The magnets are quite brittle. Don't let them fall on to hard surfaces (like concrete) from a height – they may shatter into sharp pieces. Straight copper pipe, at least 30cm long. 15 or 22mm ...

the magnets create a rapidly flipping magnetic field. To test this setup, [Tim] used a scrap of copper pipe with a bit of water inside. Holding it over the magnets as they whiz by rapidly heats ...

They are often used for making jewellery, like crowns. Most other metals are not magnetic. Copper pipes that carry water around your house and aluminium foil in your kitchen are not attracted to ...