Newton's third?

[ACUV]

Newton's third law states that action and reaction are equal and opposite. In the realm of Non Newtonian Physics, is it possible to exert a force without there being any equal and opposite of that force?

[ajb]

For example, the electromagnetic field can carry energy and momentum and so we can have violation of third law.

[illuusio]

For example, the electromagnetic field can carry energy and momentum and so we can have violation of third law.

 

How come? I mean first of all, electrons orbiting nucleus weaken the strong interaction's ability to keep nucleus in one part. Second, magnetized material crystal can be demagnetized. To me that tells magnetic field experiences third law.

[ajb]

In short, in electrodynamics the electromagnetic field "induces" a time delay into the motion: The EM field carries momentum at a finite speed. This already makes Newton's third law very unclear as it assumes instantaneous action of the forces between a pair of bodies. In electrostatics, you do still have Newton's laws.

 

 

However we still have conservation of energy and momentum in electrodynamics, which is today understood as being far more fundamental than the notion of a force. In modern theoretical physics force is not a central concept, symmetries and conservation law are.

[illuusio]

In short, in electrodynamics the electromagnetic field "induces" a time delay into the motion: The EM field carries momentum at a finite speed. This already makes Newton's third law very unclear as it assumes instantaneous action of the forces between a pair of bodies. In electrostatics, you do still have Newton's laws.

 

 

However we still have conservation of energy and momentum in electrodynamics, which is today understood as being far more fundamental than the notion of a force. In modern theoretical physics force is not a central concept, symmetries and conservation law are.

 

Very nicely answered

[EquisDeXD]

For example, the electromagnetic field can carry energy and momentum and so we can have violation of third law.

 

Wait, I was thinking about that myself, but I specifically remember seeing from a scientific text book that when an electro-magnetic field exerts a repulsive force on another object that the other object exerts the same force, this has to be true because if you push on a wall, it pushes back with the same force, but both you and the while are composed of atoms, and those atoms repel each other which is why you don't push the wall down, it's also the reason why all matter doesn't just automatically collapse to the lowest possible energy state and form black holes, because there's electro-magnetic repulsion between atoms that exert the force needed to keep objects up. So, if you push on the wall and it pushes back with the same force, and the mechanism for the force equivalence is an electro-magnetic field, then it should be logically concluded that an electro-magnetic field does not violate the third law when carrying momentum, so how exactly does it violate the third law? You mentioned a time delay, but how does that mean the same amount of force isn't eventually transferred?

Edited October 15, 2012 by EquisDeXD

[ajb]

Wait, I was thinking about that myself, but I specifically remember seeing from a scientific text book that when an electro-magnetic field exerts a repulsive force on another object that the other object exerts the same force, this has to be true because if you push on a wall, it pushes back with the same force, but both you and the while are composed of atoms, and those atoms repel each other which is why you don't push the wall down, it's also the reason why all matter doesn't just automatically collapse to the lowest possible energy state and form black holes, because there's electro-magnetic repulsion between atoms that exert the force needed to keep objects up. So, if you push on the wall and it pushes back with the same force, and the mechanism for the force equivalence is an electro-magnetic field, then it should be logically concluded that an electro-magnetic field does not violate the third law when carrying momentum, so how exactly does it violate the third law? You mentioned a time delay, but how does that mean the same amount of force isn't eventually transferred?

 

Newton's third law is obeyed in electrostatics, the same as it is in Newtonian gravity (with two bodies anyway). The stability of matter requires quantum mechanics, where again Newton's laws become obscure.