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 energy  A 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.

Machines  Machines do not decrease the amount of work.  Instead they decrease the force needed or change the direction of the force.  As the force decreases, the distance YOU must move the machine increases.  Simple Machines: Less force, more distance

How does this simple machine change the forces needed to get the bike on the truck?

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

9.2 Mechanical advantage  Machines 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 = F o F i Output force (N) Input force (N) mechanical advantage