Strong Nuclear Force

You can't see an atom, so you can't see how its protons clump together to make the nucleus. But you can see a similar effect when the force of magnetism (a kind of electricity) works against the force of gravity. All you need is a magnet and a paper clip, a piece of thread and some tape.

Tie the string to the paper clip and tape the other end of the string to the table. Hold the paper clip up so that the string is extended straight up. Hold the magnet over the top of the paper clip, just far enough away so that they don't touch.

The thread pulls the paper clip down, and magnetism pulls the paper clip up. So the paper clip hangs in the air, just the way protons hang around the nucleus of an atom, although in an atom it is magnetism that pushes the protons away from each other, and the strong nuclear force that pulls the protons in, towards each other.

(You can use this method to make a little puppet show: cut out people from tissue paper and tape them on to paper clips. Use string and tape to fasten these paper clips to the table. Put a block in front of the strings so people can't see them. Now you can make your people move back and forth by moving magnets held above them.)