# Calculate magnet repulsive force?

I'm looking to make a "floating" model by insetting NdFeB rare-earth magnets with same poles facing so they repel. Now, magnet selling places specify the "pull" a magnet might have, say 1.2kg. What I would like to know is if the repel is equal in magnitude as the pull if two similar magnets are placed with same poles facing, is the force exerted 1.2kg and so I could float 1.2kg of stuff? Also, does stacking magnets double the attractive or repelling force, i.e. do two 1.2kg magnets stuck together lift 2.4kg of stuff, negating the small difference in distance of one magnet from the object? Is there a way to calculate the distance between two opposing magnets with a force applied. Does it follow the inverse cube rule? And if the stacking does work, do I also need an equal number of magnets on the other side for repelling, i.e. a stack of two 1.2kg magnets repels 2.4kg with one 1.2kg on the other side, or not? Does the magnet on the other side have to be the same force? Lots of questions but hoping someone can shed some light on this as I've not been able to find anything about it :-(

## Discussions

To answer your first question no the repletion is stronger than the pull try taking to magnets and put the same poles together they push apart you will eventually get tired

. http://en.wikipedia.org/wiki/Magnet#Units_and_calculations_in_magnetism

It is very difficult to accurately predict forces between magnets. Stacking magnets does increase the flux density but not in a linear fashion. Don't forget that a magnetic field is a three dimensional beast. Stacking magnets changes the shape of the field as well as the flux density within the field. Most often magnet strength is quoted with a -0- air gap. If a neodymium is quoted as 10000 G (e.g. gauss = 1 T or tesla) that is at the surface. Move away from the surface of the magnet and the force falls off quickly according to orientation and distance.

Specifically, you'd want to use this equation (assuming use of cylindrical magnets)

http://en.wikipedia.org/wiki/Magnet#Force_between_two_cylindrical_magnets

One must be careful using these equations because there are so many different unit-dimensions being used (i.e. teslas, gauss, newtons, coulombs, etc.) as well as multi-dimensional constants. If you mix up an SI with a CGS you will get erroneous results.