Chapter 14
Section 3
Simple Machines
There are 6 basic types of simple
machines.

1.
2.
3.
4.
5.
6.
The inclined plane
The wedge
The screw
The lever
The wheel and axle
The pulley
Inclined Plane

Inclined plane is a flat, sloped
surface.
1.
2.
It allows you to exert your input force
over a longer distance.
Mechanical Advantage = Length of incline
Height of incline
Wedge

1.
2.
A wedge is a device that is thick at one end and tapers to a
thin edge at the other end.
When you use a wedge, instead of moving an object along
the inclined plane, you move the inclined plane itself.
Mechanical Advantage=Length of wedge
width of wedge
Screws

A screw can be thought of as an inclined plane wrapped around a
cylinder.
1.
The threads of a screw act like an inclined plane to increase the
distance over which you exert the input force.
2.
The closer together the threads of a screw are, the greater the
mechanical advantage.
1.
Think of the length around the threads as the length of the
inclined plane.
Levers

A lever is a rigid bar that is free to pivot, or rotate,
on a fixed point (fulcrum).
1. Think about opening a paint can. Pg. 426.
2. Mechanical Advantage = Distance from fulcrum
to input force ÷ distance from fulcrum to output
force.
Classes of Levers
1.
First-Class Levers – always change the
direction of the input force. Ex. Scissors,
pliers, seesaws.
1.
Second-Class Levers – increase force, but
do not change direction of the input force.
Ex. Doors, nutcrackers, bottle openers.

Third-Class Levers – increase distance, but
do not change the direction of the input
force. Ex. Fishing poles, shovels, baseball
bats
Wheel and Axle

A wheel and axle is made of two circular or
cylindrical objects fastened together that rotate
about a common axis.
 The larger radius is the wheel
 The smaller radius is the axle
 Ex. Screwdriver, doorknob, steering wheel.
Wheel and Axle


How It Works pg. 428
Mechanical Advantage = Radius of wheel
Radius of axle
Pulley

A pulley is made of a grooved wheel
with a rope or cable wrapped around it.
1. decreases the amount of input
force needed and changes direction of
input force. Ex. flagpoles
Types of Pulleys
1.
Fixed Pulley – does not change
amount of force. Only changes the
direction of force.
1.
Movable Pulley – increases output
force. Does not change direction.
Block and Tackle – made up of both a
fixed and moveable pulley.
SEE PAGE 431
1.
Compound Machines

A machine that utilizes two or more
simple machines.