Question

When a magnet is placed in a non-uniform magnetic field! It feels a stronger force that accelerates it?! Does that mean newtons 3rd law is applicable? When I bring two magnets of the same magnetic field they would"repel". Now if I bring two magnet's one weaker then the other! It would be "repelled" greatly then ever because of the non-uniform mag.Field?!

@Hope99

Answer 1

It's easier to answer here.

Answer 2

Sure thing! :)

Answer 3

If we take a look at Coulomb's law:\[F_e=k_e \frac{|q_1||q_2|}{r^2}\]You can see that the magnitude of the force between the two point charges is the product of the magnitudes of the charges divided by the distance between the charges.

This means that the force on either charge is the same.

Answer 4

The force on either charge is the same in magnitude, that is.

Answer 5

So when a magnet is accelerated in a non-uniform magnetic field there is not change of force? Only change in acceleration?

Answer 6

The force is constantly changing, yes.

Answer 7

Coulomb's law doesn't apply here since we are dealing with magnetism. No matter your conclusion, though, the force between two particles will always be equal in magnitude.

I must go to sleep, though. I can discuss this more tomorrow.

Answer 8

Sure... In case of a charge F = the same.

However, in cause of magnets F= changing. Since its in a NON-UNIFORM field = GREATER So yea, pretty much go the right answers thanks @Xishem ! Hope you agree with what I'm saying.

Answer 9

So in case of a magnet placed in a magnetic field that is greater in strength or constantly changing, the magnet would experience a force that would be significant strong that will accelerate it and the force will change.



Simple example: Motor perhaps?

Thanks @Xishem for you're help I hope I got this right(Please due correct me if I'm wrong)

Answer 10

@Xishem how could you apply coulomb's law here? secondly, newton's third law talks about equal and opposite force...but here forces are unequal...and lastly if applied magnetic field is greater and of same polarity then for sure the magnet the magnet with weaker polarity will be repelled or you can say driven by magnetic force...of stronger one

Answer 11

well people - the Stronger field gradient is applied to Smaller magnet dipole, while the weaker field-gradient is applied to STRONGER dipole of the stronger magnet. REcall now, Mar HiShem that the force is proportional to the PRODUCT of Dipole\[\times Feld Gradient\] and you realize that the Forces are EQUALL in size.

Answer 12

By the way, though Coulomb force is unapllicable here in the "literary" sense, it IS a good analogy to the reason why forces are equall - just factor the forces int Field *Intensity of Dipole/Charge/Some property and you see the complete analogy.

Answer 13

Of course N's 3rd law is holding!

Field and field-gradient created by M1 is proportional to magnetic moment M1.
Force felt by M2 is proportional to M2.
Hence overall force acted on M2 by M1 is proportional to M1M2.

Field and field-gradient created by M2 is proportional to magnetic moment M2.
Force felt by M1 is proportional to M1.
Hence overall force acted on M1 by M2 is proportional to M2M1.

As M1M2 = M2M1, N's 3rd law holds.

Answer 14

Well - isn't it restatement of what I have explained ?

Answer 15

It is, but I was aiming at a conclusion with N's 3rd law which, I think, appears more clearly if certain quantities are highlighted and proved equal.

Answer 16

Yes but note the slightly philosophical reason for the original question. The Asker was seeking understanding of SEEMING inconsistency, or should I say seeming-contradiction.
So it is good in such cases to explain the Intuitive Factors of Nature interplay - not just the short formula. In fact the thirs law can be shown to be even the reason for the Second law - via the momentum conservation consequence. See Berkeley course on MEch

Answer 17

I meant Third law of Newton of course

Answer 18

"To every action there is always opposed an equal reaction: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts."

Note the : Mutual action "force" of two bodies. That means that two bodies with the same action = the same reaction.

In case of of a manget in a non-uniform magnetic field that is not! The same "action" force. There will not be a non equal reaction... @ghazi made perfect sense of that.

I do agree when two bodies of equal action act on each other there will be an opposite "equal" reaction. However, in a case of two bodies with different "actions" certainly the reaction will not be the same.

@Mikael @Vincent-Lyon.Fr @ghazi @Xishem .

Thats all based on my understanding of the Netwon's 3rd law and the Magnetism! Please correct me if I'm wrong. :)

Answer 19

Hope I stated out my last answer properly! Please tell me if its correct or not!
@Mikael @Vincent-Lyon.Fr @ghazi @Xishem !

Answer 20

When you are talking about a magnet in a non-uniform magnetic fields, you are only talking about one body.

Answer 21

"I do agree when two bodies of equal action act on each other there will be an opposite "equal" reaction. However, in a case of two bodies with different "actions" certainly the reaction will not be the same.
[...]
Thats all based on my understanding of the Netwon's 3rd law and the Magnetism! Please correct me if I'm wrong. :)"

Well, I have to correct you then because you are wrong ;-)

Two interacting bodies, whether similar or different (be they masses, charges, currents, electric moments, magnetic moments) do always have opposite action and reaction.

Answer 22

Yes. Your understanding of Newton's 3rd law is incorrect.

Answer 23

I guess so....
@Xishem Could you show me where I'm wrong?

"When you are talking about a magnet in a non-uniform magnetic fields, you are only talking about one body"

What if were 2 bodies? What would happen then?

Could you relate Newtons 3rd law to magnets please?

Answer 24

@Vincent-Lyon.Fr

"Two interacting bodies, whether similar or different (be they masses, charges, currents, electric moments, magnetic moments) do always have opposite action and reaction"

Could you clarify that more? Maybe an example could help?

Answer 25

if to object collided each other! One with 20N and the other would be 60N of force what would happen? = Reaction?

Answer 26

"if to object collided each other! One with 20N and the other would be 60N of force what would happen? = Reaction? "

Force is not a quantity possessed by a body.
During the collision of the two bodies, at every instant, the force exerted by A on B is opposed to the force exerted by B on A.
If these bodies have different masses, the effect of these equal forces will be different due to F = m1a1 = -m2a2

The mosquito and the windscreen of your car feel exactly the same force when you run into one another.

In a field, producing a force on a body, the opposite force will be felt by the creator of the field (the magnet, or the coil).

All this is not valid as such in relativity where actions are not exerted instantaneously at a non zero distance. But the concepts of momentum and energy hold and replace N's 3rd law.

Answer 27

"In a field, producing a force on a body, the opposite force will be felt by the creator of the field (the magnet, or the coil)."

Ok, that explains a magnet in a non uniform field?

Let me give you a brief example: Bring an electromagnet and a magnet.

Start the electromagnet with a weak force it attracts the magnets lets say in 2 seconds(theoretically). Now make magnetic field stronger... What would happen? The magnet would be attracted in less then 2 seconds lets say in 0.5 seconds.

What happend there? Well a force was increased and thus the total output was? For some reason I feel this is totally irrelevant :P...

Same thing is applied when repelled...

Answer 28

If one force is increased the weaker force would instantly react to it... Thats the point im trying to reach! :)

@Vincent-Lyon.Fr

Answer 29

The is no 'stronger' and 'weaker' force. The are always equal.

First both forces are equally weak, then both forces are equally strong.

Answer 30

@Vincent-Lyon.Fr

I'm confused with what you're saying I really am... This whole law is confusing :S

Answer 31

How is that? There is a strong gravitational force and a weak one. There is a strong magnetic force and a weak one. Etc... Basic answer is that if a strong force acts on a weaker force the result would be= Hope you're getting my point @Vincent-Lyon.Fr