Entropy and a half m v squared

I am sure that this is the first article in Baggy Green to attempt to combine cricket and physics. Cricket can be used to explain the physical laws of nature but I want to lead you through two important Laws of Physics as applied to cricket

 The first section, which discusses the First Law of Thermodynamics, is a sealed section. It has the rude subtitle “Balls Keeping Low.” The second section applies the Second Law of Thermodynamics to the referral system now used in test cricket. Is this the first crack in the second Law of Thermodynamics? Is the second Law still a universal Law?
 

Ever noticed how batsmen are always late on clamping down on a ball keeping low? I ask you. “Why is it so”? I can think of two reasons.
 

 The first is obvious. He has to change his stroke at the last second, but we have all seen a batsman bowled by a “shooter” before he has had time to change his stroke. He departs with a wry grin because he knows that the bowling team will also have to bat on this pitch.


The other reason that a ball keeping low hurries a batsman is that a shooter does not lose as much speed as it hits the ground as a delivery that bounces normally. When a ball hits the pitch its speed reduces markedly. A delivery at 130 km/hour leaves the pitch after bouncing at about 90 to 100 km/hour. I reckon when a ball “shoots” the reduction in speed is much less. There is a reduction in the reduction so to speak. I remember batting on wet pitches back in the uncovered days. There were lots of “popping” deliveries that would lift alarmingly, but slowly. Letting them go was the secret to success. Keeping your hands low was the key.


I can come up with quite a few interesting reasons for these phenomena but you will have to have done some physics to understand them fully. If you could not get into University here in Melbourne and had to go to Monash, the southern outreach program of Kew Cottages, most of it will make sense. If you could only get into La Trobe (this was where the more dangerous people from the Mont Park Psyc home were housed back in the 70s and 80s) get some help. If you could only get into Victoria Uni out there on the Maribonong you are in real trouble. Most people will not remember the Newmarket Cattle yards that were just across the river from Victoria University. They shut the cattle yards down as the lecturers found it too difficult to tell the difference between the students and the cattle. I mean the cattle were often better bred, were more intelligent and certainly had cleaner personal hygiene habits.


Why does the ball slow when it hits the pitch? Remember the first Law of Thermodynamics? Energy cannot be created or destroyed. It can only be changed from one form to another. We have the ball travelling forward. This forward motion gives it some kinetic energy (E = ½mv squared). The ball hits the pitch and loses some speed. Where has this kinetic energy gone? Can we come up with some reasons why the loss of energy is smaller when the ball keeps low?


First, the ball makes a sound when it hits the pitch. This requires some energy and therefore takes some kinetic energy away from the ball. I wonder if a bumper makes more noise than a shooter. Interesting point really and I don’t have an exact answer but we now have Channel Nine’s snicko which would allow this point to be clarified.


The friction generated when the ball hits the pitch will heat up the ball and the ground. Once again the energy required to do this will rob the ball of some of its kinetic energy. If they can calibrate the infra red cameras they use for the “hot spot” this could be calculated.


On a soft wicket the ball digs in and “pops”. As it embeds itself into the ground the vectors of force acting on it change. As there is now more material directly in front of its direction of motion it will be forced upwards. Frictional influences become more important and I am willing to bet more energy will be lost to heat generation. Bring on the “hot spot” camera.

 
As the ball rises some of the kinetic energy is transferred into potential energy. The higher the bounce, the more kinetic energy will be lost to potential energy while a “shooter” will not lose very much speed at all in this way.

I reckon one of the major factors is something that you probably haven’t thought about yet. When a ball hits the pitch, the ball will start to rotate in the direction of the movement of the ball. Some of the kinetic energy of the ball has been transferred into rotational energy. I think this will be a major fractor. I reckon a “shooter” will not be rotating very much at all, but a “popper” will be rotating furiously. The equations for rotational momentum are well within a year 12 physics student. Look them up and have a go at applying the first Law of Thermodynamics to a cricket ball.

With the wonderful cameras we have at the test matches you can see the ball rotating. This rotation can be measured. What about Cricket Australia giving me a grant to investigate Balls Keeping Low? I would need to go over to India and Pakistan where the bounce is generally lower but hey, science is never easy.

So the next time you see a ball keeping low, smile to yourself and say, “rotational momentum is the key there”


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The referral system now used in test cricket has been judged a “qualified success” but does it contravene the second Law of Thermodynamics? Most of you have seen what happens when a batsman has been given out, but calls for a referral. The fielding team has been celebrating; high fives everywhere. Then comes the request for a referral.

 
What is the second Law of Thermodynamics? Very roughly entropy (or disorder) always increases. A pack of new playing cards just taken out of their packet are in a very ordered state. Throw them in the air and they will become disordered. When I was at University we watched a video of a clock pendulum swinging backwards and forwards. It was impossible to tell if the film was going backwards or forwards. A physicist will tell you that the laws of physics work just as well with time going backwards as they do with time going forward. An egg was dropped just in front of the clock. It smashed into pieces i.e. became more disordered. Suddenly the “arrow of time” became apparent. I have watched some spectacular videos of the space shuttle docking on the space station Once again, without some observable increase in entropy, you cannot tell if the shuttle is docking or leaving the space station. The “arrow of time” is not apparent.

 
With the referral system the batsman is sometimes let off and the fieldsmen slink back to their original ordered position. Time has moved forward but (admittedly in a very rough way) entropy has decreased and to some people THIS IS JUST NOT RIGHT.

 
I thought about this while sitting at the Adelaide Oval with our glorious editor and Neville Turner (a retired Law Professor). Now I am all for technology. Being a dentist I had a scientific education where getting the correct answer was paramount. There usually was a simple correct answer. Shades of meaning or values did not exist. Your crown either fitted or (too often in my case) it did not fit. This parallels most umpiring decisions on a cricket field. I think that referral system gets the decisions correct and technology, generally, helps to expose, and curb poor player behavior. Neville Turner hates the referral system and thinks it is completely unnecessary if players took their responsibilities seriously.

 
He believes that players should walk when they are out and not appeal when they know it’s not out. I find it interesting that a Law Professor appeals to the spirit of cricket, our sense of fair play, our better side, rather than agitate for new laws, regulations or technology. He has a point of course but I know that Neville is a romantic rather than a physicist. To Neville being able to take the bad decisions with grace is the essential part of what we call “the Spirit of Cricket”. To people like Neville the game as a whole is more important than an umpiring decision. This is something I have great difficulty with. As an umpire I fret about the mistakes I make. I would love to have technological backup. As a dentist I worry about the treatment I provide for my patients but the dental profession has been responsible for a complete revolution in the dental health of Australians in the last 40 years. It is the wider picture that is the important thing.

 
Neville wants to inspire cricketers to keep the tradition of civility on the cricket field strong while I want to have 20 cameras trained on them so they know they better behave.

 

Baggy Green   Journal of Australian Cricket.  Edited by Bernard Whimpress

This is Australia's only serious cricket journal. Get it from Roger Page(check out his page on the site) or email the editor bernardwhimpress@gmail.com