Work Work is defined as force multiplied by the distance over which the force acts. Work is measured in foot-pounds. Since very few humans can lift 300 pounds directly, a device must be employed to modify the required effort into something manageable. If the ramp were 10 feet long and friction forces were negligibly small, then 75 pounds of force would be required to roll the refrigerator up the ramp. A device that decreases the necessary applied force while increasing the distance over which the smaller force acts is called a force multiplier.
Machines can also multiply speed and distance.
A broom is an example of a speed and distance multiplier because it converts input force and distance at the handle into a lower force and larger distance at the sweeping end. Since the larger distance at the sweeping end is covered in the same time as the input distance, then the speed is also increased. In addition to modifying forces and distances, machines can also change the direction of motion. Efficiency and Mechanical Advantage Efficiency and mechanical advantage are used to gauge the performance of mechanical machines. Efficiency is defined as the useful mechanical output work, expressed as a percentage of the input work.