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

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Discussion Overview

The discussion explores the relationship between Newton's Third Law of Motion and magnetic forces, particularly in the context of electric motors and the behavior of charged particles in magnetic fields. Participants examine theoretical aspects, practical examples, and the underlying physics of magnetism.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Homework-related

Main Points Raised

  • Some participants suggest that the Third Law relates to momentum conservation, which applies generally but is less obvious in magnetic interactions.
  • One participant claims that magnetic forces can appear to violate the Third Law, necessitating the consideration of electromagnetic fields having momentum.
  • There is a discussion about the nature of magnetic forces, with some asserting that magnetism is well-understood as a force exerted on moving charges.
  • Participants question the specifics of how magnetic forces operate, comparing them to other forces like water pressure on objects.
  • Some responses emphasize the role of photons in electromagnetic interactions, suggesting that particle exchanges occur in the context of magnetic forces.
  • There is a call for more specific examples regarding the movement of electrons in magnetic fields to clarify the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between the Third Law and magnetic forces, with some asserting connections while others highlight apparent violations. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants express uncertainty regarding the fundamental nature of magnetic forces and their relationship to other physical phenomena, indicating a need for clearer definitions and examples.

Who May Find This Useful

This discussion may be of interest to those studying electromagnetism, physics students seeking clarification on fundamental concepts, and individuals curious about the interplay between classical mechanics and electromagnetic theory.

magmash
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Hi

does the Third law of motion have any thing to do with the magnetic force

like in a electric motor ?
 
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The 3rd law on the general level means momentum conservation, which always applies. In the case of magnetic interactions it is sometimes less obvoius. Do a search on 'recoil of a railgun'.
 
Welcome to PF;
The short answer is "yes".
Did you have a specific example in mind?
 
Well the magnetic force violates the third law, hence it was recognized that the electromagnetic field itself must also have momentum to compensate and conserve momentum in the system.
 
Simon Bridge said:
Welcome to PF;
The short answer is "yes".
Did you have a specific example in mind?

Yes

The movement of electrons
 
I am not able to find any information on what the magnetic force really is
Is it some thing that science can't really explain at the mean time, like example what exactly causes Gravity
 
magmash said:
I am not able to find any information on what the magnetic force really is
Is it some thing that science can't really explain at the mean time, like example what exactly causes Gravity

No the theory of magnetism has been around for a long time, and so has the theory of gravitation.
Magnetism is just a force exerted on moving charges by other moving charges. (Or if you're into that magnetic monopole stuff, magnetic charges as well)
 
any more info ?
 
The magnetic force is part of the electromagnetic force - which is understood, in the standard model, in terms of interactions between charged particles, such as electrons, and photons. You should look up "quantum electrodynamics".

note: "movement of electrons" is too vague - can you be specific?
i.e. can you think of some situation in which the motion of an electron in a magnetic field appears to violate the third law?
 
  • #10
Simon Bridge said:
The magnetic force is part of the electromagnetic force - which is understood, in the standard model, in terms of interactions between charged particles, such as electrons, and photons. You should look up "quantum electrodynamics".

note: "movement of electrons" is too vague - can you be specific?
i.e. can you think of some situation in which the motion of an electron in a magnetic field appears to violate the third law?

Well what I mean is,

example when we spray water at an object let's say a standing piece of plywood, the ply wood will fall down due the the force of the water particles hitting the plywood, Well how does the magnetic force work ? is there any atom,particle collisions causing the force ?
 
  • #11
magmash said:
Well what I mean is,

example when we spray water at an object let's say a standing piece of plywood, the ply wood will fall down due the the force of the water particles hitting the plywood, Well how does the magnetic force work ? is there any atom,particle collisions causing the force ?

Thre are four known forces, and the electromagnetic is one of those. When you spray water various forces come into play.

I suggest you read a high school textbook on electromagnetism http://en.wikipedia.org/wiki/Electromagnetism

If you do some simple experiments it becomes more obvious. eg electromagnets, deflection of a compass by current in a wire.
 
Last edited by a moderator:
  • #12
magmash said:
Well what I mean is,

example when we spray water at an object let's say a standing piece of plywood, the ply wood will fall down due the the force of the water particles hitting the plywood, Well how does the magnetic force work ? is there any atom,particle collisions causing the force ?
OK - so you don't want to talk about electrons then?

The principle is that a photon is transferred or exchanged between charges.
So the quickie answer to your question is "yes - there is a particle collision involved"... though, on the scale of photons, "collision" is not the right word...

See:
http://van.physics.illinois.edu/qa/listing.php?id=414
http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html

It is difficult to know how to answer your questions, or even what you are asking, properly, since you won't tell us where you are coming from. Presumably you have seen magnets work right? So what are you asking? What level are you asking from?
 

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