-- Physics of a Playground -- http://www.fmalive.com/_downloads/playground_physics.pdf
 
--Seesaw Physics -- http://www.tennessee-teea.org/See%20Saw%20Physics%20Lesson.pdf  

-- Swing -- http://en.wikipedia.org/wiki/Swing_%28seat%29   

-- Physics on the Playground-- http://www.schooltube.com/video/9f6450b5c54a2c0bc9fa/Physics-on-the-Playground 

--Playground Physics-- apps.caes.uga.edu/sbof/main/lessonPlan/PlaygroundPhysics.pdf  

--Centripetal force-- http://en.wikipedia.org/wiki/Centripetal_force