Ask Me Everything7

What’s so great about wheels?

Wheels are really simple objects—just disks or hoops with a hole in the middle for an axle—

but we’d find it difficult to live without them. They are not just used on cars, bikes, and other vehicles —many machines have wheels inside.

r

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Yariations on wheels

Pulley

A pulley is a wheel with a groove around the edge into which a ropę or cable fits.

Gears

A gear is a wheel with teeth around its edge. The teeth of two gears tum each other around.

Flywheel

A flywheel is a heavy wheel that Stores energy when it spins.

Who invented the wheel?

• No one knows who invented the wheel.

• Cartwheels were used in an ancient land called Mesopotamia (modern-day Iraq) around 5,500 years ago.

• The idea for the first cartwheel might have come from the potter’s wheel. This was a spinning wooden table used for making clay pots. It was in use for perhaps one thousand years before someone thought of turning it into a cartwheel.

Spokes are rods or wires that connect a wheel's hub, in the middle, to its rim.

Most

-TŁ    bicycles

^have

f \ wheels with wire

9    spokes.

Some racing bicycles have solid wheels with k no spokes.

Traditional horse-drawn carriages have wheels with wooden spokes.

The worlcTs fastest car wheels help jet-powered cars set speed recorcls. These wheels are madę of solid metal because they spin so fast that rubber tires would fly apart.

Wacky wheels

Unicycle: One wheel with a seat on top. It’s morę difficult to balance on one wheel than two.

Uno motorbike:

Looks like half a bike, as if it has only one wheel. It actually has two, but they are side by side instead of one in front of the other!

Segway: A

two-wheeled electric vehicle that balances by itself. The rider stands on a platform between the wheels.

Leaning forward speeds it up,

^    leaning back

W    slows it down.    A

Leaning to one side makes    km

it tum.    Wm

Tires through the ages

01: The first tires were madę of iron around 2,800 years ago. They were ńtted around wooden wheels to stop them from wearing down so quickly.

02: The first cars and bicycles had solid rubber tires.

03: Pneumatic (air-filled) tires began replacing solid tires on cars and bicycles in the 1890s.

(c) 2011 Dorling Kindersley. Ali Rights Reserved