This is a great playful way to visualize gravity:
http://orglr.com/t/science/612/gravity-visualized
Dan Burns explains his space-time warping demo at a PTSOS workshop at Los Gatos High School, on March 10, 2012.
Dan Burns explains his space-time warping demo at a PTSOS workshop at Los Gatos High School, on March 10, 2012.