Drift
- Thread starter someblokecalleddave
- Start date
You make it sound so simple!
Well the description can be as simple or as complex as you want it to be, but there is nothing inherently complex about the phenomenon, the only problem is that a number of cricket writers don't really understand it themselves and can say misleading things.
Spiderlounge
Member
Did someone say they found the ball drifted more when wet? I may have figured out why this is...
I'm sure you'll mostly be aware that swing bowlers tend to find overcast conditions help them swing the ball, but the traditional explanation for this (that the air is more humid and therefore more dense) strikes me as scientifically wrong. I think what's actually happening is the air is LESS humid, but more dense as a result.
Let me start off with a simple fact: at a given temperature and pressure, a set number of air molecules will always occupy the same volume. The density of the gas is therefore dependent on the mass of the molecules. Water vapour molecules are actually less heavy than the average air molecule:
Molecular mass:
Nitrogen (N2) = 2x14 = 28 (~80% of air)
Oxygen (O2) = 2x16 = 32 (~20% of air)
Average for air = 0.8x28 + 0.2x32 = 28.8
Water vapour (H2O) = 2x1 + 16 = 18
Now air's ability to absorb water vapour increases with temperature, so if conditions are overcast the air cools down and some of the water will condense out of it, making the air more dense. So if the ball's wet because the outfield is wet (because it's rained) one can assume there's a certain amount of cloud cover, so the air will be more dense and drift will increase.
I'm sure you'll mostly be aware that swing bowlers tend to find overcast conditions help them swing the ball, but the traditional explanation for this (that the air is more humid and therefore more dense) strikes me as scientifically wrong. I think what's actually happening is the air is LESS humid, but more dense as a result.
Let me start off with a simple fact: at a given temperature and pressure, a set number of air molecules will always occupy the same volume. The density of the gas is therefore dependent on the mass of the molecules. Water vapour molecules are actually less heavy than the average air molecule:
Molecular mass:
Nitrogen (N2) = 2x14 = 28 (~80% of air)
Oxygen (O2) = 2x16 = 32 (~20% of air)
Average for air = 0.8x28 + 0.2x32 = 28.8
Water vapour (H2O) = 2x1 + 16 = 18
Now air's ability to absorb water vapour increases with temperature, so if conditions are overcast the air cools down and some of the water will condense out of it, making the air more dense. So if the ball's wet because the outfield is wet (because it's rained) one can assume there's a certain amount of cloud cover, so the air will be more dense and drift will increase.
someblokecalleddave
Well-Known Member
Seriously suggest you read The Bowlers Art; the testing and reasoning behind drift, swing, swerve...whatever in the book is pretty convincing once you also think through your own experiences. You'll find after reading it that the 'air-moisture' argument for swing and drift isn't right.
The writer instead, after testing, has found that the ability of the pitch to radiate heat affects the ability of the ball to move in the air. After it has rained, or if there is cloud cover, the pitch does not absorb and radiate heat to the extent than when the pitch is dry and there is no cloud cover. The turbulence created by the radiated heat interferes with the cricket ball's aerodynamic interaction with the air thus suppressing swing/drift, when there is cloud cover there is less radiated heat and thus less turbulence. This explains why swing and drift can occur in all countries to the same extremes despite there being differences in humidity between all those countries
Note that the ability of the pitch to radiate heat is dependent on the difference between the temperature of the pitch and the surrounding air.
If I haven't explained it right I wholeheartedly recommend the book to fill in the complete picture...can get a bit technical but it may be something that you'll understand straight away given your post!
macca
Active Member
So that's what Wilkins was on about. You explained it a lot better and far more concise than he did in 'the bowlers art'.
S
Unfortunately sometimes you need a kiwi to translate a kiwi...
macca
Active Member
Maybe you are right. Wilkins worked out his fellow kiwi Grimmetts "mystery ball" from Grimmetts books. Grimmetts biographer, an Aussie, missed it altogether.
someblokecalleddave
Well-Known Member
I wish Physics had been like this when I was at school and that I played cricket at the time and was a spin bowler. I think Spiderlounge has mentioned Torque before and watching this it seems to me that it has a bearing on what we're doing or am I completely wrong?
