Robert Penner created a suite of mathematically genius actionscript functions to simulate real-life movements in Flash. The results are compelling.
A few years back, I ported Robert Penner's equations to JavaScript for use with Scriptaculous transitions. Here is a little playground I set up to test them out. They are available for download there as well. Here is Rober Penner's original demo and Easing Equations page.
We see swinging, bouncing, and elastic movements in real life, and even a lot on Flash and even TV due to the work of Rober Penner.
Thomas Fuchs uses my custom bouncePast transition on his site!