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Carr, K.E. “Screws.” Quatr.US Study Guides. April 2017. Quatr.us. 1 May 2017.
http://quatr.us/physics/machines/screw.htm
Carr, K.E. “Wedges.” Quatr.US Study Guides. April 2017. Quatr.us. 1 May 2017.
http://quatr.us/physics/machines/wedge.htm
Carr, K.E. “Wheel and Axle.” Quatr.US Study Guides. May 2016. Quatr.us.
1 May 2017. http://quatr.us/physics/machines/wheel.htm
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Carr, K.E. “Levers.” Quart.US Study Guides. April 2016. Quatr.us. 1 May 2017
http://quatr.us/physics/machines/lever.htm
Carr, K.E. “Screws.” Quatr.US Study Guides. April 2017. Quatr.us. 1 May 2017.
http://quatr.us/physics/machines/screw.htm
Carr, K.E. “Wedges.” Quatr.US Study Guides. April 2017. Quatr.us. 1 May 2017.
http://quatr.us/physics/machines/wedge.htm
Carr, K.E. “Wheel and Axle.” Quatr.US Study Guides. May 2016. Quatr.us.
1 May 2017. http://quatr.us/physics/machines/wheel.htm
“Early Inventors and Inventions: the 1300’s and earlier.” EnchantedLearning.com.
2000. Enchanted Learning. 1 May 2017.
http://www.enchantedlearning.com/inventors/1300.shtml
Foresman, Scott. Science See learning in a whole new light. Glenview, Illinois: Pearson
Education, Inc., 2006.
Gundrum, Carolyn. “Simple Machine.” MIKIDS.COM. 2011. 27 April 2017.
<http://mikids.com/Smachines.htm>
“Pulley.” New World Encyclopedia. 16 June 2015. New World Encyclopedia Online.
1 May 2017. http://www.newworldencyclopedia.org/entry/Pulley