He was predominantly an inswing bowler at the time and so the "wrong way" meant that the ball would swing away from the batsman. At the time, I honestly did not believe that such a phenomenon could occur since I could not explain it scientifically.
However, in the following year, when we conducted our wind-tunnel experiments, the whole "mystery" was revealed. The flow over a ball exhibiting reverse swing is shown in Fig 3.
So now, at a high enough bowling speed over about 85mph for a new ball the laminar boundary layer transitions into a turbulent state relatively early, more importantly before reaching the seam location. In this case, the seam actually has a detrimental effect on the turbulent boundary layer by making it thicker and weaker and it therefore separates earlier than the turbulent layer over the bottom surface.
Still following this at the back of the class? That means that the asymmetry is now switched and so is the side force.
Result: the ball swings in the opposite or reversed direction. It is only true reverse swing if the ball swings in a direction that is opposed to that of the seam. This means that the fastest bowlers in the world, who bowl at over 90mph, will only produce reverse swing, even with a brand new ball. Of course, not many bowlers can bowl at 90mph, so how can us mere mortals produce reverse swing? Well, that is where the surface roughness comes into play.
As the roughness on this leading side facing the batsman is increased, the critical bowling speed above which reverse swing can be obtained is reduced experimental data showing this effect can be found in a New Scientist magazine article, Vol , No.
It also means that more effective reverse swing will be obtained at the higher bowling speeds. This is why reverse swing generally comes into play with older balls. The whole beauty of reverse swing is that a bowler who could only bowl outswingers at the onset with the new ball can bowl inswingers with an older ball without any change in the grip or bowling action.
Similarly, an inswing bowler will suddenly be able to bowl outswingers. For a classic exposition of reverse swing, check out the third Test of the Ashes - Andrew Flintoff to Simon Katich in the second innings. One of the reasons why reverse swing has gained such notoriety is its constant link to accusations of ball-tampering, as we witnessed at The Oval in Once bowlers realised the importance of the rough surface, they started to help the process along.
They showed me several balls that had been confiscated after the umpires suspected the fielding side of ball-tampering. From what I saw, the most popular forms of tampering consisted of gouging the surface using foreign objects such as bottle tops and attempting to open up the quarter seam using fingernails.
Perhaps what is not that well-known is the fact that positive roughness can work just as well. So if some dirt was stuck to the ball's surface using sweat or saliva as the glue , reverse swing could be obtained at nominal bowling speeds on even a brand new ball, and best of all, the evidence is gone by the time the ball reaches the wicketkeeper.
Is that what Atherton was attempting? I doubt it, but I wonder if other players ever tried it, especially in the days when sawdust was routinely used to dry a wet ball. The one misconception about reverse swing that is commonly heard even today is that it occurs due to a weight imbalance created by wetting one side of the ball.
This is based on comments made by some of the early exponents of reverse swing, but it has NO scientific basis to it whatsoever.
Wetting the ball may indeed help in the gouging process, but the importance of a dry, rough surface is now well understood by the current players who are often seen avoiding hand contact with the rough surface.
Another misconception is that reverse swing is more lethal because the ball swings more and late. It turns out the side-force magnitude and direction for reverse swing are comparable to those for conventional swing and for both types of swing, the ball follows a parabolic flight path so that most of the movement occurs in the latter part of the flight.
Bottom line: late swing is "built-in. My personal attempts at ball-tampering never really materialised.
By the time I figured it out, I found myself playing in California and our team captain - who was also the opening bowler - refused to let me tamper with the ball; he was convinced that my actions would "screw up" his beautiful outswing. The fact is that the condition of the "back side" of the ball the upper surface behind the seam in Figs 1 and 2 is not very critical.
So the perfect ball for conventional and reverse swing is one with one side very smooth and the other rough. There is also another advantage in creating a ball with a sharp contrast in surface roughness.
Contrast swing On a visit to the ECB National Cricket Academy last December, where I was invited to present my research on cricket ball aerodynamics, I realised that there was still some confusion regarding the definition of reverse swing. They had a practice session devoted to reverse swing with specially prepared balls one side deliberately roughened. Some of the bowlers swung the ball quite well and they thought in the reverse sense.
However, the ball generally had the seam straight up not angled and swung towards the smooth side. This was obviously not reverse swing and it was somewhat difficult for me to explain to the bowlers and coaches what was going on.
