is a Newtonian action-reaction pair and that the rock pushes back on bob at 225N as well, which would mean Bob's acceleration would be 3.0ms/s^2. But...
  30. A

    Newton's third law in terms of inertial position vectors for n-body system

    Assuming $$\vec{r_{a}}$$ and $$\vec{r_{b}}$$ is calculated from an inertial frame of reference. then for any two objects (named a and b) in a system of more than two objects, Is this the Newton's third law, $$\frac{d^{2}}{dt^{2}}m_{a}\vec{r_{a}}=-\frac{d^{2}}{dt^{2}}m_{b}\vec{r_{b}}$$...
  31. M

    Questions on work done and Newton's third law

    Hello 1- work done to push body forward is greater than to pull body backward what is the explanation for this?can you draw the two FBD in both cases ? 2- why is nail driven in wooden wall but not in the concrete wall ؟ I guess this is somehow related to Newton's third law Thanks
  32. B

    Newton's Third Law Explanation

    For every force exerted by object A on object B, an equal and opposing force is exerted by object B on object A. I need help understanding the principle. I understand it when dealing with a completely stationary object: pushing on a solid wall, it exerts an equal force back to your hand...
  33. S

    How Do Forces on a Cantaloupe and Table Change in an Accelerating Elevator?

    Homework Statement Suppose you have a cantaloupe (C) on a table (T). Let FTC be the force on the table by the cantaloupe, and let FCT be the force on the cantaloupe by the table. Do the magnitudes of these forces increase, decrease, or stay the same if they are placed in an elevator which...
  34. O

    Solving for Force of B on A in a Newton's Third Law Problem

    Homework Statement Two Blocks, A (10kg) and B (12kg) are placed next to each other on a rough surface. An applied force acting on block A causes both blocks to accelerate at 1.2m/s^2 to the right. If the magnitude of the force of friction on Block B is 18.3N, calculate the force (magnitude and...
  35. P

    Newton's third law and a motor

    hey people,greetings to everyone i'm an freshman in physics so i have some problems understanding Newton's third law. for example how can a motor accelerate an elevator upward,or downward?i know Newton's third law acts on different objects,i understood the house and the cart problem. horse is...
  36. M

    Newton's Third Law and acceleration question

    Two wrestlers are pushing each other. Initially the wrestlers are at rest, however the small wrestler starts to move. Now in either cases, which wrestler exerts more force? My professor said that both exert the same amount of force on each other. This is really confusing as if they are applying...
  37. P

    Making sense of Newton's Third Law

    This is going to be a stupid question, for which I apologize. I am probably over-thinking things but my reasoning is flawed somewhere because when I think about Newton's Third Law and it's application to real-world examples, I can't understand how objects move at all, whether accelerating or...
  38. D

    Find Pluto's year length using Kepler's third law.

    Homework Statement Pluto is 40 times further from the Sun than we are. How long is a year on Pluto? (Use Kepler's third law.) Homework Equations 4∏^2/Gm=T^2/r^3 The Attempt at a Solution Te^2(Earth period)=x*r^3 Tp^2(Pluto period)=x*(40r)^3 I don't know what to do...
  39. D

    Validating Third Law of Thermodynamics

    1) Does anyone have a general idea of how to experimentally validate or falsify the Third Law of Thermodynamics in its strong form? In another thread, I suggested a procedure for validating the third law of thermodynamics in its weak form. Basically, one determines the specific heat...
  40. A

    Is Newton's Third Law a Manifestation of Fundamental Laws?

    Sometimes I wonder if it actually possible to prove the action-reaction principle. I do know that Newtons laws are empirical but then if you think about the third law it says that in interaction between two bodies they exert equal and opposite forces on each other. Now what happens in the...
  41. V

    A couple of gravitational problems (kelper's third law)

    Homework Statement A satellite is to be placed in orbit about the Earth at an altitude of 1.6 x 10 6m. What will be its period of motion? The answer is 7.2x 103s 2. The attempt at a solution Using kelper's third law. R3 / T2 = R3 / T2 Radius of satellite: 6.38 x 106 + 1.6 x 106...
  42. M

    Third Law of Motion :Confusion

    When we push a body say for example,a crate on ground.Then in response to our force the crate also exerts a force on our hands.Then my question is why does the crate move forward and not we that move backward?
  43. L

    Exploring the Pain of Board Breaking: A Newton's Third Law Analysis

    Hi all, I have a general question about board breaking. This is not homework. Can anyone explain why it hurts more not breaking the board, compared to breaking the board. I know that there are already threads about this topic. However, I am confused about the different explanations: 1...
  44. S

    Newton's Third Law Explained: Is it for Cushions?

    Please anybody explain me ... if i punch a soft cushion hardly say "F" force will thw cusion hurt me with the same ... every body says "NO" ok all right everybody says "you, in this case have not applied the "F" force because most part of it is wasted in changing the shape of cusion " so here...
  45. P

    The meaning of force and Newton's third law

    I push on a wall and the wall pushes me back (according to Newton's third law), but what i don't understand is that no acceleration is produced hence is it not that i have not applied any force? If i jump then i return to the ground (obviously) then doesn't the Earth accelerate towards me...
  46. cryora

    Does Newton's Third Law apply to magnetism?

    Newton's Third Law states that every action has an equal and opposite reaction. I'm wondering if and how this applies to magnetism. I would assume that it would mean if a moving charge is creating a magnetic field that causes a magnetic force on another charge, then it can be said that the...
  47. S

    Newton's third law when moving our body

    Homework Statement When I push my belly forward, a force is exerted on my belly by my muscles. So there will be a reaction force acting on the muscles right? But eventually it has a net forward force. So if we treat the belly as one object (muscle fat everything in the belly) then where is the...
  48. E

    Hw can we relate conervation of momentum with Newton's third law?

    Hw can we relate conervation of momentum with Newton's third law?? Hw can we relate conervation of momentum with Newton's third law??.. Quantitavely and qualitatevely i want a clarification for the realation between these.. Assume an apple falling towards earth.. Thanks in advance
  49. M

    Why Does a Book on a Table Stay at Rest Despite Action and Reaction Forces?

    Action and reaction do not balance each other.But then why a book lying on a table lies at rest?The reaction force and the gravitational force cannot balance each other.Then how is it?
  50. D

    Newton's Third Law: Why Does Motion Occur?

    Newton third law! Hi fellow members! I would like to ask a silly question because my basic concepts are quit weak. Since according to Newton third law, with every action, an opposite and Equal force react to resist motion.Since both ACTion and Reaction forces are equal, they will cancel each...
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