Magnetic star

You can create amazing constructions out of those colourful sticks. But you always have to place a metal ball between them. If you don't, the whole thing will fall apart.

Now think carefully: magnet either repel each other or attract each other. If one end of the stick attracts another stick, the other end of the first stick should repel the second stick. And it would be so if we didn't place the metal ball between the poles.

The metal ball (made from so called 'soft', easily magnetized, metal) 'fits itself' to the poles. If it is close to three poles of the same sign(e.g. N), the ball induces three opposite poles in their directions (S). Because magnets always have two poles, three N-poles are generated somewhere in the middle of the S-poles on the surface of the ball.

If you don't believe it, check it using the board of the magnetic sketcher.