This Demonstration simulates a liquid mirror. As a reflective liquid rotates, it pushes up against the walls of its cylindrical container and assumes the shape of a paraboloid. Incoming light rays parallel to the axis bounce off the liquid and intersect at a common focal point.
This Demonstration is based on a 2001 International Physics Olympiad problem . More information on the practical uses of liquid mirrors can be found on Wikipedia .
 2001 International Physics Olympiad. "Experimental Competitiion." (Jul 30, 2013) www.jyu.fi/ipho/2001/IPhO2001-EXP.pdf.
 Wikipedia. "Liquid Mirror Telescope." (Jul 30, 2013) en.wikipedia.org/wiki/Liquid_mirror_telescope.