## A Physicist’s Tribute to Shane Warne (1969-2022)

Posted in Cricket, The Universe and Stuff on March 4, 2022 by telescoper

I was shocked to see just now the news that legendary Australian legspinner Shane Warne has passed away suddenly at the age of just 52. I always admired his bowling hugely no doubt partly because having tried to bowl leg-breaks myself I have some idea how difficult it is to do well! I thought as a tribute I would rehash a piece I posted about 12 years ago about the prodigious amount of spin Shane Warne was able to generate.

For those of you not so familiar with cricket here’s a clip of another prodigious spinner of the ball, Australia’s legend of legspin Shane Warne:

For beginners, the game of cricket is a bit similar to baseball (insofar as it’s a game involving a bat and a ball), but the “strike zone” in cricket is a physical object ( a “wicket” made of wooden stumps with bails balanced on the top) unlike the baseball equivalent, which exists only in the mind of the umpire. The batsman must prevent the ball hitting the wicket and also try to score runs if he can. In contrast to baseball, however, he doesn’t have to score; he can elect to play a purely defensive shot or even not play any short at all if he judges the ball is going to miss, which is what happened to the hapless batsman in the clip.

You will see that Warne imparts considerable spin on the ball, which has the effect of making it change direction when it bounces.  The fact that the ball hits the playing surface before the batsman has a chance to play it introduces extra variables that you don’t see in baseball,  such as the state of the pitch (which generally deteriorates over the five days of a Test match, especially in the “rough” where bowlers have been running in).
A spin bowler who causes the ball to deviate from right to left is called a legspin bowler, while one who makes it turn the other way is an offspin bowler. An orthodox legspinner generates most of the spin from a flick of the wrist while an offspinner mainly lets his fingers do the torquing.

Another difference that’s worth mentioning with respect to baseball is that the ball is bowled, i.e. the bowler’s arm is not supposed to bend during the delivery (although apparently that doesn’t apply if he’s from Sri Lanka). However, the bowler is allowed to take a run up, which will be quite short for a spin bowler, but long like a javelin thrower if it’s a fast bowler. Fast bowlers – who can bowl up to 95 mph (150 km/h) – don’t spin the ball to any degree but have other tricks up their sleeve I haven’t got time to go into here. A typical spin bowler delivers the ball at speeds ranging from 45 mph to 60 mph (70 km/hour to 100 km/hour).

The physical properties of a cricket ball are specified in the Laws of Cricket. It must be between 22.4 and 22.9 cm in circumference, i.e. 3.57 to 3.64 cm in radius and must weigh between 155.9g and 163g. It’s round, made of cork, and surrounded by a leather case with a stitched seam.

So now, after all that, I can give a back-of-the-envelope answer to the question I was wondering about on the way home. Looking at the video clip my initial impression was that the ball is deflected  by an angle as large as a radian, but in fact the foreshortening effect of the camera is quite deceptive. In fact the ball deviates by less than a metre between pitching and hitting the stumps. There is a gap of about 1 metre between the popping crease (where the batsman stands) and the stumps – it looks much less from the camera angle shown – and the ball probably pitches at least 2 metres in front of the crease. I would guess therefore that it actually deflects by an angle less than twenty degrees or so.

What happens physically is that some of the rotational kinetic energy of the ball is converted into translational kinetic energy associated with a component of the velocity  at right angles to the original direction of travel. In order for the deflection to be so large, the available rotational kinetic energy must be non-negligible compared to the original kinetic energy of the ball. Suppose the mass of the ball is $M$, the translational kinetic energy is $T=\frac{1}{2} Mv^2$ where $v$ is the speed of the ball. If the angular velocity of rotation is $\omega$ then the rotational kinetic energy $\Omega =\frac{1}{2} I \omega^2$, where $I$ is the moment of inertia of the ball.

Approximating the ball as a uniform sphere of mass $M$ and radius $a$, the moment of inertia is $I=\frac{2}{5}Ma^2$.  Putting $T=\Omega$, cancelling $M$ on both sides and ignoring the factor of $\frac{2}{5}$– because I’m lazy – we see that the rotational and translational kinetic energies are comparable if

$v^2 \simeq a^2\omega^2,$

or $\omega \simeq \frac{v}{a}$, which makes sense because $a\omega$ is just the speed of a point on the equator of the ball owing to the ball’s rotational motion. This equation therefore says that the speed of sideways motion of a point on the ball’s surface must be roughly comparable to speed of the ball’s forward motion. Taking $v=80$ km/h gives $v\simeq \frac{80 \times 10^3}{60 \times 60} \simeq 20$ m/s and $a\simeq 0.036$ m gives $\omega \simeq 600$ radians per second, which is about 100 revolutions per second. This would cause a huge deviation (about 45 degrees), but the real effect is rather smaller as I discussed above (see comments below). If the deflection is actually around 15 degrees then the rotation speed needed would be around 30 rev/s.

