This document discusses how machines make work easier by changing the amount of force needed, the distance over which force is applied, or the direction of the applied force. It defines simple machines, mechanical advantage, efficiency, and ideal machines. Specifically, it explains that machines reduce the needed force but may increase the distance of application. The mechanical advantage is the output force divided by the input force. Efficiency compares the work output to work input as a percentage, with higher percentages indicating less energy loss and more efficient machines. An ideal machine would lose no energy to friction.

2. Machines April 15, 2009

4. History of Work

5. Simple Machines