Middle School Physical Science: Work and Machines - Machines — Flashcards

A machine is any device that makes work easier by changing a force. When you use a machine, you apply force to the machine. This force is called the input force. The machine, in turn, applies force to an object. This force is called the output force. The force you apply to a machine is applied over a certain distance, called the input distance. The force applied by the machine to the object is also applied over a certain distance, called the output distance.    
Machines make work easier by increasing the amount of force that is applied, increasing the distance over which the force is applied, or changing the direction in which the force is applied. Contrary to popular belief, machines do not increase the amount of work that is done. They just change how the work is done.

The work done on a machine or by a machine always equals force multiplied by distance. Because a machine doesn't change the amount of work that is done, a machine that increases force must apply the force over a shorter distance. For the same reason, a machine that increases the distance over which the force is applied must apply less force.