# Magnetic Force of identical shaped box bar magnets

## Main Question or Discussion Point

I am having a problem with my understanding. I could be incorrect, but I think that the magnetic field emitted from a magnet is consistent and doesn't weaken at points further away. Then could someone explain how magnet force weakens with distance. I would also like to know the math so here is a problem I created.

Say I have two identical shaped box bar magnets with dimensions (l,w,d) and mass m, and magnetic field b/

The face of w*d is the side that is directed at each magnet. (ie wxd of magnet_a faces w*d of magnet_b)

Variable x is the distance between the two magnets.

So, how can I figure the forces at x.

Sorry, I accidently put this in wrong forum

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Take a refrigerator magnet and hold it 10 meters from a refrigerator. Is there much force? That should tell you something qualitative about the force vs. distance.

There is no such thing as a "bar magnet with magnetic field b" so the second part has no answer.

@Vanadium you are no help. I didn't say if magnets force get weaker I said how does it.

Also then, why are magnets rated in Teslas. Such as Neodymium which is 1.2-1.6 Tesla at poles.

Staff Emeritus
2019 Award
@Vanadium you are no help. I didn't say if magnets force get weaker I said how does it.
I think that the magnetic field emitted from a magnet is consistent and doesn't weaken at points further away
When you make up your mind, we can talk.

Then could someone explain how magnet force weakens with distance. I would also like to know the math so here is a problem I created.
Use the Biot-Savart law (http://en.wikipedia.org/wiki/Biot_savart) or Ampere's law (http://en.wikipedia.org/wiki/Ampere_law) to express the magnetic field as fuction of distance, you will find that the magnetic field is inversely proportional to distance.

To find the magnetic force, you will then need to use the Lorentz force applied on a charged particle moving in a magnetic field (http://en.wikipedia.org/wiki/Lorentz_force).

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Bio Savart works with a moving charge, but I don't know the speed the electrons. What formulas can be used to determine the repelling or acting force of magnet. And what information do I need about a magnet's strength that will help me.

Bio Savart works with a moving charge, but I don't know the speed the electrons. What formulas can be used to determine the repelling or acting force of magnet. And what information do I need about a magnet's strength that will help me.
Wow! Your problem is now getting serious but check this out http://en.wikipedia.org/wiki/Magnetic_field

Nice one here!
That force is a gravitational one. I hope you realised the inverse square proportionality which means that the force dies as the distance between two magnets poles are far away!
Thanks dm164!