Chapter Nine: Simple Machines

9.1 Types of Simple Machines

9.2 Mechanical Advantage

9.3 Levers in the Human Body

9.1 Using Machines

A machine is a device with moving parts that work together to accomplish a task.

A bicycle is a good example.

9.1 Using Machines The input includes everything you do to

make the machine accomplish a task, like pushing on the bicycle pedals.

The output is what the machine does for you, like going fast or climbing a steep hill.

9.1 Forces in Machines

A simple machine is an unpowered mechanical device, such as a lever.

9.1 Review of work Every process that is done by machines

can be simplified in terms of work:

1. work input: the work or energy supplied to the process (or machine).

2. work output: the work or energy that comes out of the process (or machine).

9.1 Review of energyA rope and pulley

machine illustrates a rule that is true for all processes that transform energy.

The total energy or work output can never be greater than the total energy or work input.

9.2 Mechanical advantageMechanical advantage is the ratio of output force to input force.

9.2 Mechanical advantageMachines multiply forces.

One person could lift an elephant—quite a heavy load—with a properly designed system of ropes and pulleys!

9.1 Mechanical Advantage

MA = Fo

Fi

Output force (N)

Input force (N)

mechanicaladvantage