# When two objects Attract/Repel(Charges/magnets/electromagnets/etc )

By Newton's 3rd Law, YES:D

magnets can apply force to a lot of things, eg. another magnet, magnetic metals, charge, etc.
and the forced are calculated in different ways.
For example:
1) Forces between two magnets: http://en.wikipedia.org/wiki/Force_between_magnets
2) Forces between a magnetic field and a charge : Lorentz force - F = qv×B

If you are using the equation for the force between two electromagnets given in the reference I supplied earlier, then this value appears to be about 16 orders of magnitude too big - you need to check the units. Note also: "Gauss" is not the unit for magnetic pole strength used in that reference.

The correct values and units for use with the equation are given in the reference.

Here is that reference again:
http://en.wikipedia.org/wiki/Electromagnet#Force_between_electromagnets

For the general case, you will be interested in:
http://en.wikipedia.org/wiki/Force_between_magnets

Ampère's model is really complicated... How can I figure out m1 and m2?
I can't find any references that give out examples. I can't learn this by my own it way to complicated...

I'm not sure what a magnet "moment" even is... Could any of you elaborate?

Most cases of the magnetic moment is relevant to a current carrying loop...
Its helpful interms of the a electromagnet, but what about a manget?

Simon Bridge
Homework Helper
The first link is not working.
Im guessing its a link to "electromagnets" in wikipedia? I'm reading it.
The first link was the one you got the original k.m1.m2/r^2 equation from. It works for me. But you are right - it links to the "electromagnets" page in wikipedia.

Ampère's model is really complicated... How can I figure out m1 and m2?
... Magnetism is complicated, yes. Sorry.
You figure out the magnetic pole strengths for electromagnets by following the definition - the first link gives you an equation.
Note: did you try using the Gilbert Model?
I can't find any references that give out examples. I can't learn this by my own it way to complicated...
Trawl the college electromagnetism courses. This is not normally taught before second year.

I'm not sure what a magnet "moment" even is... Could any of you elaborate?
Did you look it up?

Most cases of the magnetic moment is relevant to a current carrying loop...
Its helpful in terms of the a electromagnet, but what about a magnet?
You can model any magnet with a magnetic dipole .. that's why you have "north" and "south" poles.
The Gilbert model is more useful for permanent magnets - but it can depend on what you plan to do with it.

Have you looked to see what other people did?

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I studied a college level lecture that deal's with the relation of magnetic field and a electric field and relativity mathematically.

But when solving F of a pole. (N/S) For example: S is attracted to the N pole, I'd have to figure out the pole strength of S in Ampere*m^2 and divided it by r. So , F = (k) M1/r^2
The good news for me is, that knowing the force that magnet's pole experiences is dependent on that magnet's pole as M1. That was very informative.
F = (k) M1M2/ r^2 shows me that the total force between the two magnets is caused DUE to BOTH poles. Meaning the two poles are responsible for the force.

Ampere's model is to hard to figure out... Gilbert's model is very useful to give me a general idea but bad to relie for correct values.

I'm not sure about magnetic moments, but all I know is that it's the force a that a magnet(dipole) can exert and experience from another magnetic field(Please correct me if I'm wrong I feel that I'm off track!).

I'll try to get used to the magnetic dipole models... It tough but I'll try.
I'll most likely use F = k m1m2 / r^2, with permanent magnets interactions and electromagnets because it just gives me the idea of what's going on, and is most commonly used in examples...

Also studying Magnetic potential energy. A question though, The higher the magnetic moment the greater the field thus the greater the MPE? The energy is low when the poles are aliened the energy is high when the poles are not aliened.

Please do share you're ideas about what I've said, and if I said anything wrong... Do correct me with a brief explanation... I've been studying this for a while.

If only I can figure out an easy way to know the "pole strength" of each pole that would make my life easier!
Simon could you tell me how would you figure out such a thing? What methods would you use?
Or could you site me an exact reference?

BTW, is the K = 8.99x10^9 ?

Simon Bridge
Homework Helper
you (post #57 above) said:
BTW, is the K = 8.99x10^9 ?
me (post #49) said:
you (post #48) said:
K = 8.99x10^9
If you are using the equation for the force between two electromagnets given in the reference I supplied earlier, then this value appears to be about 16 orders of magnitude too big - you need to check the units. Note also: "Gauss" is not the unit for magnetic pole strength used in that reference.
...
The correct values and units for use with the equation are given in the reference.

You have read the reference (you: post #52), but you did not see the correct value??

Are you having trouble reading or understanding the references?
Will you be better served reviewing core skills?

Well I assumed it is. While reading I didn't fine it no.
Still, how can I figure out the magnitudes of each pole in Ampere*m^2?

Well, the reference give out a lot of information but, I didn't find the explanation of how to measure the pole strength for example?

I'd just want to know the answer to that question first before moving one or going back, because right now I'm stuck!

But how about my understanding of the magnetic moment and magnetic potential energy.
Is it correct?