I don't think it would have any bearing on drift (perhaps a negligible amount at best) but I'd imagine it would when talking about how a spinning ball interacts with a pitch on impact. The key for drift is more along the line of fluid dynamics (aerodynamics), that link posted earlier as how a rotating object reacts with air is more what we're after.
SLA's description was really concise and nailed it as far as I'm concerned; basically if I bowl a 'UFO' delivery (a ball spinning parallel with the pitch, with perfect seam position for the spin) the ball will start drifting straight away, if I ball a spinning ball square on (ball spinning perpendicular to the pitch, again with perfect seam position) the ball will only start to drift as it drops later in its flight.
Again the keys for drift remain big revs and seam position...the right weather/temperature balance always help as well.
Further justification to your 'radiated heat' argument here: http://www.bbc.co.uk/news/science-environment-18262145
Sorry Dave, if you want to move this across out of the spin section feel free
someblokecalleddave
Well-Known Member
No that's fine Tony useful for the upright seam Flipper bowlers.
Spiderlounge
Member
I think there's a big difference in that the wheel is tethered and a cricket ball isn't, so while the ball may move in the air it's a sideways force over the whole ball rather than a rotation caused by torque. Like Leftie600 said it's more relevant to what happens when the ball pitches. I could be wrong though, I have been before! I'd advise you to steer well clear of trying to understand gyroscopes and the science behind them, I did a project on them at A-level and they're very difficult to get your head around.
Andrew Bourne
Member
cheers for the research guys, i am quite a big drifter of the ball, and had never had any idea of the mechanics behind it. I had learned somewhat how to gain some sort of control, but had 0 idea of the actual science. Thanks for the read!
someblokecalleddave
Well-Known Member
So without all the physics, what do you reckon that you do that gets you the drift and... can you bowl the same kind of ball with or without the drift at will?
Andrew Bourne
Member
It basically works on the principle of what has been mentioned before. The more topspin on it, the later it goes, the more sidespin, it goes earlier, and a bit further... but easier to play because its from the hand. However, its not something that i can say... ok start this off stump and make it drift to leg... there's still a chaotic element just as there is for a fast swing bowler.
Also, i am a fairly big spinner of the ball, and the harder i rip it the better it goes, as well as making sure the seam isn't scrambled (doesn't tend to drift as much... not sure why as it doesn't work on the same principles as swing bowling shown by the research you guys have done, could have more to do with the fact that there is a better release... or the shiny/rough side of the ball creating drag as well.)
It tends to drift more the older the ball is, and i get more drift with the white ball than i do the red usually (not sure why this is the case... maybe its just more noticeable because batsmen are being more aggressive.... therefore deceives them in flight more often)
However, on the whole... when i am getting the ball to drift... it pretty much goes every ball i bowl, just a varying amount.
Staying as far away from any physics element as possible with that response, talking purely on the feel aspect from bowling.
Also, i am a fairly big spinner of the ball, and the harder i rip it the better it goes, as well as making sure the seam isn't scrambled (doesn't tend to drift as much... not sure why as it doesn't work on the same principles as swing bowling shown by the research you guys have done, could have more to do with the fact that there is a better release... or the shiny/rough side of the ball creating drag as well.)
It tends to drift more the older the ball is, and i get more drift with the white ball than i do the red usually (not sure why this is the case... maybe its just more noticeable because batsmen are being more aggressive.... therefore deceives them in flight more often)
However, on the whole... when i am getting the ball to drift... it pretty much goes every ball i bowl, just a varying amount.
Staying as far away from any physics element as possible with that response, talking purely on the feel aspect from bowling.
someblokecalleddave
Well-Known Member
No that's fine, it does seem that you can get too wrapped up in the physics and the basics are spin it hard, but I'm still interested in the fact that if it's that simple e.g. spin it hard, there seems to be the potential to choose between getting the ball to drift and not doing?
Andrew Bourne
Member
if i don't want it to drift that much/ at all, i just scramble the seam a little...