Calculating Magnetic Force Between Two Magnets

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Discussion Overview

The discussion centers around calculating the magnetic force of attraction between two magnets, specifically when they are in contact and at varying distances apart. Participants explore the complexities involved in determining this force and seek a straightforward equation or method for practical applications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant inquires about a simple equation to calculate the force required to separate two magnets and the pull strength at a distance.
  • Another participant notes the difficulty in specifying the strength of permanent magnets due to the presence of multiple magnetic poles and suggests that calculating the force is easier for electromagnets or parallel wires.
  • A participant expresses that the available information is too advanced and reiterates the need for a calculation method for a specific application.
  • It is mentioned that there is no simple way to calculate the force, and that manufacturers often rely on measurements rather than theoretical calculations.
  • Links to external resources are provided, including a calculator page that estimates pull forces based on product testing rather than theoretical assumptions.
  • One participant shares a formula involving variables such as contact surface area and magnetic induction, asking for clarification on the symbols used.
  • Another participant provides definitions for the symbols in the formula, noting that it assumes magnetic induction is constant in the gap between magnets.

Areas of Agreement / Disagreement

Participants generally agree that calculating the magnetic force between permanent magnets is complex and lacks a straightforward solution. Multiple views on the applicability of different methods and the challenges involved remain present throughout the discussion.

Contextual Notes

Limitations include the dependence on specific conditions such as the assumption of constant magnetic induction and the variability of real-world measurements compared to theoretical calculations.

Seaningtime
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I've been searching for a simple answer online and on this site, but I haven't been able to find anything that explains this for me.

Simply, is there an equation that can be used to calculate the force of attraction between two magnets?
I am interested in when two magnets are touching, how much force will be required to separate them?
And when they are x distance apart, how much pull strength will they exhibit?

Thank you
Sean
 
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Hi and welcome to PF.
You haven't been able to find anything much about this because the 'strength' of real permanent magnets is hard to specify. The problem is that you are dealing with (even ideally) four magnetic poles, an N and a S on each one. At a large distance, they can be characterised by their Dipole Moment (whatever shape they are) and the force is easier to calculate but, when you are interested in the useful strength (for actually making use of them) it is much harder.
It is much easier to discus the Magnetic Force between two electromagnets - even easier to calculate the force between two parallel wires, carrying current.
Have you looked at the Wikipedia article? Does it have enough information for you?
Is your interest a general one or do you have a specific application and are you wondering what to buy?
 
I did take a look at that wikipedia article, but it is pretty advanced for me...
I do have a specific application that I am looking to use this for and, really, I need to figure out what I first mentioned, I figure there must be some way to calculate it...?
 
There is no simple way. It's possible to calculate the force that a relay coil applies to the contacts (eg to work out the return spring force required) but I bet relay manufacturers only use that as a starting point and do measurements to confirm.

http://info.ee.surrey.ac.uk/Workshop/advice/coils/force.html#nfringe

Perhaps see "Pull Force Case 3 Magnet to Magnet" on this calculator page...

https://www.kjmagnetics.com/calculator.asp

Note:

Most online calculators determine pull force based on a theoretical calculation of the flux density. With a few assumptions, flux density (in Gauss) can be related to the expected pull force. Unfortunately, this simplification often fails to match experimentally measured data. This page calculates expected pull forces based on extensive product testing.
 
Seaningtime said:
I've been searching for a simple answer online and on this site, but I haven't been able to find anything that explains this for me.

Simply, is there an equation that can be used to calculate the force of attraction between two magnets?
I am interested in when two magnets are touching, how much force will be required to separate them?
If the magnets are of same area A then:
gif.latex?F%3D\frac{B^{2}}{2\mu%20_{0}}\cdot%20A.gif
 
Thanks guys for all the responses!
zoki85- that looks like the formula that I'm looking for, what do the symbols represent?
 
A- contact surface area between two nearly touching magnets
B- magnetic induction in a very short gap between attracting magnets
μ0- permeability of free space

The formula assumes B is constant in the gap
 
thank you
 

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