12,000 years ago there was an impressive (for its time) dynamics demonstrator named "xspringies", (which is still listed on the rutgers site: http://www.cs.rutgers.edu/~decarlo/software.html ) it would let one build mobile or anchored objects with selected internal spring constants which would respond to various parameterized imposed forces. by now someone must've written something that would far transcend xspringies. i'll assume that this falling ball demo is more sophisticated and responsive in various ways along those lines.