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(Aerospace Engineer- Fill free to delete if unappropiate. I believe in overcast or humid condictions, the density of the air will tend to increase and change Re(Critical), varying the transition point for both turbulant and laminar flow around the ball. Having a white ball would likewise dissipate heat via heat transfer mechanisms around the ball. This could also cause a decrease in air density local to the (ball) surface, thus reducing transition points; which would also explain via similar theories why a red ball has a greater tendency to swing more.) I believe there is another section in wikipedia that mentions the mechanics of "swinging". —Preceding unsigned comment added by 220.127.116.11 (talk • contribs)
- I've shifted this from Fast bowling#Swing bowling, as it qualifies as WP:OR in its current form. These are interesting observations and certainly worth incorporating into the article if we can find appropriate references. --Muchness 17:25, 23 January 2006 (UTC)
- I've always put the humidity phenomenon down to the greater convective turbulence that occurs when the sun is shining. It seems (to me at least) that the fine differences that cause swing would need relatively smooth air. Anyway, isn't humid air actually less dense that dry air? http://www.usatoday.com/weather/wdensity.htm#humidity Robbak 06:27, 15 August 2006 (UTC)
This is just a new point on the mechanics. Though I can't find the relavent article online a study has shown that the difference between the turbulent and laminar flow seperation points on the ball doesn't provide enough force to "swing" the ball as much as is seen, though it helps the real effect. The physics behind it is the same as that of why a dimpled golf ball travels faster(and therefore further) than a smooth golf ball, and is the only theory which applies to all types of swing. Air moves faster over another layer of air than over anything else(the surface of a ball) and faster moving fluids(gases and liquids) have a lower dynamic pressure than slower moving fluids, this is utilised to "suck" the ball(like a vacuum) towards the lower pressure side. When the ball is new and both sides have a smooth surface, the seam is angled toward one side, this disturbs the air flow on that side creating turblent air which "sticks" to the ball more than the laminar flow on the other side(as stipulated in the article), but the difference is small, as the size of the ball is small, and so in turn, the lift force is small. BUT because there is a greater coverage of air on the turbulent side(and air moves faster over air) the next layer of air moves incredably fast over the "sticky" turbulent air than the small area of laminar flow. This creates a difference in dynamic pressure - higher pressure on the slower laminar side, and as everyone has learnt, everything moves from high to low pressure swinging the ball to the side the seam is angled to. The dimple effect occurs when the ball is slightly older and there is a shiny/smooth and rough side; no longer is the seem used to disturb the flow as this slightly ruins the effect. The rough side acts like the dimples of a golf ball, it traps the air in little pockets. This immediately creates a layer of air over the rough side of the ball and as the shiny/smooth side doesn't have these pockets and so no layer of air, the second layer of air moves faster over the rough side than the smooth side, changing the pressure, "sucking" the ball toward the rough side. Reverse swing occurs in the same manner, over time the rough side becomes too rough and the "dimples" become too big(this is why golf ball dimples are built to only a certain depth) and so the there no longer is the necessary layer of air over the rough side. To keep the shiny side shiny spit/sweat and other liquids are used to polish the ball, over time this builds up upon the shiny side of the ball, this causes the shiny side to expand(which can create a little more lift - more surface area), as anything does when soaked in water, but not uniformly. As it's not uniform "dimples" are created on the shiny side, which act in the same manner; trap air, creating a layer so the secondary layer moves faster over it, having lower pressure and now sucking the ball toward the shiny side. Over time conventional swing decreases as the rough side becomes too rough and the shiny side creates the appropriate dimples(so the forces become balance and therefore no swing) and then reverse swing has a greater force and dominates conventional swing. The differences in timing is simple and both types of swing can happen in one delivery because of it. Normal swing relies on the rough side having gouged out dimples which trap the air, while reverse swing relies on the shiny side's raised surface creating valleys which hold the air. The "dimples" immediately hold the air, even when the ball is still in the hand which is why the ball swings straight out of the hand, while the valleys on the shiny side only "holds" the air very temporarily when the ball is moving(as when something raised is moving there is a drag area created immediately behind it with no air). This means that to keep the valleys "full of air" to create the layer of air, the ball must be moving very fast, and because of the constant replacement of the air within the valleys it takes time for the force to build up which is why the ball swings late. And as the rough side still has some of the appropriate dimples you can have immediate conventional swing followed by reverse swing in one delivery. This is the only theory of swing that satisfies all laws of physics and can be applied to all types of swing and provides the force nessecary to swing the ball the amount that it does. I can write a more detailed and grammatically correct version for the article if needed, but mostly I'd just like the physics of this incorporated. Thanks - NEW EDIT: I'll rewrite this and incorporate it in a few days unless it receives any complaints in the area of physics, as i have been a fast bowler for a number of years and have seen and utilised this effect as well as learnt this in multiple classes the need of relavent articles is moot. Thanks
The discussion on turbulent vs laminar sides, and separation points, seems opposite to the way it should be. On the 'turbulent' side. would not the point of separation be more forward? To use an airfoil example, an aircraft wing stalls when the point of separation moves forward of the centre of pressure. Ie, the centre of pressure is in the turbulent region. -- Ch'marr 06:37, 6 May 2006 (UTC)
- 'Turbulent flow' and 'turbulance' or stalling, are two different things. An aerofoil will always have a turbulent 'boundary layer' between the air 'stuck' to the surface and the still air outside. A smooth, laminar flow is easy to break or disrupt, meaning that it breaks away from the surface easily. 'Turbulent flow', which means that the change between surface layer and ouside air takes place with turbulance, is much more robust. To give you an idea, these layers are generally less than a milimeter thick.
