Calculate Force Between Neodymium Magnets

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Discussion Overview

The discussion centers around calculating the force between two neodymium magnets, exploring various factors such as shape, size, orientation, and distance. Participants share their insights and experiences related to the complexities involved in determining the magnetic force between these magnets.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • Some participants propose that the force calculation must consider the shape of the magnets, as different configurations (e.g., cube vs. square) affect the force required to separate them.
  • One participant mentions that the force will depend on the shapes, sizes, and strengths of the magnets, as well as their relative position and orientation, referencing Maxwell's equations as relevant but complex.
  • A participant provides a specific example of cylindrical magnets with given dimensions and suggests a general equation for calculating force based on distance, although this is later challenged.
  • Another participant argues that the magnetic force is not exponential with distance but follows a dipole-dipole interaction model, which decreases with the cube of the distance (1/r³).
  • There is a question about the assumptions made regarding the magnets being stationary, indicating a potential variable in the calculations.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the force-distance relationship, with some supporting an exponential model and others advocating for a dipole-dipole interaction model. The discussion remains unresolved regarding the best approach to calculate the force between neodymium magnets.

Contextual Notes

Participants highlight the importance of considering various factors such as magnet shape, orientation, and distance in force calculations, indicating that the problem is more complex than a straightforward equation might suggest.

eddybob123
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hi, I was wondering if there is an equation out there that let's you calculate the force between two neodymium magnet. thanks, i would really appreciate an answer.
 
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eddybob123 said:
hi, I was wondering if there is an equation out there that let's you calculate the force between two neodymium magnet. thanks, i would really appreciate an answer.
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:
eddybob123 said:
hi, I was wondering if there is an equation out there that let's you calculate the force between two neodymium magnet. thanks, i would really appreciate an answer.

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.
 
Let's just say that the magnets are cylindrical and the face is 2 cm in diameter, and the height is 5 cm.
 
eddybob123 said:
Let's just say that the magnets are cylindrical and the face is 2 cm in diameter, and the height is 5 cm.

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
 
But assume the magnets are stationary?
 
Low-Q said:
The magnetic force is generally exponential to distance.

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

BBB
 
How do you get those number?
 

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