How would you find the magnetic force on a piece of metal by an electromagnet?

AI Thread Summary
The discussion focuses on calculating the magnetic force exerted by an electromagnet on a piece of metal, emphasizing the importance of the metal's magnetic properties in the calculations. It highlights that the force of attraction is proportional to the square of the magnetic field strength at the electromagnet's contact point, with one Tesla producing a pull force of 58 pounds per square inch. Factors such as air gaps, including paint or rust, significantly affect field strength and should be considered in calculations. Participants also mention using tools like FEMM for practical calculations. Understanding the geometry and assumptions about the substrate is crucial for accurate force estimations.
breadandbacon
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Does the metal being attracted make a difference?
How would you find the force on the metal knowing the field strength there?
How would you even calculate the field strength of an electromagnet with a core? In my case, it is one of those junkyard electromagnets.
thanks
 
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When you grab something with an electromagnet, you are making a magnetic circuit. To learn how to calculate, search magnetic circuit. The magnetic properties of the metal being attracted are part of the calculation. Keep in mind that the field strength is strongly affected by any air gaps, and that a layer of paint or rust is an air gap.

The force of attraction is proportional to the square of the field strength at the face of the electromagnet where it contacts the metal. A field strength of one Tesla has a pull force of 58 pounds per square inch of pole area.
 
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jrmichler said:
The force of attraction is proportional to the square of the field strength at the face of the electromagnet where it contacts the metal. A field strength of one Tesla has a pull force of 58 pounds per square inch of pole area.
A useful number...there must be some assumption about the rest of the geometry, though? I am guessing this is for a "long" magnet with flat pole on a semi-infinite substrate??Any assumptions about substrate (obviously ferromagnetic I guess) but does it somehow not matter?I would find this a very useful thing to know but don't understand when to apply it. Thanks
 
yall i ended up just using FEMM and it worked out fine
 
Thread 'Motional EMF in Faraday disc, co-rotating magnet axial mean flux'

Thread 'Motional EMF in Faraday disc, co-rotating magnet axial mean flux'

So here is the motional EMF formula. Now I understand the standard Faraday paradox that an axis symmetric field source (like a speaker motor ring magnet) has a magnetic field that is frame invariant under rotation around axis of symmetry. The field is static whether you rotate the magnet or not. So far so good. What puzzles me is this , there is a term average magnetic flux or "azimuthal mean" , this term describes the average magnetic field through the area swept by the rotating Faraday...
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