A Fairly Common Magnetic Toy

• Magnetic force
• Attractive and repulsive magnetic force
• Magnetostatic and electrostatic mapping

This fact realize a fairly common magnetic toy. This fact is widely familiar outside physics; many may even be able to come up with an explanation along the lines of: ‘like poles repel, unlike poles attract’. Sticking bar magnets onto each other (linearly) and/or using ball bearings as ‘joints’ (thus allowing a range of angles between two magnets), a whole variety of structures can be built up. What is the basic structural motif of the toy kit, namely, a bar magnet with a steel ball bearing stuck on one of its poles?

Presumably, when a second magnet is sufficiently far away, the magnet-and-bearing unit would look just like another bar magnet, so that when like poles face each other, repulsion is the result. On the other hand, the success of the toy depends on a second bar magnet actually being attracted to the bearing irrespective of the relative identities of the poles facing each other across the steel ball. This suggests that there should be a change of the interaction from repulsive to attractive as a ‘bare’ bar magnet approaches the magnet-plus-bearing head on with like poles facing each other (across the steel ball). This was indeed found to be the case.

• Plastic Cased Bar Magnets — 4611.40

• What is a magnet?
• What is happening when you cut a magnet?