Low-Power High-Force Electromagnet
To show that a small amount of energy can produce large magnetic forces.◙
Battery operated magnet with keeper.
After two of the strongest guys in the class can't separate the magnet, separate it yourself (after discreetly◙disconnecting the battery), suggesting that they are really wimps.◙
A magnet and keeper are held together by energizing the magnet with a flashlight battery. It usually takes more than one person pulling on each side to separate the magnet and keeper. ◙