July 10, 2013. First day of Ashes test series between England and Australia. When slow left arm orthodox bowler Ashton Agar started bowling, a wheel popped up on the TV screen. Written on the wheel was- ‘2338 RPM’. Do you know what this means?
This was the inception of a new technology to be used in cricket, at 2013. This technology is known as ‘Ball Spin RPM’. It was used first in 2013 Ashes, courtesy of Sky Sports.
RPM abbreviates to Revolutions per Minute. Science has described RPM as, the number of times an object rotates in an axis within a minute. Ball spin RPM tells us about the rotation per minute of a spinner’s ball. That means we can know how fast the ball was rotating when the spinner threw it. Also we can know the direction of rotation.
This technology uses a High speed camera which stays focused on the ball. There’s no clear description available regarding how this technology works. It is assumed that images received from the Hawk-Eye are processed to determine the RPM. This means High speed HD cameras are used to capture different positions of the ball. These footages are compiled and a 3D rendition is created. This 3D rendition helps to tell the direction of the ball rotation.
Also, HD cameras shoot high pitch sound waves at the spinners bowling line. This wave bounces off the ball when it pitches. This reflected wave is captured and examined by the camera to tell us how much the ball rotated.
So, RPM tells us about how much the ball was rotating and which way it was rotating.