A super-fast, super-cool car that uses the pent-up energy inside a mouse trap spring to propel a homemade car forward.
While normally this is reserved for high school physics classes, it really is a fun and inexpensive experiment to do with kids of all ages.
This is a great demonstration of how energy changes form. At first, the energy was stored in the spring of the mousetrap as elastic potential energy, but after the trap is triggered, the energy is transformed into kinetic energy as rotation of the wheels.