How to find a ruler's centre of gravity. More videos with Tadashi Tokieda: bit.ly/tadashi_vids Sixty Symbols (our physics channel): www.youtube.com/sixtysymbols NUMBERPHILE Website: www.numberphile.com/ Numberphile on Facebook: www.facebook.com/numberphile Numberphile tweets: twitter.com/numberphile Subscribe: bit.ly/Numberphile_Sub Numberphile is supported by the Mathematical Sciences Research Institute (MSRI): bit.ly/MSRINumberphile Videos by Brady Haran Additional editing an animation for this video: Pete McPartlan Support us on Patreon: www.patreon.com/numberphile Brady's videos subreddit: www.reddit.com/r/BradyHaran/ Brady's latest videos across all channels: www.bradyharanblog.com/ Sign up for (occasional) emails: eepurl.com/YdjL9 A NOTE ON THIS VIDEO: A few of our Tadashi videos blur the already blurry line between mathematics and physics... Some people suggest they may be a better fit on Brady's dedicated physics channel (called Sixty Symbols). In response, the reasons they are on Numberphile are: 1) Tadashi, while certainly a modern polymath, is based in a mathematics department. 2) This sub series (with its animation and extra production work) has been supported by the Mathematical Sciences Research Institute, a Numberphile collaborator. 3) Some of the previous and future Tadashi videos are more math-oriented than physics - and it just makes sense to put them on one channel rather than dividing the series between two channels on an ad hoc basis. In a multi-disciplinary world, it is challenging to run YouTube channels which people come to associate with just one discipline. That said, feel free to go over and watch hundreds of physics videos on Sixty Symbols --- www.youtube.com/sixtysymbols