Childrens Illustrated Encyclopedia

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568

SometimeS the SimpleSt inventionS are the most important.

Although no one is sure exactly who invented the first wheel, the earliest

records go back to about 5,500 years ago. the wheel has made possible a

whole range of machines, from photocopiers to jet engines, that we take

for granted today. Wheels have a unique characteristic—they are circular,

without corners, enabling them to roll or spin evenly. this allows almost

all forms of land transportation—bicycles, cars, trains, and trams—to roll

smoothly along roads, rails, and rough ground. in addition, the circular

motion of a wheel means that it can transmit power continuously from an

engine. many more inventions are based on wheels. the crane, for example,

relies on pulleys (grooved wheels

around which a rope is passed), which

reduce the effort needed to lift heavy

weights; gears multiply or reduce the

speed and force of a wheel and are

essential in countless other machines.

GeArS

Sets of interlocking toothed wheels

are called gears. Gears transfer

movement in machines and

change the speed and force of

wheels. For example, a large gear

wheel makes a small gear wheel

rotate faster, but the faster moving

wheel produces less force. Gears can also

change the direction of the motion.

inventinG the Wheel

the first recorded use of a wheel dates

back to around 3500 bce. this was the

potter’s wheel, a simple turntable used in

Southwest Asia by mesopotamian pottery

workers to make smooth, round clay pots.

About 300 years later, the mesopotamians

fitted wheels to a cart, and

the age of wheeled

transportation

began.

Wheels held together

by wire spokes appeared in

about 1800. They are very light and

strong and were first used for cars,

bicycles, and early airplanes.

In the 1950s metal wheels

replaced wire wheels on cars.

About 4,500 years ago, the Ancient

Egyptians built great triangular pyramids

as tombs and temples. Gangs of workers

dragged huge blocks of stone with the

aid of log rollers.

Bibendum, the

famous symbol

of the French tire

company Michelin

Axle And beArinGS

A wheel spins on a shaft called

an axle. Wheels often have ball

bearings—several small steel balls

that run between the axle and the

wheel, allowing it to turn smoothly.

Without bearings, the great weight

of a Ferris wheel (above) would

squeeze the wheel against the axle

and prevent it from turning.

The first vehicle wheels used for carts were

solid wood. They were made of two or three

planks of wood fixed together and cut into a

circle. They first appeared in about 3200 bce.

Wheels with spokes

developed in about 2000 bce.

Spoked wheels are lighter

and faster than solid

wheels and were

fitted to war chariots.

Wheels

Tires

Car and bicycle wheels have rubber tires

filled with air. they give a comfortable ride

and all, except those of racecars, have a tread

(a pattern of ridges) to help them grip the road.

Scottish engineer robert W. thomson

invented the first air-filled tire

in 1845.

GyroSCopeS

A gyroscope is a rotating

wheel mounted on a frame.

When the wheel spins, its

momentum makes it balance

like a spinning top. once

a gyroscope is spinning, it always

tries to point in the same direction.

Aircraft, ships, and missiles use

gyroscopes to navigate, or direct

themselves, to their destinations.

The gear wheels are connected

by teeth that interlock (fit

exactly) into each other. Their

mutual positions decide how

the force changes.

Find out more

Cars

plastics

transportation, history of

Before wheels were invented,

people had to push or drag

heavy loads over the ground.

Perhaps watching a smooth

rock roll down a hill gave

people the idea of using

wheels for transportation.

US_568_Wheels.indd 568 09/02/16 5:29 pm