Cricket ball swing-How to explain it

[tariq5]

Dear fellows since a long I have been puzzled by the cricket ball swing and reverse swing phenomenon. For fast bowlers when they(ball) throw ball(pitching with straight elbow vertically or near vertical movement of the arm) the ball swings may be towards the batsman(in swing) or away from the batsman(out swing). It is an Axiom among cricketers and cricket scientists world over that phenomenon is due to friction of air to one side of the ball(it is worth mentioning that most of the bowlers rub one side of the ball to keep the shine on it and keep the other side rough, that how the cheaters sometimes use bottle caps or others thing to rough one side).The older ball swing much more than the new. I am a medical doc but I have seen people swinging the soccer ball, ping pong ball and tennis ball and all the balls without keeping into the consideration the rough and smooth theory. I am, therefore, reluctant to accept this friction of air theory(may be it play slight part) but major element is how you throw the ball. All bowlers use two fingers on the seam or the ball(index and middle) and thumb on the other side of the .It is when one pushes the index or middle finger determines the swing of the ball(or some use angle of the arm during delivering the ball ).
Is momentum of body play some role or in fact that is rough shine theory. Can some body please explain it?

 

[Gokul43201]

With a cricket ball, it does have to do with friction. The relative flow velocity is greater on the smooth side and lower on the rough side. This difference in flow velocity provides a sideward "lift", following the Bernoulli principle.

With soccer or ping-pong, the difference in flow velocity is achieved by means of spinning the ball. However, with a cricket ball, a fast bowler does not spin the ball. He holds the seam essentially vertically and delivers the ball in that orientation. Sometimes, however, you can see a small amount of swing in the ball even when bowled by a spinner. This is due to the rotational effect, rather than the friction effect.

 

[tariq5]

Thanks Gokul
The actual problems now arise:
1-The brand new ball do swing(even first ball).
2-Isn't it against the "Bernoulli's Principle " The ball swings towards the rough side!
3-The same ball same techniques but with twist of fingers and or fingers the swing goes to wrong side(the reverse swing).
4-Not always the seam is vertical but most of the case it is much tilted.
5-If the air friction is too much it should cause the spin on the ball.
6-An irregular stone does swing.
7-Does spin causes deviation in the air or it stabilizes the path?After hitting the ground it does cause deviation.
My opinion is there is more force to one side of the ball cause it to swing.
Is that possible?

 

[vaishakh]

In that way Gokul, Why should Pakistanis do so much research in developing the reverse swing? you will get it if you reverse the position of the rough side and the smooth side. Please explain this in detail.
Tariq, some of your questions have answer in the above post.
I didn't understand the third question. As far as I framed the ball should swing to the smooth side as the rough side tends for more displacement than the smooth side. I don't know Bernoulli's principle? Comment if I am wrong. Have you heard anywhere that the ball swings to the rough side.

 

[tariq5]

vaishakh
The ball in certain circumstances swing both ways
swing towards the rough side yes
http://www.answers.com/topic/swing-bowling

To the smooth side many agree but many believe that it is due to heavier smooth side!
http://www.cricketworld.com/forum/forum_posts.asp?TID=243&PN=1

As the role of Bernoulli principle concerned the real phenomenon is against the Bernoulli principle.The fast bowlers tilt the seam to outer side(to first slip) and make the ball outswing. According to Bernoulli principle the roughness due to the seam should slow down the air on the outer side causing more velocity to smooth side. As Bernoulli principle states that higher speed of fluid decreases the pressure so should the ball swing inward, but in reality it swing outward!

 

[tariq5]

Since there is no hot discussion for this topic I would i like to state my personal views not because I am 100% sure they are correct but at least that would trigger the reactions.
The cricket ball swing is of two types first before the ball hitting the ground and second after it has hit the ground. The in swing or outswing or reverse swing is that what we observe after the ball hitting the ground. But many explanations like "Bernoulli's principle",friction of air to rough surface(the braking effect), heavier shiny side(due to application of spit or saliva etc.) only referred to swing before the ball hitting the ground. First of all it is not a very big swing especially for short pitch or good length ball and not very frequently observed except in full pitch ball or yolkers. Bernoulli principle fails even to explain the air lift by the aero planes what is popularly thought. The newer views that it is the angle of attack of air by the wings the engine power and many other Newton’s laws operate much more than Bernoulli principle. Even in cricket ball the angle of delivery to a specific spot determines the swing in the air.

The second part is the swing of the ball after hitting the ground and what I have observed that it mainly depends on the part of the part it hit the ground first. For example for outswing as the seam is about 10 degree tilted towards the first slip if the ball is delivered fairly straight (without spin or swing too much in the air) the more chances that it will hit the seam to the ground first. After hitting the ground the speed of the seam part of the ball tremendously falls as compare to the upper surface the ball moves out wards. The roughness has little to do any thing except if it is present it act like a extra seam like effect( providing a good grip for holding and throwing the ball or a good rough surface for the ball to act like a break). So the movement of the ball after hitting the ground mostly depends upon the movement of the fingers, arm and holding of the ball.

