falling objects research

http://www.grc.nasa.gov/WWW/K-12/airplane/ffall.html
http://www.grc.nasa.gov/WWW/K-12/airplane/mofall.html
http://hyperphysics.phy-astr.gsu.edu/hbase/flobj.html
http://www.swiftless.com/tutorials/opengl/collision.html
http://www.mvps.org/directx/articles/using_bounding_spheres.htm