The Equivalence Principle, starring Professor Mike Merrifield from the University of Nottingham (plus Albert Einstein and Isaac Newton). Feather in vacuum: http://youtu.be/cjSvxWpbP_o Visit our website at http://www.sixtysymbols.com/ We're on Facebook at http://www.facebook.com/sixtysymbols And Twitter at http://twitter.com/#!/periodicvideos This project features scientists from The University of Nottingham http://bit.ly/NottsPhysics Sixty Symbols videos by Brady Haran A run-down of Brady's channels: http://bit.ly/bradychannels