Buckingham Pi Dimensional Analysis - simplifying problems by eliminating units

**Alternate title: "How to make Pi" A tutorial on the Buckingham Pi method, why dimensionless parameters are awesome (not just the Reynolds number), and how they can be used to narrow down the solution space before even a single experiment is performed. Submitted to #SoME3 ______________________________ References and images https://commons.wikimedia.org/w/index.php?curid=51841073 http://www.jpl.nasa.gov/pictures/solar/mcoartist.html, https://commons.wikimedia.org/w/index.php?curid=390903 https://www.nasa.gov/centers/ames/orgs/aeronautics/windtunnels/multimedia/truss-braced-wing, https://commons.wikimedia.org/w/index.php?curid=75848528 https://www.nasa.gov/centers/ames/images/content/109854main_AC84-0712-15.1.jpg Egdar Buckingham, https://commons.wikimedia.org/w/index.php?curid=11303643 Lord Rayleigh, https://commons.wikimedia.org/w/index.php?curid=405463 Joseph Bertrand, http://scienceworld.wolfram.com/biography/Bertrand.html, https://commons.wikimedia.org/w/index.php?curid=2818814 Vortex street animation by Cesareo de La Rosa Siqueira - http://www.mcef.ep.usp.br/staff/jmeneg/cesareo/vort2.gif, Attribution, https://commons.wikimedia.org/w/index.php?curid=87351 Pierre-Gilles de Gennes during a lecture in 2006. CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=5880337 SmarterEveryDay: https://www.youtube.com/watch?v=y7Hyc3MRKno Veritasium: https://www.youtube.com/watch?v=5zI9sG3pjVU