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The Science of Swing Bowling

Physics | 7-14 yrs

Interschool Premier League (IPL)

It was a hot sunny day, but the heat didn’t stop the excitement at school. For Eeshan cheering for his friends from the stands was a joyful experience. With the Indian Premier League around the corner, the school had organized an interschool premier league, an IPL of their own.

The school they were competing with, had a bowler, Rubin, known for taking quick wickets and restricting the other team to a total that most often lead to their defeat. Eeshan’s school was going quite strong with players like Martin and Nitin, but their dream run was showing signs of halting. Nitin was bowled out by Rubin’s first ball and the ground went mute. Eeshan ran up to his friend while Nitin was walking back to the team, to check on him.

“Don’t worry Nitin. We have Martin at the crease,” assured Eeshan.

“Yes, thank God for that! But don’t understand how the ball swung. It was quite unreal. Either he is a really good bowler or the ball is magical,” said Nitin.

Eeshan’s investigative bent of mind went on an overdrive. He had noticed Rubin’s bowling technique with Nitin and Martin at other matches. For Eeshan the matches were just an opportunity to laugh at the excessive hair gel that Rubin had on his hair, while Martin and Nitin studied their opponents so they could beat them in a match. Oddly Rubin used to keep running his hand over his hair before bowling every ball to the batsman. During the match he also noticed Rubin scuffs the seam of the cricket ball.

“Why does he keep doing that?” Eeshan said to himself loudly, not noticing Nitin was still beside him.

“Why does he do what?” asked Nitin, still upset about losing his wicket. He could see Martin struggling with Rubin as well.

“You remember the chapter on Aerodynamics Nitin?” Eeshan asked.

Nitin said, “Not now Eeshan! Let’s just talk about the match and be supportive here.”

“No, wait! I might know how Rubin is able to get his opponents out so easily. He is cheating!” said Eeshan.

“Cheating? How?” Nitin was now interested to know about Eeshan’s find.

“Well Mr. Murthy taught us aerodynamics the other day and you remember he told us about how this topic can help us play better cricket too?” asked Eeshan.

“I missed that class. I was taking trials for the tournament with the coach,” Nitin answered.

“Oh yes! Let me tell you how he applied aerodynamics to explain swing bowling. When a ball leaves the bowler’s hand a thin layer of air forms a boundary around the surface of the ball. The boundary air can’t stay around the surface of the ball for long and tends to separate at some point. The point where the layer separates determines the pressure on the ball and a slow separation creates lower pressure on that side. A swing is only generated if there is a pressure difference between the two sides of the ball which comes with a minimum speed known as the critical speed.”

“You know the seam of a cricket ball divides it into two sides, the smooth side and the rough side. As the ball gets older this difference between the two sides is more prominent and the critical speed becomes lower. But a new ball can be tampered so that the difference is prominent. For example, by rubbing lubricants like gel, lip balm, etc. on one side to make it smoother or scuffing the ball to make it rougher. This is called ball tampering and it produces a great swing that helps bowlers a great deal.”

Nitin said, “Is that why Rubin wears so much hair gel?”

Eeshan said, “Possibly! We must report it to the match referee and take Mr. Murthy with us. This is against the rules of the game.”

They immediately went to Mr. Murthy and then the match referee and told them what was going on. After the neutral referee observed closely what was happening, he declared that Rubin and his team had been using illegal means to win matches. Their school was, therefore, disqualified.

At the celebratory dinner, Eeshan and his friends were sitting with the coach.

“Good riddance. Just shows that any game should be played in the spirit of it. Good catch Eeshan, even though you are not in the team you played your part well,” the coach said.

“He had to, Sir. Eeshan is our 12th man,” said Martin and everyone had a hearty laugh.

Looking for more physics articles and videos? Go to: Physics for Kids.

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