Credit: CK-12 Foundation - Samantha Bacic, using images copyright Denniro, 2013 and yusufdemirci, 2013
License: CC BY-NC 3.0
If you push against a wall with all your strength for a full minute, how much work have you done? You might think you've worked very hard, but from a physics definition you haven't completed any work. Completing work from a physics point of view requires not only force, but also movement of an object.
Imagine trying to lift a 400 lb object, such as the blue box shown above. Could you do that by yourself? If you simply leaned over and tried to pick it up, you'd never be able to. However, a series of pulleys such as the system shown above allows a single person to lift a 400 lb object without any other assistance.
This chapter examines the physics definition of work, the relationship between work, force, and power, and the mechanical assistance provided by simple machines.
Work, measured in Joules, is the measurement of the force exerted on an object in the direction it moves multiplied by the distance the object moved. Power, measured in Joules/second, is the amount of work done divided by the time it took. Machines are devices that transform input work into equivalent amounts of output work in a different form; a small force over a large distance may become a large force over a small distance. The six simple machines discussed in this chapter are the building blocks of all machines.