Page 75 - How It Works - Book Of Amazing Answers To Curious Questions, Volume 05-15

Science

What are the physics

of the cricket ball?

In a game of fine margins, physics can make

all the difference The mystery of
reverse swing
he movement of a cricket ball is unique revolutions on the ball to allow it to spin

within the sporting world. When the ball fiercely once it has pitched. Slow spin works Reverse swing, where the ball swings in
Tis delivered, a layer of air known as a better on dry and dusty pitches where the ball the opposite direction to the conventional
‘boundary layer’ forms over the ball. This is can skip off the pitch. way, is a rare delivery that can dismiss
where the physics come into play. By angling Side forces also act on the ball in swing even the most experienced batsmen. Made
the seam – the stitched part in the middle – the bowling. When one side of the ball becomes famous by the likes of Wasim Akram and
bowler can alter the pressure of the forces on rougher than the other, that half becomes less Imran Khan, the cricket ball can become
almost unplayable. Readily achievable at
the ball and choose which way the delivery streamlined. Bowlers frequently use this to bowling speeds of over 135 kilometres (84
will go. The aerodynamics can be varied their advantage to move the ball sideways in miles) per hour, reverse swing works best
further by the bowler changing the pace of the the air in order to confuse batsmen into when the ball is old and rough. Now the
ball and where the ball bounces. These playing false and poorly timed shots. The effect ball is not shiny so it will move in the
deliveries are known as ‘cutters’ to cricket fans of swing can be exaggerated even further by opposite way to what is expected from a
and the practice is called seam bowling. Spin is shining one side of the ball, although using conventional swing. The boundary layer is
another weapon in the bowler’s armoury. Spin anything other than your cricket whites to affected quicker, allowing an in-swinging
bowlers use their wrist or fingers to put rough the ball up is considered unsporting. bowler to bowl out-swinging deliveries and

vice-versa. As the bowler doesn’t change
his grip, there is no hint to the batsman
Cricket physics that the ball will move the other way. It is
said that overcast and humid weather can
From the moment it is released, strong aid swing bowling, but further research
forces work upon the little red sphere into this remains inconclusive. If a bowler
masters reverse swing, the odds will be in
his favour.
Boundary layer
Movement through the air This thin layer of air James Anderson is
When the ball is airborne, the stitched seam surrounds the ball as England’s premier
and the smooth and rough sides create air it travels through the swing bowler, making
the ball reverse swing
pockets that make it move unpredictably. air. This is when the at high speeds
forces begin to act
Grip upon the ball.
The bowler’s grip can Rough side
determine how spin, swing The rough skin makes Seam position
and seam act on the ball the airfl ow more The stitching is
upon delivery. turbulent on this side. essential for good
seam bowling that
Delivery stance moves off the pitch
The ideal delivery stride for a once it has bounced.
bowler is to be upright,
causing as little strain on the
back as possible.

Backspin and Smooth side Pace and bounce
slower balls In conventional Swing can be achieved by
A useful trick in the swing, the shiny some bowlers at lower
bowler’s armoury, the side allows air to speeds, but for most, it is only © Getty; Thinkstock
slower ball can fl ow smoothly possible at around and above
deceive the batsman. around it. 135km/h (84mph).

How It Works 75