How to calculate the force between magnets?

  • Context: Undergrad 
  • Thread starter Thread starter ZecronTech
  • Start date Start date
  • Tags Tags
    Force Magnets
Click For Summary

Discussion Overview

The discussion revolves around calculating the force between magnets, particularly focusing on the conditions under which one magnet can hover above another. Participants explore the implications of magnetic field strength, the geometry of the magnets, and the mathematical approaches to determine the forces involved.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant presents a scenario involving two magnets with a field strength of 1.5 Tesla and questions the height required for the top magnet to hover while supporting a weight of 1 Newton.
  • Another participant reiterates the formula for magnetic force between poles, suggesting that it is valid only if the poles are treated as points.
  • A participant questions the significance of the shape of the magnets, specifically whether the difference between point poles and circular areas affects the calculations, and seeks guidance on how to approach this problem.
  • There is a suggestion to integrate differential forces between differential areas on each magnet, with one participant expressing uncertainty about the feasibility of this approach.
  • A later reply introduces the concept of using the Maxwell stress tensor to calculate the total force on the object, referencing external material for further understanding.

Areas of Agreement / Disagreement

Participants express various approaches to calculating the force between magnets, with no consensus on the best method or the significance of different geometries. The discussion remains unresolved regarding the integration of forces and the applicability of different models.

Contextual Notes

Participants acknowledge limitations in their mathematical understanding and the complexity of integrating forces over non-point geometries. There is also a lack of clarity on how to apply the Maxwell stress tensor in this context.

ZecronTech
Messages
6
Reaction score
0
For example at the surface of both magnets, the field strength is 1.5Tesla. Suppose the top magnet plus the weight it's supporting is 1 Newton, what is the height that I need to separate both magnets of like facing poles so that the top magnet hovers?
 
Physics news on Phys.org
ZecronTech said:
For example at the surface of both magnets, the field strength is 1.5Tesla. Suppose the top magnet plus the weight it's supporting is 1 Newton, what is the height that I need to separate both magnets of like facing poles so that the top magnet hovers?

Hint: The magnetic field B by a given pole of a bar magnet at a point (assume unit north pole) r cm away from its centre is given by,

B= (μoqm/4π(r-l)2)

Where qm is the pole strength of bar magnet. l is the "half length" of the bar magnet.

Hence classically the force between two poles of bar magnet is defined by F = Bqm. This formula is valid if the poles are mere points.
 
Last edited:
  • Like
Likes   Reactions: 1 person
sankalpmittal said:
Hence classically the force between two poles of bar magnet is defined by F = Bqm. This formula is valid if the poles are mere points.

So what if the poles aren't points like in the example that I gave. Suppose the magnets facing each other are circular. Would the difference between points and a circle area of 3cm2 be significant? If so, then how would you calculate it? (Forgive me if this post was already answered. I used the search function and came up with nothing related to this situation).
 
What about intregrating the differential forces between differential areas on each magnet? Would it work? Do you know what I mean?
 
ThomasO said:
What about intregrating the differential forces between differential areas on each magnet? Would it work? Do you know what I mean?

Yup I was also thinking the same, although I don't know how to do it. It's a bit above my math level.
 

Similar threads

Undergrad Is this analogy between Magnetic Force and Gravitational Force accurate in helping to understand what contributes more to a stronger magnetic force?
  • · Replies 11 ·
Replies
11
Views
2K
Undergrad Questions related to magnetic shielding separating two like poles
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad How induction works within a coil (nuances of it)
  • · Replies 6 ·
Replies
6
Views
2K
High School Magnetic fields attracting two disc-shaped magnets
  • · Replies 11 ·
Replies
11
Views
3K
Undergrad Can nested solenoids trap particles?
  • · Replies 12 ·
Replies
12
Views
1K
Undergrad The difference between calculating energy from 1 vs. 2 magnets?
  • · Replies 3 ·
Replies
3
Views
1K
Undergrad Motional EMF in Faraday disc, co-rotating magnet axial mean flux
  • · Replies 5 ·
Replies
5
Views
1K
Undergrad Charge movement relative to magnetic field frame dependence/invariance
  • · Replies 5 ·
Replies
5
Views
2K
Undergrad Force between opposing magnets
  • · Replies 7 ·
Replies
7
Views
2K
Undergrad Question about Activating Solenoids that are facing each other
  • · Replies 1 ·
Replies
1
Views
2K