This estimate is obviously very rough because it ignores the direction of spin and the efficiency with the ball grips on the pitch – friction is obviously involved in the change of direction – but it gives a reasonable ballpark (or at least cricketground) estimate.

Of course if the bowler does the same thing every time it’s relatively easy for the batsman to allow for the spin. The best  bowlers therefore vary the amount and angle of spin they impart on each ball. Most, in fact,  have at least two qualitatively different types of ball but they disguise the differences in the act of delivery. Offspinners typically have an “arm ball” which doesn’t really spin but holds its line without appearing to be any different to their spinning delivery. Legspinners usually have a variety of alternative balls,  including a topspinner and/or a flipper and/or a googly. The latter is a ball that comes out of the back of the hand and actually spins the opposite way to a legspinner while being produced with apparently the same action. It’s very hard to bowl a googly accurately, but it’s a deadly thing when done right.

Another thing also worth mentioning is that the rotation of the cricket ball also causes a deviation of its flightpath through the air, by virtue of the Magnus effect. This causes the ball to curve in the air in the opposite direction to which it is going to deviate on bouncing, i.e. it would drift into a right-handed batsman before breaking away from him off the pitch. You can see a considerable amount of such movement in the video clip,  away from the left-hander in the air and then back into him off the pitch. Nature clearly likes to make things tough for batsmen!

With a number of secret weapons in his armoury the spin bowler can be a formidable opponent, a fact that has apparently been known to poets, philosophers and astronomers for the best part of a thousand years:

The Ball no Question makes of Ayes and Noes,
But Right or Left, as strikes the Player goes;
And he that toss’d Thee down into the Field,
He knows about it all — He knows — HE knows!

The Rubaiyat of Omar Khayyam [50]

## A Trophy for Glamorgan!

Posted in Cricket with tags , , , on August 19, 2021 by telescoper

Just a brief post but I thought I’d say something about Glamorgan’s cricketers, because it’s such a rare event and I might not get the chance to write a similar post for a while!

This evening Glamorgan actually won a trophy! They beat Durham by 58 runs in the final of the Royal London One-Day Cup (a 50 overs competition) which was held at Trent Bridge. That’s the first competition they have won since 2004.

Glamorgan batted first and managed to score 296 for 9 with skipper Kiran Carlson- who is only 23 – scoring 82 and the last pair, Carey and Hogan, putting on 33 runs. Durham were never ahead of the run rate but Sean Dickson kept them in with a chance until he ran out of partners and was sreanded in 84 not out, with the last four wickets falling for just 12 runs to leave them on 238 all out with one ball less than five overs remaining. The last wicket to fall was the hapless Chris Rushworth, out first ball caught by wicket-keeper Tom Cullen.

People will say that the Royal London Cup has been devalued by the absence of players on account of The Hundred, but that has affected all the teams and the competition has produced some really good games and I am delighted for the players to have won a trophy at last. Congratulations to them!

(It’s still not proper cricket mind….)

## Back in the office!

Posted in Biographical, Cricket, Maynooth on August 16, 2021 by telescoper

Well, as promised yesterday I went back into my office at Maynooth University this afternoon. I didn’t achieve very much apart from resetting some of the sophisticated equipment (see above) but it’s a start…

To be honest I was a little distracted by the cricket at Lord’s where there was a remarkable turnaround in Indian’s favour on the last day. Looking like they were going to struggle to save the game with six wickets down for 181, a lead of just 154 overnight, and losing two quick wickets in the morning, India went on to declare on 298 for 8, then bowled England out this evening for just 120. It’s been an excellent Test Match, full of twists and turns, ending in a result that seemed very unlikely at the start of the day.

Call me old-fashioned but you can’t beat Test cricket. Nothing compares to it!

