Sunday, April 27, 2014

On the Boundary Lynn Catch

I am not big on following the Indian Premier League (IPL), but have noticed this fantastic match winning catch that Chris Lynn took to get AB DeVilliers out. If you have not seen it yet here it is on the StarSports website. [If you are in America - here is the YouTube link]

This catch is one of the most athletic ones we have seen in cricket and also he seems to pull off a physics defying jump where he catches the ball and still manages to land within the boundary line. There are certain stills of the catch (like the one above) that would convince you that he had to fall over the line and divine intervention or a extra strong draft of wind is the only thing that made him land well within the boundary limits. This obviously prompted this question on Quora - "Why didn't Chris Lynn fall on the boundary rope while making the best catch in cricketing history?" Here's my answer -

Let's start with a slight detour - There is a very famous (& I think very cool) physics fact about pole vault. When a pole vaulter jumps a high bar, her Center of Gravity (CG) need not go as high as the bar she needs to clear. In other words, at the top of the jump the pole vaulter needs to go over the bar and not her CG. To achieve this the pole vaulter arches her back forwards or backwards to be in a situation where the body is clear of the bar but the CG passes under for the most optimal jump. The idea being that Newton's laws only dictate the trajectories of the CG and not the entire body.

Lynn's miraculous falling back within the boundary rope is something similar. After the little stumble he has just before he makes his jump, he has his eyes on the ball. Accesses the trajectory of the ball and it looks something like this -

Now Lynn considers jumping straight up and try get the ball. Is there a chance he can make it? His jumping ability is limited and there is only a limit to which he can raise his CG. He would not have caught the ball.

However, if he jumped and turned back at the same time things could look very different even if the his jumping ability is considered to be the same. As this diagram illustrates -

At this point if a snap was taken it seems as if he would fall on the boundary rope, but he has some angular (spin) momentum on his side which a still would not capture.

He does exactly that makes the catch and after which since his CG is still very much inside the boundary region he can easily use his flexible and agile body to bring his hands inside the boundary rope. Eventually using his hands to safely land well within the boundary.

I am sure Lynn did not go through all this physics in his mind before making the catch, but intuition is a powerful physics engine due to the world experience it has.


  1. Cricket was always a physical game .. With thsi catch its,surely come a physicsal sport

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