Magnetic Force: Halving the Distance

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SUMMARY

Halving the distance between two magnetic poles significantly increases the force of attraction or repulsion. The force can quadruple when the distance is halved, particularly for small button or disk magnets where the magnetic field strength decreases as 1/r^3 when poles are close together. For bar magnets with poles farther apart, the force follows a 1/r^2 relationship. Additionally, permanent magnets can temporarily increase their strength in an external magnetic field, demonstrating complex interactions based on distance and saturation levels.

PREREQUISITES
  • Understanding of magnetic field strength and behavior
  • Familiarity with the concepts of attraction and repulsion in magnetism
  • Knowledge of the mathematical relationships governing magnetic forces
  • Basic principles of physics modeling
NEXT STEPS
  • Research the mathematical modeling of magnetic forces, focusing on 1/r^2 and 1/r^3 relationships
  • Explore the effects of saturation in permanent magnets and their behavior in external magnetic fields
  • Study the differences in magnetic field strength between various types of magnets, such as disk and bar magnets
  • Investigate experimental setups to measure magnetic force variations with distance
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Physics students, educators, engineers, and anyone interested in the principles of magnetism and magnetic force interactions.

mystry4
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Am I correct in assuming that if the distance between two poles of different magnets is halved, then the force of repulsion (or attraction) will increase while the attraction (or repulsion) will decrease? If the distance is halved, isn't the force quadrupled?
Thanks.
 
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Magnetic Field strength decreases far from the source.

If the source magnet has poles "close" to one another
compared to width (ie, small button or disk magnets),
then the field drops off roughly as 1/r^3 (not 1/r^2).

If the poles are very far apart compared to their width,
(5"x1" bar magnets have poles only about 3" apart)
then their field drops off roughly as 1/r^2 .

A little button magnet in a uniform B-field will
experience almost zero (intrinsic) net Force,
but in a spreading field will experience net Force
proportional to the the distance between poles.

Permanent Magnets (the ones filled with metal)
respond in subtle ways to being in a B-field ...
becoming temporarily stronger than usual,
with extra strength proportional to external B.

So, with small non-saturated disk magnets,
you could get F ~ 1/r^6, (7 in special cases)
but with "well-isolated" magnetic poles that
are almost saturated, F could go as 1/r^2 !

Physics is about *modelling* Nature,
whatever the behavior is that we observe.
 

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