Jumping Discs - Set of 3

These little metal discs are bimetallic - they are made from two different metals - and this enables them to perform an amazing physics trick! The disc is slightly curved, and if you heat the disc in your hands you can then 'pop' the disk so that it bends the other way. You then place it on a flat surface, and it starts to cool. As it cools, the disc will, sooner or later, revert to the initial configuration. When this happens, the disc jumps several feet in the air! Make sure your hands are not too cold - one customer reported problems in getting the discs to work. However he then realised that he had just come in from helping his son make a snowman in the garden, and his hands were really cold. Once his hands warmed up, the discs worked again! One customer suggested holding the discs against a mug of hot tea, which certainly warms them up very effectively! These discs were originally supplied by Edmund Scientific in New Jersey some 15-20 years ago. When the man in charge of the operation sadly passed away, nobody knew how to produce the discs anymore. Now a new designer in Europe has started making them again.

HOW DO THEY WORK?

The discs are in interesting example of differential expansion. The disc is a bimetal, having stainless steel on one side and invar on the other. Invar is a nickel-iron alloy containing 36% nickel. This alloy has a very low coefficient of linear expansion by comparison with the stainless steel. Heat causes the bimetal disc to expand and cooling makes it contract. Since the two surfaces expand and contract at highly different rates in response to changes in temperature, it is possible to 'lock' the disc in the loaded position when it is hot; then, as the disc cools, the increasing tension will eventually cause it to jump into the air as it reverts to its original shape!

The discs are 25.4 mm in diameter. 

Supplied as a set of 3 discs. Made in EU