- 'Stalling' happens when the boundary layer completely breaks away from the surface, and no longer has any aerodynamic effect on that surface. This is akin to the seperation point. See the 'Science of swing' link in the article.
- Aerodynamics is full of counter-intuitive behavior like this.Robbak 06:16, 15 August 2006 (UTC)
Swing Bowling Tips
- A very slight change in your action (by tilting your body at release for instance) can completely negate swing. Try to stay upright and if you find yourself becoming tired and losing swing, take a break.
- Polish one side of the ball vigorously on your flannels and ask the fielders to do likewise. Some say rubbing sweat into the ball can increase swing. Experiment, but remain strictly within the laws and spirit of the game!
- A fuller delivery is more likely to swing but less likely to carry. A good length is often the best target for an away swinger and a fuller length for an inswinger.
- A little bit of swing is usually more effective than a pronounced amount as most batsmen cannot connect with a prodigously swinging ball. The old adage is that you only have to swing the ball a couple of inches to find the edge of the bat. If you are getting too much, try bowling with the seam straighter.
- Sometimes, "trying" to swing the ball is counter-productive. In swinging conditions the ball will swing on its own, so control it but don't "force" it.
- If you are no longer getting swing from the ball, try bowl cutters or breaks or varying your pace.
The article at http://content-uk.cricinfo.com/ci/content/story/258645.html expounds the view that reverse swing is when the ball swings away from the direction of the seam, not necessarily when it swings towards the shiny side. Should we make note of this? Lfh 12:40, 6 September 2006 (UTC)
- I don't think there's really a completely accepted definition that everyone agrees with. That article is certainly worth linking to as a reference though. -dmmaus 00:38, 7 September 2006 (UTC)
These two adjacent paragraphs are contradictory, and the first one is POV. Any suggestions as to how to make the article more consistent? "In the early days of reverse swing, Pakistani bowlers were suspected of ball tampering to achieve the conditions of the ball that allow reverse swing, but today they are considered to simply have been ahead of their time.
Controversy regarding reverse swing has never left modern cricket, as the Pakistani team was accused of ball tampering during the fourth test against England in 2006 when the ball began to reverse swing after the 50th over."
Glow worm64 05:39, 18 October 2006 (UTC)
- "Today they are considered" is pure weasel words, and the second is baseless, as there is no way for us to say that the ball tampering penalty was influenced by the reverse swing. JPD (talk) 13:41, 5 January 2007 (UTC)
No citation as yet. How about we delete the paragraph? Glow worm64 08:31, 6 April 2007 (UTC)
"Skilled bowlers can even make a ball swing one way, and then 'break' the other way upon bouncing, with an off cutter or leg cutter hand action." Surely a cutter can't swing, since the seam is scrambled - any movement in the air must be drift. Lfh 12:55, 6 December 2006 (UTC)
Swing Both Ways?
I'm certain from studying a lot of instances of so-called "S" reverse swing that the later part of the swing is caused by the spin on the ball as it strikes the pitch off the seam. It is almost impossible to make a ball swing one way then the other in the same trajectory. AbrahamCat (talk) 07:34, 3 October 2010 (UTC)
Deficiencies in the reverse swing section.
First of all reverse swing is not correctly explained; it has little to do with the seam and everything to do with the dynamics of golf ball dimples. When the ball gets old it develops what amount to 'holes' in the rough side. It is well established that the dimples in a golf ball smooth the airflow around it, making it go further, and a similar effect is at work here. The more smooth airflow over the 'rough' side makes it move through the air just like conventional swing, only towards a different side. This is why umpires suspect ball tampering, as a team will try to put holes in the rough side. Remember Afridi tucking into the ball during the one day series agianst australia? thats what he was trying to do, put holes in the ball to make it reverse. Also the 'S swing' bit doesn't stack up. It is possible to make the ball swing both ways in the same trajectory, but it has nothing to do specifically with reverse swing. 18.104.22.168 (talk) 09:26, 4 February 2011 (UTC)
Wrong explanation of swing
The explanation offered for the aerodynamics of swing are quite wrong.
"Turbulent air separates from the surface of the ball earlier than laminar flow air, so that the separation point moves toward the front of the ball on the turbulent side."
No! This is the exact opposite of what happens, as is well explained in many places on the web, many of which are linked to in the article! — Preceding unsigned comment added by 22.214.171.124 (talk) 15:05, 30 May 2012 (UTC)