The Ninja Star

The Ninja Star is actually called a Hamilton's mill but in physics it's called a Electrostatic pinwheel. The reason it gets spinning is because the spinner is positively charged, like the dome. Each point has a strong electric field around it. Air molecules close to the points lose electrons and become positively charged ions - their electrons were attracted to the points and used to neutralise some of the charge on the dome. Positively charged ions are repelled by the positive star's points and move away. The points move in the opposite direction (Newton's 3rd law) so the star Spins.