NASA
Nasa: Beginner's Guide to Aerodynamics
This site from NASA provides a graphic depicting Newton's second law. Graphic is accompanied by an explanation. Part of a larger site with additional information on Newton's laws.
Science and Mathematics Initiative for Learning Enhancement (SMILE)
Smile: Momentum Conserved
This site by the Illinois Institute of Technology gives a Lab activity in which young scholars use a variety of toys to discover Newton's second law and momentum conservation. Newton's cradle, skate boards, and a toy motorcycle are...