Magnets

Magnets are really cool and fun to mess around with. Eventually, you'll break a few magnets. At that point, you'll definitely realize that magnets can can't be easily fixed once broken in two. At that point, you just have two magnets. They will repel each other from certain angles and stick to each other from others.

Basically each magnet possesses a north pole and a south pole. Once broken in two, both magnet parts still require an individual north pole and south pole. The north pole of the first magnet piece will be attracted towards the south pole of the second magnet piece. Poles of the same type will reject each other.