I love seeing cool science made real with clever tricks. This pendulum can be started from a standstill, but when out in the sun will start itself swinging back and forth, faster and faster, without being touched.
How does it work? A solar panel at the top sends a little bit of juice to some coils in the base. Those coils then send the magnet in the pendulum moving back and forth. As it keeps swinging, it picks up momentum. And there's even enough juice left over to power a small LED light at the top.
The whole thing is a homemade project, too, which makes it all the more awesome. Science!