The animation above came from:


http://www.physicsclassroom.com/mmedia/estatics/itsn.html

http://www.physicsclassroom.com/mmedia/estatics/isop.html

http://www.physicsclassroom.com/mmedia/estatics/esn.html

http://www.physicsclassroom.com/mmedia/estatics/gep.html

http://www.physicsclassroom.com/mmedia/estatics/gen.html