## Back to Civilisation

Posted in Biographical, Cardiff, Covid-19, Cricket, GAA, Maynooth with tags , , , on July 24, 2021 by telescoper

So last night I returned safely from Cardiff to Ireland via Birmingham. Travel both ways was relatively uneventful. There can’t have been more than 30 people on the flight in either direction. I did however almost screw up the return flight by omitting to fill in the obligatory Covid-19 passenger locator form which I hadn’t realised is now online-only. I only found out that I had to do it before they would let me on the plane, resulting in a mad scramble with a poor phone connection to get it done. After a few goes and quite a bit of stress I succeeded and was allowed to board, conspicuously the last passenger to do so. We still managed to leave early though, and the short flight to Dublin – passing directly over Ynys Môn was relaxing and arrived on schedule; the immigration officer scanned my new-fangled Covid-19 vaccination certificate but wasn’t interested in the passenger locator form that caused me so much stress on departure.

I returned to Cardiff to take a bit of a break, to check up on my house and also prepare to move the rest of my belongings to Ireland. I was relieved when I got there last week that everything was basically in order, although there were lots of cobwebs and a very musty smell, which was hardly surprising since I hadn’t been there for 15 months. The inside of the fridge wasn’t a pretty sight either.

One night last week after meeting some friends for a beer in Cardiff I walked back via Pontcanna Fields and saw, much to my surprise, Camogie practice in progress in the twilight:

The logistics of my planned removal proved a bit more complicated than I expected but eventually I cracked it and all the arrangements are now in place. I should receive delivery here in Maynooth next month. I’m doing it on the cheap as a part-load, which is why it will take a bit longer than usual.

Cleaning and packing was very hard work owing to the intense heat over the last week or so – it was regularly over 30° C – during the day, so I took quite a few siestas. My neighbours tell me it’s been much the same here in Maynooth, although it is a bit cooler today, around 20° with a very pleasant breeze.

Despite the hard work it was nice to have a change of scenery for a bit and also to meet up with some old friends from Cardiff days. Everyone has been in a state of limbo for the last 18 months or so, and although we’re not out of the woods yet there are signs of things coming back to life. When I went to Bubs in Cardiff for a drink last week it was the first time I’d been inside a pub since February 2020!

Incidentally, most people I saw observed social distancing, wore masks, etc. The rules in Wales are still fairly strict. Although open for indoor service, bars and restaurants seem to have few customers. Some people on trains to and from Birmingham didn’t wear masks. One group of unmasked and obnoxious English passengers on my return journey were loudly boasting how backwards Wales was compared to England, where the rules have relaxed despite a huge surge in cases. I moved to another carriage.

The only other thing I managed to do was attend a Royal London One-Day Cup match at Sophia Gardens between Glamorgan and Warwickshire in the baking heat of Sophia Gardens. It turned out to be a good tight game, with Glamorgan winning by 2 wickets courtesy of two consecutive boundaries. Most of the time I was sitting there in the shade I was thinking how glad I was not to be fielding in such conditions.

One thing that was very noticeable during my stay in Wales was that it was very hard to get fresh salad vegetables and the like. That may be partly due to weather-related demand or it may be due to a shortage of lorry drivers or other staff owing to Covid-19 isolation requirements and may be a consequence of Brexit. Who knows? I’ll just say that there’s been hot weather in Ireland, where the Covid-19 pandemic is also happening but there are no reports of shortages of fresh food here. I’m very much looking forward to having a nice salad with my dinner this evening.

Anyway, I suppose that’s enough rambling. At some point I’ll have to open up my email box to see what horrors lurk therein. Still can’t be worse than the fridge I opened last week. Can it?

## Early Season Cricket

Posted in Cricket with tags , , on April 10, 2021 by telescoper

It’s Day 3 of Yorkshire versus Glamorgan at Headingley in the first round of this season’s County Championship matches.

Or it was because there won’t be any further play today owing to the inclement weather….

Glamorgan are actually doing well at 161 for 4 in their second innings after bowling out Yorkshire for 193 to establish a first innings lead of 137. That’s very good considering that they were 29 for 4 at one point. Currently 298 ahead with six wickets remaining, can they force a result tomorrow?

UPDATE: Glamorgan batted on for an hour on Sunday morning so both Clarke and Root could get hundreds, eventually declaring on 241-4 a leady of 378. Clarke and Root came together with the score on 29-4 so that was an unbroken partnership of 212 for the 5th wicket. Despite a wobble here and there, Yorkshire batted out the day and eventually a draw was agreed with their score on 223 for 4.