 

[abhishek_jhaj]

Swing of a ball

Hi All,

Please remove all confusion from your minds.

Please note that normal swing has nothing to do with Bernoulli principle. The principle is only applicable if their is smooth or turbulent flow on both sides of the ball i.e. similar viscosity. If the ball is thrown at low speed both sides of the ball have smooth flow. If the ball is thrown with high speed, both sides of the ball have turbulent flow. There are also speed ranges in which flow may be turbulent or smooth. These speeds are given by Reynolds number. A medium pacer uses this middle critical region of speed, where the flow may be smooth or turbulent, to swing the ball. The rough side of the ball has turbulent flow whereas the smooth side of the ball has smooth flow in this critical range of speed. Hence, air on the rough side fails to catch up with the air on the smooth side creating a low pressure region on the rough side. This tends to deviate the ball on the rough side in normal swing.

Reverse swing can only occur when both sides of the ball has turbulent flow. This is only possible at high speeds. Pakistani bowlers did research to achieve these high speeds only and nothing else. Wasim Akram even advised Irfan Pathan to achieve high speeds back as always after the T20 world cup. Bernoulli principle comes into effect at these high speeds and it makes air speed low on the rough side and fast on the smooth side. Faster speed on the smooth side leads to air being vanished more quickly on the smooth side creating a low pressure region as explained by Bernoulli principle. Hence, the reverse swing. Also, reverse swing happens late in a ball's trajectory as opposed to normal swing because ball has to first accumulate considerable portion of air to achieve turbulence. It is also possible for a ball to first swing in a normal way and then reverse its swing giving the delivery an S-shape. These S-shape swings are generally delivered by the likes of Glenn McGrath.

Also, with regard to ball deviation after pitching please note that these are due to off cutter or leg cutter hand action of the bowler and has nothing to do with the swing. Cutter action is achieved in the same way as spinner action. In fact, a cutter of a fast bowler is a spinner at high speeds. Venkatesh Prasad was a master in delivering such cutters.

Last but not the least, please note that normal swing is not achieved by very fast bowlers. Shoib Akhtar was the fastest bowler at one time but he didn't achieved considerable swing. He was often hit by Sachin Tendulkar at high speeds who used his pace to his advantage.

Also, Magnus Effect comes into play if a spinner is bowling as opposed to Bernoulli principle. There is also a phenomenon called reverse Magnus Effect. I can explain these if required.

-Abhishek Jha

 

[rcgldr]

Two links with differing explanations about Magnus Effect. The second link includes cricket.

Bernoulii based explanation, diagram of "top spin":
http://en.wikipedia.org/wiki/Magnus_effect

Detached air flow explanation, diagram of "back spin":
http://www.geocities.com/k_achutarao/MAGNUS/magnus.html

Based on my "research" regarding wing's, it's probably a combination. In the case of wings, initially you have attached laminar flow, which transitions into turbulent flow and detaches, then reattaches after the transition, leaving a transition "bubble" on the wing. Do a web search for "oil flow test glider", and you'll find it's common practice for magazine reviews of gliders to do oil flow tests to observe the tansition bubble and see if adding turbulators would improve lift to drag ratios by altering the location and size of the transition bubble. Roughing up the surface works also.

 

[jonny888]

I'm afraid that I am not a physicist nor a mathematician but I am a cricket enthusiast and have worked in meteorology.

I have watched cricket matches for many decades and my personal theory concerning a swinging cricket ball has to do with its rate of deceleration.

I have seem balls which after pitching outside the line of the stumps (and left alone by the batsman) have swung quite dramatically before reaching the wicketkeeper, sometimes evading even his dramatic dive.

The idea of high humidity and overcast conditions suggests that the air contains greater concentrations of minute water droplets than air at higher temperatures. I wonder if this helps to decelerate the ball more quickly than in drier air, and the effect is more pronounced when the sides of a ball vary in smoothness?

In the UK, on a cool and cloudy day with an air temperature of maybe 16C the humidity can be regularly between 90% and 85%. On a cloudy day with a temperature of 25C the humidity in the UK is rarely going to be above 65%.

I wonder if anyone has experimented by bowling in very misty conditions (say as the sea fog is about to roll in at Scarborough) where the humidity would be 95% and above? I know the conditions would not allow a first class game to proceed, but I was thinking more of just practice bowling to see if the ball swings even more than normal.

This would explain the faster bowling swinging less, because the ball has only a limited time in the air and is unlikely to decelerate more than a few mph.

I do realize that this may seem a rather questionable explanation and please feel free to pooh-pooh the whole idea.