From: saify@cbnewsl.cb.att.com (saify.lanewala)
Subject: Re: pick before swinging
Organization: AT&T Bell Laboratories
Distribution: na
Date: Mon, 17 Aug 1992 14:25:52 GMT
Summary: Quite right -- also need backspin

In article <5a7cfffb5.003ba43@licorice.engin.umich.edu>, sudhama@engin.umich.edu (Sudhama Gopalan) writes:
> Vaibhav writes:
> Just curious, Why would picking the seam allow the bowler to swing the ball
> more?  I rememeber Chris Pringle from NZ claiming 7/30 odd and bowling
> out Pak for 102 on NZ's last tour of Pak.  He later claimed that this is
> what Waqar did thru the series and that he (Pringle) was trying to make
> a point.  In any case, I am not really interested in whether Waqar et al.
> pick at the seam or not, I just want to know if there is any explanation
> for why this would cause the ball to swing more, since I've alway associated
> swing with shine.
> 
>                                 - Vaibhav.
> ---------------------------------------------------------------------
>     I remember my first fluid mechanics class in which the swinging of a
> cricket ball and the reason why a golf ball is dimpled were cited as everyday
> examples of fluid mech in action. Here is my understanding of how an old ball
> swings. Assuiming that one side alone is kept well polished it would experience
> less friction moving through the air and hence the swing. I remember when Imran
> bowled those massive inswingers against India in '82, he never did so till he 
> came in for his second spell - that was typically after 10-12 overs had been
> bowled with the ball. Now I'd assume that grounds in India are hard enough
> and outfields rough enough to permit quick wear of the new ball - I'd probably
> want to scratch a ball in England if I was a whiz at swinging the old ball.
>   However the new ball too swings. I have a twopenny worth speculation for 
> this. I believe this is due to the presence of the seam - which disrupts the
> flow streamlines around the perfectly spherical ball - the swing then being 
> caused by the eddies/circulation at the point of disruption. The only catch in
> my little theory here is that unlike in the abovementioned case I wouldn't be
> able to figure out which way the ball would go - I'd guess that if the seam is
> pointed from off to leg the ball would be an outswinger - I frankly don't 
> know if that's the way it works in reality. Anyway the point is that bigger
> the seam more the swing - hence I'd love to pick the seam. I think picking the
> seam is criminal but removing the shine off one side of the ball is not - my
> justification  --- in the good old days when Indian pacemen were pansies and 
> the spinners were men; it was quite common to have a spinner on in the 5th over
> (say) and the first thing the spinner would do is GET THE SHINE OFF THE BALL BY
> RUBBING IT ON THE GROUND - simply for grip. If they can do it, why should a fast
> bowler be penalized for it--- well, I do concede he gains an unfair advantage
> from it; but it's not as drastic as picking the seam.
>   Or is my speculation really worth two pennies  [ :-) ]
> 
> Sudhama



Quite right.  However, I think the off-leg orientation causes the ball
to swing into the bat from the off-side, while a leg-off orinetation
causes it to swing from the leg to the off side.

Another point to note is that you must impart a backspin to the ball in
order to provide some seam stability, i.e., you want to maintain the
seam orientation all the way to the ground.

The seam orientation is most useful when the ball is new and the shine
on the ball is even on both sides of the seam.  As the ball wears, it
is more effective to simply polish the ball on one side.  In that case,
the seam orientation is not as useful, since you could counter the
fluid flow effect you are trying to achieve.

I remember, unfortunately from my days at college about twenty years ago
now, reading a magazine (some Brit fluid mechanics journal) where the
physics of swing bowling were described.  Would be nice if there was a
more recent article on that.

Saify Lanewala
UNIX System Labs., Inc.

stl@usl.usl.com