That is when I developed the new term: "contrast swing". So how is contrast swing different from conventional and reverse swing? In Fig 4 a , a ball with a contrasting surface roughness is flying through the air at a relatively low speed with the seam straight up.
In this case, the boundary layer over the upper surface separates relatively early in a laminar state while that on the bottom rough side becomes turbulent and separates later. This asymmetry results in a side force which makes the ball swing towards the rough side. If the ball is released at a much higher speed, the flow field is different as shown in Fig 4 b. In this case, transition occurs on both sides of the ball, but the turbulent boundary layer along the rough bottom surface is thickened and weakened in the same way that the seam weakens the turbulent boundary layer in reverse swing.
As a result the boundary layer on the rough side separates relatively early and the ball now swings towards the smooth side. Note that the actual critical bowling speed that determines which way the ball will swing is totally determined by the condition of the ball.
Superb examples of true contrast swing can be found in the second innings of the third Ashes Test, Flintoff to Matthew Hayden and Flintoff to Adam Gilchrist. The most exciting feature about contrast swing is that just about any bowler regardless of bowling speed can implement it in practice.
As most cricketers are aware, it is much easier to release the ball with the seam straight up, rather than angled towards the slips or fine leg. Thus, even mere mortals should be able to swing such a ball, and in either direction, since the bowling action is the same for both types of swing, the only difference being the orientation of the ball. In fact, the medium-pace "seam" or "stock" bowlers usually bowl with the seam in this orientation in an attempt to make the ball bounce on its seam so that it may gain sideways movement off the ground.
With a contrast in surface roughness, these bowlers could suddenly turn into effective swing bowlers, without any additional effort, thus confusing not only the batsman, but perhaps themselves as well. Another advantage of contrast swing is that it can be obtained even if the seam is completely "bashed-in" note that a prominent seam is critical for conventional and reverse swing.
If you doubt that a ball with a bashed-in seam can contrast swing, then tape over one half of a tennis ball and bowl it with the junction line straight up. There are two kinds of swing bowling that exist in cricket, one is the conventional swing and the other is the reverse swing.
This type of swing happens when the ball is new and generally lasts until the 15 th over of an innings. The conventional swing usually lasts longer with the red ball as compared to the white ball and the direction of the swing depends on the position of the seam. If the seam is pointed towards slip, it goes away from the batsman and if it is pointed towards fine-leg, it comes into the batsman.
When the ball is new, it zips through the air fast and the seam cuts the air in the direction it is pointed to and hence the movement happens. The conventional swing depends heavily on the weather conditions.
In overcast conditions that occur a lot in England, it swings more and for a longer duration whereas in dry conditions, it swings less and for a shorter duration. Contrary to conventional swing, reverse swing happens when the ball is old. As an innings goes on, the condition of the ball wears out and the fielding team works on the ball to keep one side shiny and allows the other side to be roughened up.
The ball after a certain amount of overs moves towards the shiny side and therefore it is termed as reverse swing. The reverse swing depends heavily on the conditions of the ground. If the pitch and the outfield are dry, there are more chances of the ball getting deteriorated. The fielding side applies sweat and saliva on one side of the ball and rubs it from that end to keep the shine intact.
That side of the ball becomes heavier and that is why it goes towards that side. The concept of reverse swing these days is found mostly in Test cricket and has almost lost its existence in ODI cricket. The introduction of two new white balls at each end in ODI cricket does not allow the ball to deteriorate enough to be suitable for reverse swing.
Earlier the whole ODI innings used to be played with one ball and from the 40 th over, the reverse swing used to make run-scoring difficult in the death overs. The loss of reverse swing is one of the reasons why so many high scores are made in ODI cricket these days. Since the inception of cricket, the game has witnessed several bowlers who made swing bowling an exhibition for the fans. Reverse swing is said to be discovered by the Pakistani bowlers which the bowlers from other countries picked up later.
Sarfaraz Nawaz from Pakistan was the first bowler who is given the credit of bringing reverse swing into the game of cricket. Recently, Umar Gul and Wahab Riaz have carried the baton of reverse swing bowling from the Pakistani contingent. Amongst the present bunch of bowlers, Mohammad Shami, Mitchell Starc, Vernon Philander and Tim Southee are the best exponents of reverse swing bowling. The art of reverse swing has always been a topic of debate.
Several allegations have been made on the players of ball tempering. Many times, players were caught altering the condition of the ball and worsen one side of the ball to achieve reverse swing.
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