Pull force of magnet calculated at an angle

  • Thread starter Mozez
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  • #1
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Hi PF,

A disclaimer, I am no good at Physics or math.

My question:

When calculating the pull force between two magnets it seems to always be calculated at an angle perpendicular to the surface of the magnet.

I was wondering what effect on the force required to "pull" one magnet away from the other would be when a force is applied at a different angle and can this be calculated easier when you already know the pull force at the perpendicular?

I guess Im looking for a way of recalculating the force needed to 'pull' a magnet away from another when the angle of the applied force changes.

Thank you for your time
 

Answers and Replies

  • #2
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Force_at_angle = cos (angle_from_perpendicular) * Force_at_peroendicular
 
  • #3
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Thank you for replying.

Wouldn't this imply that at 90 degrees to the perpendicular that there is no force required to pull the magnet seeing as cos(90) = 0?

Unless you mean angle_from_perpendicular in radians? But then the resulting force needed is only minutely different. Maybe this is the case? That the force difference between shearing a magnet away from another or pulling perpendicular are roughly the same? It doesn't seem to be so though.

I obviously still need a bit of guidance on this.

Thanks
 
  • #4
96
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Good point. This is because at 90 degree's the magnetic force is from a different part of the magnet.

Magnetic forces are caused by moving charges (generally electrons) in the plane perpindicular to their travel. A moving charge does not create a magnetic force perpendicular to this, i.e. in its direction of travel.

Now a magnet is like a closed electric circuit, with electrons moving round the outside. If you put the north of the magnet facing upwards the electrons are moving round it in the clockwise direction.

So lets go for a cuboid magnet for my simplicity. I'm gonna ignore the N and S end bits. But lets say its a cuboid with faces f1,f2,f3,f4 and areas a1,a2,a3,a4 and such that a1=a3 and a2=a4, i.e. these are opposite faces. Since its a cuboid all these faces will have the same height but different width.

If we know the force when perpindicular to one face (say f1, call this force F) and we want to know it when we move it around angle theta from the perpindicular. It would be:

F*cos(theta)+(a2/a1)*F*sin(theta)

Just to let you know this is just me thinking aloud, I'm always doing magnetic forces from currents or electrons, not bar magnets. A better resource might be:

http://en.wikipedia.org/wiki/Force_between_magnets#Calculating_the_magnetic_force
 
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