The attraction of two magnets in repulsion to a piece of metal

[Cairun]

Hi all,


I am trying to understand why the attraction between two magnets in repulsion to a piece of metal become stronger when the magnets are brought closer together than when they are further apart.  I've run some femm simulations for both when the magnets are closer and further apart and attached the results.  Does anyone understand why this is happening?  The top(long) rectangle is the metal piece, and the bottom(shorter) rectangles are the magnets (they are in repulsion with their poles on the side or left to right).


Best regards,
Alex

[Newton II]

From your figure itself it is clear that two magnets in repulsion pump sronger flux into the iron piece inducing strong opposite pole in iron piece.  So force of attraction will be more between iron piece and magnets in repulsion. But it depends on thickness or total mass of the iron piece.  If you use a very thin iron plate, i don't think that you will observe same force of attraction.

[Cairun]

From your figure itself it is clear that two magnets in repulsion pump sronger flux into the iron piece inducing strong opposite pole in iron piece.  So force of attraction will be more between iron piece and magnets in repulsion. But it depends on thickness or total mass of the iron piece.  If you use a very thin iron plate, i don't think that you will observe same force of attraction.

Newton II,


Thanks for replying.  I agree with you on that...  But, when I rotated the poles of the magnets 90 degrees (now the poles are on top and bottom), the opposite happens.  the attraction is now stronger when the magnets are apart.  Please see attached.  As for using thin plates, you are right on that as well, the attraction decreases dramatically.  I used a 0.005 inch thick metal piece, and the attraction force fell to about 2 newtons for open magnets, and about 3 newtons for closed magnets.