en.wikipedia.org/wiki/Lever
atlantis.coe.uh.edu/archive/science/science_lessons/.../lever.htm
www.brainpop.com/technology/simplemachines/lever/
www.google.com
atlantis.coe.uh.edu/archive/science/science_lessons/.../lever.htm
www.brainpop.com/technology/simplemachines/lever/
www.google.com