All the facts were found on this site http://www.worldbookonline.com/wb/Article?id=ar211680&st=friction
Pictures are from:
http://www.moe.gov.sg/edumall/tl/digital_resources/physics/images/friction_rolling_ball.jpg
http://doernenburg.alien.de/arch/bau/grafik/perpet.JPG
http://www.sea.edu/images/k12/Image45.gif
http://www.school-for-champions.com/science/images/friction_uses-bear.jpg
