Childrens Illustrated Encyclopedia

328

Small effort, but the

rope has to move

a large distance.

Gears

Gears are interlocking

toothed wheels. They

can increase force or

speed depending

on the relative size

of the wheels and

their number of

teeth. a gearwheel

driven by a smaller

wheel turns less quickly

than the smaller wheel

but with greater force.

a wheel driven by a larger

wheel turns faster but

with less force.

Pulleys

lifting a heavy load

is easy with a pulley

system. It contains a

set of wheels attached

to a support. a rope

goes around grooves

in the wheels. Pulling

the rope raises the

lower wheel and the

load. a pulley system

allows you to lift a

heavy load with little

effort, but you must

pull the rope a large

distance to raise

the load by a

small amount.

Pulley

Force

Load

AutomAtic mAchines

Many machines do not need to

be operated by people. These

are automatic machines.

They contain mechanisms

or computers to control

themselves. These

machines may simply

perform a set task

whenever it is required;

automatic doors, for

example, open as people

arrive. Other machines are

able to check their own work

and change the way they

operate to follow instructions.

One example is an aircraft

autopilot, which guides the

plane through the skies.

Object moves a

small distance.

lever

a long stick propped up on a small object

(a fulcrum) helps you move a heavy load.

The stick is a simple machine called a lever.

Pushing down on the end farthest

from the fulcrum raises the

other end with greater

force, helping you move

the load. Other kinds of

levers can increase either

the force applied to, or

the distance

moved by,

a load.

There are three types of levers.

A crowbar is called a first-class

lever. The fulcrum is between

the load and the effort, which

is the force that you apply.

A wheelbarrow

is a second-class

lever. The load

lies between the

fulcrum and

the effort.

A fishing rod is

a third-class lever.

The load moves

a greater distance than the effort,

but with less force. The effort pushes

between the load and the fulcrum.

Wheel

and axle

several machines use the

principle of the wheel and

axle. One example is

the winch, in which

a handle (the wheel)

turns a shaft (the

axle) that raises

a load. The handle

moves a greater

distance than the

load rises. The winch

therefore lifts the load

with a greater force than

the effort needed to turn

the handle.

sTeerInG Wheel

The steering wheel on a car is an example

of the wheel and axle. The shaft turns with

greater force than the effort needed to

turn the steering wheel.

A pair of scissors

consists of two levers

hinged together.

Mechanical clocks and watches

contain gears that turn the hands

at different speeds.

Fulcrum

Effort

Effort

Load

Force

Fulcrum

Load Effort

Force

Force

Find out more

Computers

engines

Industrial revolution

robots

Technology

machines

Fulcrum

Load

Fulcrum

Effort

Force

Effort

Traffic lights are machines that

control traffic automatically.

Load

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