swing bowling has little to do with the bernoulli principle but is related to laminar and turbulent flow.
bernoulli principle or theorem deals with fluids(air is one of them) passing from a narrow cross sectional area to a wider cross sectional area and the resultant pressure differences it creates. it can be brought into the discussion of swing bowling but most experts believe it has little effect.
more reasonable is the characteristics of the air flow pattern around the ball. laminar or turbulent.
at speeds less than 85 mph some take it upto 90 mph the flow around a new ball should be laminar. whether it is or not is quantified by the reynolds number extremely difficult to calculate in the cricket field scenario and hence the discrepancy.
Normal swing (conventional swing)
at less than 85 mph the flow around the ball is laminar and the swing bowler introduces the seam or roughness on one side to make the flow turbulent. this makes the ball move away from the shiny surface. remember for in swing therefore the ball has to be angled with the seam in the direction of legslip and the shiny surface on the offside of the right handed batsman. an important point here is that to do so - that is to keep the seam straight you have to impart revolutions on the seam either backwards or forwards, which depends on which swing you intend to impart and therefore the grip and the wrist action - i am not going into that here but will be pleased to do so if somebody asks.
this makes it possible to have laminar flow on the offside of the ball and turbulent flow on the onside (right handed batsman) and the ball swings towards the turbulent flow. it is akin to rowing - when you want to turn your boat to the right(assuming you are sitting looking in the direction of travel) you keep your right oar still in the water and furiously row with your left one) this ensures more turbulent flow on your right because the oar is stationary and kind of laminar flow on the other side (depending on your rowing expertise) and the boat turns right.
it is the other way round for outswing.
reverse swing
at speeds greater than 85 mph, 90 according to some, there is turbulent flow on both sides of the ball. the seam is important here because it causes the airflow to separate earlier on the side of the seam and the ball swings towards the side of the later separation. therefore you can have the inswingers grip and ball positioning (shiny surface, or what is left of it, offside and the seam positioned angling towards legslip, classical inswinging grip and position) but the seam causes it to swerve towards the offside because of differential separation of airflow i have mentioned earlier and therefore foxing the batsman. it is more difficult to achieve and tends to be more pronounced in hotter weather and late (for yet unevaluated reasons). the speed of the delivered ball is more important and has to be more than 85 mph atleast and preferentially 90 mph. also uneven wear on the rough side exaggerates the above mentioned flow separation and causes more reverse swing.
the weight of the ball has nothing to do with it as far as current physics can explain ( gouravk note) and the practice of taping the ball has nothing to do with weight but all to do with differential airflow around it.
so far no satisfactory physical explanation has been put forward to why it swings more in overcast humid conditions but the fact that laminar flow is only dependant on the viscosity and turbulent flow on viscosity and density may play a part. wet humid weather has more water vapour molecules and hence is more dense so the turbulent flow characteristics may be exaggerated. not proven but postulated.
if you guys have any more questions regarding this will be glad to answer IF i can. hope this is interesting.
AuthorTopic: Unravel the mystery of reverse swing (Read 931 times)
June 28, 2006, 10:10:12 PM