Thursday, August 31, 2006

Swinging in confusion

Here’s a much-awaited treatise on that great mystery of cricket – swing. While Saad Shafqat mentions a few interesting facts there about the past of swing bowling and touches upon the scientific simplicity of it all, he yorks me with the lines:

It is often said that reverse (super) swing is poorly understood, but in fact it is a simple and straightforward technique that you can try in your own backyard. All you need is a tennis ball, a roll of electrical insulation tape, and a set of stumps to aim at. Cover one half of the ball with strips of tape and hold it down the center, with the taped side entirely to one side. For a toe-bruising yorker, keep the taped side towards leg and deliver the ball aiming for second slip. About two-thirds of the way the ball will curve like a banana and crash into the base of middle and leg. The faster you are the better, but you don't have to be very quick to create the effect. To bowl a menacing outswinger, keep the taped side facing off and aim for fine leg. The physics is elementary. The smooth, taped side creates less turbulence than the uncovered, rough side of the tennis ball. Less turbulence means lesser resistance, and the ball moves in that direction.

A scientific confusion is created here. For all the elementary science lessons at your memory’s disposal and without treading into ‘turbulence’ territory you would have thought that the smoother or shiny half of the ball would face lesser air resistance and try to travel FASTER through the air than the other (rough) half and thus force the ball to move away from it, which would be the opposite of Shafqat’s take in the last two lines. The resultant trajectory, when viewed from above should resemble a heated bimetallic strip. I believe most of us laymen generally regard the normal (or conventional) swing to function that way rather than ‘reverse’ (or ‘super’ or whatever) swing.

Is the turbulence effect, that obviously functions inversely as the ‘expected’ effect explained above (let’s call it that), so strong that it overcomes this expected effect and reverses it to a degree that it becomes too negligible to even deserve a mention from Shafqat? And does the cricket ball behave in exactly the same fashion as the tape ball? In case you think of dismissing the above words of Shafqat as a typo there’s further confirmation of what he intends to say:

Super swing is simpler to understand, easier to learn, more accurate, and perfectly reproducible. Delivered at speeds over 90 mph, it can be a lethal weapon, some would even say a weapon of mass destruction. It doesn't matter what your action is or how you cock your wrist. All that matters is which way the smoother surface is facing. Provided there is enough difference between the rough and shiny sides, the ball will always move towards the smoother surface. It isn't the 'reverse' of anything. That's just the way it is.
Towards the smoother surface’ again? Now my confusion is peaking and needs serious sorting out. Having surfed on this topic a few times earlier I repeat the exercise. All of the more simplistic explanations (links provided below) that I pick up on the net point towards my original beliefs (to use a suitable term) about swing. However I’m far from convinced that I understand the truth.

Not for nothing is aerodynamics excluded from science syllabi for fifth standard students and there should be a lot more to the mechanism of swing than simplistic explanations. Simply put, the ball behaves as it does and it is up to us to find out how it moves. There’s no use expecting it to do this or that just because our expectations soar only as far as our knowledge allow them to.

Maybe ‘turbulence’ does weird and big things to the quickly hurled cricket ball and Shafqat’s statement may be based on that. How I wish this scientific misery of cricket lovers to end once for all through extensive studies on this front by a handful of crazy cricket lovers pretending as brilliant scientists.

Oh – I must kick myself hard for forgetting to thank Shafqat profusely. Controversies have deluged cricket over the last month and it is a long time since we all discussed ball, bat and such things that are easier to relate to. At least Shafqat has started a debate that we would love to shout ourselves hoarse about. Would love to read a more detailed account by him about those words of his.

Do add your views here and help enlighten me if you have understood Saad Shafqat's point. In case you wondered, I regard myself to be an on-the-verge-of-retirement non-pro medium pacer who generally swings the ball right up. And as Shafqat mentions in his post, I agree with Imran Khan that it would swing the same (almost) all the time irrespective of the way the ball is held.
More stuff on swing bowling mechanism has been discussed here, here and here.
[cross posted on Caught Behind and Different Strokes]
Update [7-Sep-2006]:

Rabindra Mehta has come up with an illustrative piece on cricinfo to explain the science of swing bowling in simple terms. My DS friend Krishna Kumar has this to say about the issue:

I know you can get conventional swing with a taped ball, if you strip away a bit of the tape on one side, after covering the whole ball first with tape, i.e. away from the shiny, smooth side and toward the damaged tape side. We used to do that for fun in Ottawa, until very quickly the batting team asked for a re-tape :)
Ball does travel faster over the turbulent air stream side. The smooth side allows air to stick to it better, roughly speaking, and hence air flow is slower. It's the same reason a dimpled golf ball travels quicker through air.
There's a ball available on order, from the Greg Chappell cricket centre online, called King Swinger or something like that (I have it with me:), it's half regular tennis ball, half smooth rubber, it swings conventionally, but swings a LOT. Very difficult to control unless you bowl as quick you can, otherwise it starts bending half way down the pitch. :)
A taped ball I'd have thought would behave much the same way, i.e. generate conventional swing, but Saad seems to suggest otherwise.
The only real difference in reverse swing and the conventional variety, is that when one side becomes really rough, air flow becomes very turbulent, and when it is really turbulent (as opposed to mildly turbulent for conventional swing), air flow slows down, resulting in a reversal of swing direction. Or so people claim :)
The real reason (I think) wrist position becomes very crucial in conventional swing, is that, the difference in air flow speeds is because of the seam position as opposed to the difference in roughness between sides of the ball. After all, the first few overs of a game, there is no rough side :) Hence, the angle at which the protruding seam cuts through the air determines the speed of air flow over and around it. That's not a very good explanation, but that's about as well as I understand it anyway :) A bit of wobble (not too much, but just a bit) of the seam I think helps (although TV comms and coaches say, you need a pefectly positioned seam), because if you notice, Zaheer Khan has about the best positioned non-wobbly seam ever, but gets almost no swing with a red ball. Or perhaps, it is the non-slinginess of his action.
But, overall, it's the vaguest science known to mankind (superstring theory being a distant second:)
God bless both.

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