Coffee Cup Stirling Engine

With the Coffee Cup Stirling Engine ($119) your morning mug of joe can energize more than your weary mind. Just this kit, and a few tools you probably already have laying around, are all you need to build your very own heat-powered engine. Give the propeller a spin and it’ll keep running for as long as the water or coffee in your cup stays hot. The secret is in the heating and cooling of the air inside the cylinder, which drives the piston. For a bonus experiment, see what happens when you place the engine over ice.