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I am looking make a quick and dirty test ring using an off the shelf electromagnet. My force needs are small, less than a pound but I need to do so in a non contact manner. I know these magnets are strong but I was looking for a back of envelope formula to estimate holding force at various distances. I am thinking 1cm away from the surface of magnet. The hope is to get a 100+ lbs holding force magnets and still have a 1 or 2 lbs of hold a bit of distance away from the surface.

Thanks in advance.

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You will have to solve this by experimentation. There is not a simple equation for the reduction of magnetic force as an object is moved away from a magnet.

The reason for this is that a magnetic field isn't a simple sphere. First imagine all the field lines that leave north side of the magnet and loop around to the south side. These lines actually form a circuit, a magnetic circuit. Like an electrical circuit, the field lines will follow the most conductive pathways, for magnetism that would be pieces of iron and such. Unlike with electricity, even empty space will conduct a magnetic field to some extent.

Pieces of iron or other permeable material can shunt a magnetic field around some areas, or concentrate it in others. This makes for a field that is difficult to model with a simple algebra equation.

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