 You have now seen examples of the simple machines inclined planes (including ramps, wedges, and levers) and wheel and axles.  Before we discuss pulleys as simple machines, we need to define the term "mechanical advantage."

Machines take effort or energy and use it more efficiently. Many machines help work to be done by multiplying the force of your effort. The amount that your effort has been increased is called the mechanical advantage (scientists use the symbol “MA” for short). A machine can create mechanical advantage by decreasing the amount of force needed to do work, even though the actual amount of work does not change.

Mechanical advantage is described by comparing the output force to the input force. The output force is the amount of force that the machine applies to do the work. The input force is the amount of force needed to operate the machine. To find the mechanical advantage, the force output is divided by the force input. This is what the equation looks like:

 Mechanical Advantage (MA) = force output / force input

For instance, if a machine allows you to move an 80 newton rock (a rock which is exerting 80 newtons of downward force), it has a force output of 80 newtons. If you are only exerting 20 newtons of force to operate the machine, there is a force input of 20 newtons. You could measure the advantage of using the machine by dividing 80 newtons by 20 newtons.

The mechanical advantage is shown as follows:

MA = force output / force input
MA = 80 newtons / 20 newtons
MA = 4

This means that the machine increases the force you apply by 4. The machine allows you to be four times stronger than you really are.