© Getty Images

What is a bowling machine, and how does it work?
A bowling machine is a device that functions as a nets bowler, firing balls at batsmen, providing them with practice. The machine can simulate various types of pace, swing, and spin bowling accurately.

The main mechanism in a mechanical bowling machine (the most common kind) consists of two spinning wheels, each driven by its own motor, between which the balls are fed via a chute. The device is mounted on a tripod or similar, at such a height as to simulate the delivery of a bowler of average height. The machine runs on rechargeable batteries; each charge provides between two and six hours of running time.

How are swing and spin imparted?
Swing is produced by varying the speeds of the wheels independently using a manual controller - i.e., speeding one wheel up and slowing the other one down, which produces an effect similar to that caused when a football is kicked with the outer part of the foot. The ball swerves away from the faster wheel.

To impart spin, in addition to having the wheels move at different speeds, the machine head is tilted and then swing rotation is put on the ball. The ball turns because the rotation is at an angle when it hits the ground.

The length of deliveries can be adjusted by tilting the head of the machine as required.

What are the fastest and slowest speeds one can get?
The speed can be varied from 20mph to 95mph.

What sort of balls are used in these machines?
The bowling machine is most accurate with a round object, and cricket balls are not perfectly round. Moreover, cricket balls are made of leather, which is prone to tearing when squeezed between the spinning wheels. This is why hard polyurethane balls - dimpled for swing - are used.

What other kinds of bowling machine are there?
An advance over the mechanical version is the programmable bowling machine, which can be configured to bowl different types of deliveries in sequence. A programmable bowling machine called Merlyn, which it was claimed could bowl any ball known to man, including Shane Warne's legbreaks, was in the news when it was used by England in the run-up to their successful 2005 Ashes campaign.

More common are pneumatic bowling machines, which use a pump to provide a flow of air that propels the ball through a tube at varying speeds.