## On the Coronavirus and the Cricket

Posted in Covid-19, Cricket with tags , , on July 29, 2020 by telescoper

Yesterday the UK Government reported that there were 119 Covid-19 related deaths in the United Kingdom:

In other news, it was also announced yesterday that Stuart Broad and I have now taken 500 Test wickets between us…

## The people who do things and what they do

Posted in Art, Cricket, Football, Opera, Television with tags , on July 19, 2020 by telescoper

It’s a tough lesson to learn in life that the people you admire or idolize for their contribution in a particular arena (whether that be sport, art, science or something else) turn out to be people you can’t stand in terms of their character or political views.

You have to separate, for example, having a high regard for Ian Botham’s cricketing prowess from having a high regard for his personal character. In fact I can think of few sportspeople whose company I’d enjoy socially.

The same goes in many other spheres. Richard Feynman was a truly great physicist but I’ve never bought into the personality cult surrounding him. In fact I doubt I would have liked him very much at all if we’d ever met in person. They say you should never meet your heroes. They’re right.

Another example is Richard Wagner, a brilliant composer but really horrible man, who brings us to this clip from the end of Twilight of the Gods (the last episode of Series 7 of Inspector Morse, first broadcast in 1993).

I won’t spoil the plot if you haven’t seen it but it involves a famous opera singer, Gladys Probert, who visits Oxford to perform and receive an honorary degree. On the way to the ceremony she is shot, but was she the intended victim?

Opera-loving Morse is a huge admirer of Gladys Probert but in the course of his investigation he uncovers some unpleasant truths about her private life. He solves the crime but the case leaves him dispirited.

Here is the ending. John Thaw is Inspector Morse and Kevin Whateley is Detective Sergeant Lewis.

## Cricket Lovely Cricket!

Posted in Cricket, Music with tags , , on July 8, 2020 by telescoper

How great it is to see the return of Test Match cricket to England and the comforting familiarity it brings of sitting around not watching any play because of the pouring rain and Stygian gloom.

There may not have been much cricket at Southampton today (lovely or otherwise) but I couldn’t resist sharing this bit of West Indies cricketing nostalgia in calypso form, vintage 1950, by Lord Beginner..

## Predictive Blogging

Posted in Covid-19, Cricket, Opera, Politics, The Universe and Stuff with tags , on May 27, 2020 by telescoper

News has emerged that on 14th April 2020 Dominic Cummings doctored an old blog post to make it look like he had predicted a coronavirus outbreak. Given the indisputable fact that Mr Cummings is a career liar this should not in itself come as a surprise. What might surprise a few people is that this episode reveals that this self-styled genius is must in reality be rather stupid if he thought he could get away with hiding such a blatant attempt at self-promotion. Still, the truth obviously no longer matters in post-Brexit Britain so he probably won’t face any serious consequences.

I, of course would, never add things to old blog posts to make myself look clever.

I would, however, like to point out just a few of the various uncannily accurate predictions I have made in the course of my almost twelve years of blogging.

My love of Italian opera makes me regret even more that the UK will be be leaving the European Union in 2020.

And in this account of the May 2015 England versus New Zealand Test Match at Lord’s you will find:

… it was still quite gloomy and dark. My mood was sombre, thinking about Donald Trump’s forthcoming victory in the 2016 United States Presidential Elections.

My prescience is not only limited to politics, however. In my 2013 post about the Queen’s Birthday Honours List you will read:

The name that stood out for me in this year’s list is Professor Jim Hough, who gets an OBE. Jim is Professor of Experimental Physics at the University of Glasgow, and his speciality is in the detection of gravitational waves. Gravitational waves haven’t actually been detected yet, of course, but the experimental techniques designed to find them have increased their sensitivity by many orders of magnitude in recent years, Jim having played a large part in those improvements. I imagine he will be absolutely thrilled in February 2016, when gravitational waves are finally detected.

You see now that Niels Bohr wasn’t quite right when he said “It is difficult to make predictions, especially about the future”. Sometimes it’s the past that’s hardest to predict.

## R.I.P. Bob Willis (1949-2019)

Posted in Cricket with tags , on December 4, 2019 by telescoper

Just back from a lecture to find news of the death at the age of 70 of former England fast bowler and captain Bob Willis. I’m sure I’m not the only person who is now reminiscing about that day at Headingley in 1981 when Australia needed only 130 to win and, as Wisden later described it, “Willis ran in to bowl as if the Devil were at his heels”. As Christopher Martin-Jenkins wrote:

With his Test career in doubt for the umpteenth time, Willis, of the big heart and vicious bounce, gave it everything he knew. Brushing aside the cost of regular no-balls, he bowled at fierce pace to a shorter length and a straighter line than in the first innings. And suddenly Australia’s foundation crumbled…

R.I.P. Bob Willis (1949-2019)