Quick! Get up and twirl around as fast as you can for three straight minutes, then jump as high as you can into the air! Feel that free-falling, vertigo sensation? If not, why not go on a rotor ride? Designed in the 1940s by engineer Ernst Hoffmeister, the Rotor has many versions in theme parks all over the world. The premise is pretty much a simple lesson in centrifugal force: Take a large barrel and revolve the walls of said barrel really fast. When it's going super fast, drop the bottom out of the barrel, and watch as all the people inside stick to the walls. Other names for this simple but popular ride include Gravitron and Vortex.