Google- http://www.google.com/search?site=&tbm=isch&source=hp&biw=1280&bih=684&q=wheel+and+axle&oq=wheel+and+axle&gs_l=img.3..0l10.2114.6231.0.6340.16.9.2.5.6.0.63.509.9.9.0...0.0...1ac.1.12.img.bK-9ZrH_zPA&surl=1&safe=active#imgrc=cPnB6tYmO7pdjM%3A%3BIVRS7IodD1r3_M%3Bhttp%253A%252F%252Fetc.usf.edu%252Fclipart%252F36300%252F36343%252Fwheelaxle_36343_lg.gif%3Bhttp%253A%252F%252Fetc.usf.edu%252Fclipart%252F36300%252F36343%252Fwheelaxle_36343.htm%3B783%3B1024
Wiki- http://en.wikipedia.org/wiki/Wheel_and_axle
Kirkwood- http://www.kirkwood.k12.mo.us/parent_student/te/diedril/website/force%20and%20motion/wheel.htm