# Neo magnet force

1. Oct 17, 2011

### eddybob123

hi, I was wondering if there is an equation out there that lets you calculate the force between two neodymium magnet. thanks, i would really appreciate an answer.

2. Oct 18, 2011

### Low-Q

If there is an equation, this must also consider the shape of the magnets. Two magnets with same mass and grade will have different "center of magnetism".

Say you have two cube magnets, N40, with the volume of 1cm^3. These will not get closer to the center than approx 5mm. To pull them apart require a given force.

Say you have two square magnets measuring 1mm x 31.6mm x 31.6mm (1cm^3), and you put them together surface to surface, it will require greater force to separate them. If you put them together edge to edge, it will require less force to separate them.
In addition, there will be different force required between magnetized through thickness, and through length. Surface to surface, and magnetized through length will allow the magnetic flux to have a tighter and more dense flux loop, which also require even greater force to separate.

However, at greater distance both shapes will attract practically equal for both shapes.

I have done a lot of experiments with this.

Vidar

Last edited: Oct 18, 2011
3. Oct 18, 2011

### chrisbaird

Finding the answer is more detailed than I think you are expecting. The force will depend on the shapes, sizes, and strengths of the magnets, as well as their relative position and orientation. The equations that describe the interacting fields are Maxwell's equations, but they have to be applied to a specific problem.

4. Oct 19, 2011

### eddybob123

Let's just say that the magnets are cylindrical and the face is 2 cm in diameter, and the height is 5 cm.

5. Oct 20, 2011

### Low-Q

The magnetic force is generally exponential to distance. If you know the force at 10cm distance, the force is increased 4 times at 5cm distance.

The general equation would be this: Forceinitial x (initial distance / new distance)^2
Example:
Initial distance Di is 10cm.
New distance Dn is 7cm
Initial force Fi is 2N
New force Fn is unknown

Fn = Fi(Di / Dn)^2 =
2N(10cm/7cm)^2 = 4.08N

Vidar

6. Oct 20, 2011

### eddybob123

But assume the magnets are stationary?

7. Oct 20, 2011

### bbbeard

Magnet-magnet interactions like the OP is asking about are dipole-dipole interactions and go like 1/r3, not exponential.

BBB

8. Oct 22, 2011

### eddybob123

How do you get those number?