The third law of Newton is always fulfilled?

In summary, the conversation discusses whether or not Newton's third law applies in the case of two charged particles moving in perpendicular directions. While it is agreed that the law applies in terms of the electric field, there is disagreement about whether it also applies to the magnetic field. Some argue that the force exerted by the magnetic field of one particle on the other does not equal the force exerted by the other particle's magnetic field, leading to a violation of the third law. Others argue that both the electric and magnetic fields must be considered and the third law still holds.
  • #1
chuy
31
0
Is certain that this law not fulfilled in the case of two charged particles moving in perpendicular directions (the force exerted in the particle A by the magnetic field of B is not equal to the exerted one in B by the magnetic field of A) ? Why?

Bye!
 
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  • #2
Why do you think it wouldn't hold?
 
  • #3
of course it is

How would the third law not apply? Sure, the particles would have motion different than uncharged particles, but if you consider the magnetic and electrical forces, everything works.
 
  • #4
Indeed Newtons 3. law fails this situation. If you have 2 charged particles moving perpendicular like in the following config.

A
*->

* B
| (x) [itex]\mathbf{B}[/itex]
v

You can look at it as currents in those directions. Then A will create a magnetic field given by the righthand rule. The direction of the B-field from A at B is as shown into the page (x). If particle B (with a charge q) have the velocity [itex]\mathbf{u}[/itex], then the force on B from A will be

[tex]\mathbf{F}=q(\mathbf{u}\times\mathbf{B})[/tex]

But there is no magnetic field from the charge B at exactly that spot of A, so there won't be a force from B acting on A there, but there is a force acting on B from A. And here is the failure of Newtons 3. law.
 
  • #5
What about the electric field?
 
  • #6
wxrocks said:
What about the electric field?
Newton's third law certianly applies here.
 
  • #7
Then, if we also consider electric field, Isn't violated the law? How?

Greetings!
 
  • #8
There will be an electric field not matter what, otherwise it wouldn't be called an electric charge. But there will also be a magnetic field if they are moving, with an electric field, obeying the 3rd law of Newton, but it's the force due to the magnetic field that fails the 3rd law.
 

Related to The third law of Newton is always fulfilled?

1. What is the third law of Newton?

The third law of Newton, also known as the law of action and reaction, states that for every action, there is an equal and opposite reaction. This means that when a force is exerted on an object, the object will exert an equal and opposite force back on the source of the original force.

2. How is the third law of Newton relevant in everyday life?

The third law of Newton is relevant in everyday life because it explains many common experiences, such as the recoil of a gun when fired or the movement of a rocket. It also helps us understand how objects interact with each other and how forces can affect motion.

3. Is the third law of Newton always fulfilled?

Yes, the third law of Newton is always fulfilled. This means that in any given interaction between two objects, the forces they exert on each other will always be equal and opposite. It is a fundamental law of physics and has been proven through countless experiments and observations.

4. Can the third law of Newton be violated?

No, the third law of Newton cannot be violated. It is a fundamental law of nature and has been observed to hold true in all situations. If it were to be violated, it would contradict our understanding of how the physical world works.

5. How does the third law of Newton relate to conservation of momentum?

The third law of Newton is closely related to the concept of conservation of momentum. This is because the equal and opposite forces described by the third law result in an exchange of momentum between interacting objects. This exchange of momentum ensures that the total momentum of a system remains constant, in accordance with the law of conservation of momentum.

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