Chapter 11 Section 4

Simple Machines

What is a Simple Machine? Is a machine that

takes one force and changes its direction, distance, or strength.

A simple machine has few or no moving parts.

Simple machines make work easier.

Introduction

Simple MachinesEffort – force you apply to a machine

Output- the force a machine supplies

Load- the object moved

Simple machines can increase the force we apply.

Simple MachinesWork = force x distanceSimple machines make work easier

because it can increase force needed to move objects or they can decrease the amount of force needed to move the object.

Examples of simple machines are levers, pulleys, wedges, wheel & axle, inclined planes, and screws.

What are Levers ? A lever is a bar that rests on a support

called a fulcrum which lifts or moves loads .

Fulcrum- the pivot point for a lever

Levers multiply effort, distance, and speed.

Levers-First Class In a first class lever

the fulcrum is in the middle and the load and effort is on either side.

The effort and out move in opposite directions.

Think of a see-saw

Levers-Second Class In a second class

lever the fulcrum is at the end, with the load and effort on one side.

Think of a wheelbarrow

Effort ^

Levers-Third Class In a third class lever

the fulcrum is again at the end, but the effort is in the middle

Think of a pair of chop sticks

Wheels and Axles The wheel and axle

are a simple machine.

The axle is a rod that goes through the wheel which allows the wheel to turn to lift or move loads.

Gears are a form of wheels and axles

Pulleys Pulleys are wheels

and axles with a groove around the outside used to raise or lower a load.

A pulley needs a rope, chain or belt around the groove to make it do work.

Inclined Planes An inclined plane is

a slanting surface connecting a lower level to a higher level.

Inclined planes make the work of moving things easier.

Wedges Two inclined

planes joined back to back.

Wedges are used to split things.

Wedges are also used to lift objects.

Screws A screw is an inclined

plane wrapped around a pole which holds things together or lifts materials.

The inclined plane

allows the screw to move itself when rotated.

Compound Machines Compound machines- two or more

simple machines used to move a load.

A compound machine can also use the same simple machine multiple times.

Efficiency- ratio of input energy to output work.

Compound Machine Bulldozer – lever and wedge

Wheelbarrow- levers, wheel and axle,

Scissors- levers and wedges

Hand drill- screw and wheel and axle

Elevator- multiple pulleys