friction
input force
output force
mechanical advantage
efficiency
Explanation of force, Newtons, and mechanical advantage of simple machines in the context of pulleys.
Source: http://www.schooltube.com/video/12874d5652424a84f591/Mechanical%20Advantage%20-%20Pulleys
Fixed and movable pulleys
Source: http://www.schooltube.com/video/8e99351c37e03e30659e/Pulleys%20-%20simple%20machines
Cartoon comparing the efficiency of inclined planes and levers in the context of friction.
Source: http://www.schooltube.com/video/e8419c70e9bdf67d3d85/Eureka!%20Episode%2013%20-%20Mechanical%20Advantage%20and%20Friction