This is an intriguing little device. Looks pretty small and simple, doesn't it?

It's small but it's not simple. This coiled piece of wire violates the following rules about how things behave in the normal world.

When you overstretch a spring you've spoiled it. It can't be fixed in any reasonable way.
When you cool off a piece of metal it contracts.
When you heat up a piece of metal it expands
Thermally induced changes in a piece of metal of uniform material are too small to see with the naked eye.

Great gift for the student of any age. Smart kids love this, because they know it's something new and different. If you have a smart child or grandchild they will be fascinated!.