Why Do Mirrors Flip Left & Right (but not up & down)?

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Go to https://nebula.tv/minutephysics to get access to Nebula (where you can watch MinuteBody) plus you'll get a 20% discount on an annual subscription. Support MinutePhysics on Patreon! http://www.patreon.com/minutephysics Link to Patreon Supporters: http://www.minutephysics.com/supporters/ This video is about why words flip left & right (aka horizontally) in a mirror but not up & down (aka vertically). The answer has to do with specular reflection, mirrors being like windows into another world (alternate universes, just with in and out flipped!), and transparency of the things we write on. REFERENCES Specular Reflection https://en.wikipedia.org/wiki/Specular_reflection PhysicsGirl video about mirrors https://www.youtube.com/watch?v=vBpxhfBlVLU Fermat’s principle http://electron6.phys.utk.edu/optics421/modules/m1/Fermat's%20principle.htm Thomas-Fermi screening https://en.wikipedia.org/wiki/Thomas%E2%80%93Fermi_screening MinutePhysics is on twitter - @minutephysics And facebook - http://facebook.com/minutephysics And Google+ (does anyone use this any more?) - http://bit.ly/qzEwc6 Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich