# The big physics of sport roundup!

2016’s ‘summer of sport’ began in style with international football, with the UEFA European Championship and the Copa America Centenario kicking off in June. There’s been top notch tennis at Wimbledon, record-breaking golf tournaments, hard-fought cricket tests and we’re halfway through the baseball season. And that’s not mentioning all the other major sporting events this summer.

But can physics help athletes?

Of course! Let’s take a look at seven sporting events and the basic physics involved, a great article to get a grounding in sports science, with examples including the 100m sprint, the pole vault  and the dynamics of cycling. Starting with the pole vault: at its simplest, the athlete runs as fast as possible to create kinetic energy, and then needs to convert that, via the pole, into potential energy. The athlete’s technique then determines how effective that is, hopefully directing their body over the bar at the maximum height.  Or how about the simplicity of the shot put; the great strength and technique required of the athlete boils down to launching the shot put as fast as possible, and at the right angle (about 42°). Not so easy with a 7kg metal ball. Find out a bit more over at Physics Education or check out a focus issue on the Physics of Sport published by the European Journal of Physics.

What of golf? It’s not the most prestigious competition (that honour typically belongs to the 100m sprint), but it is being reintroduced into a particular event for the first time since 1904 – an absence of 112 years. It’s also a nice game of physics: many aspects of the game are based on elementary principles. Playing the sport is of course a great deal more difficult, with great control and technique required as well as a thorough understanding of the effect of differing conditions a must for any player. And so we have the physics of golf. From the double-pendulum swing to the aerodynamics of the ball – and ever wondered about those golf ball dimples? Hint: they make the ball go further. A lot further.

I should mention golf wasn’t the only game reintroduced, with rugby coming back after a 92 year gap. It might not be as obvious, but physics plays an important role here too – check out this book on the topic if you’re interested.

Correlation between the size of the sports field  for the different sports and the associated ballʼs maximum range. Baptiste Darbois Texier et al 2014 New J. Phys. 16 033039, CC-BY 3.0.

Sportsmen and women will be running around a wide variety of pitches and fields throughout the summer, but have you ever wondered why each ball sport has a different size playing area? Fear not, as ‘On the size of sports fields‘ – an article from CNRS researchers in France – drives to the heart of the question. It turns out that the size of each area is effectively determined by the range of the ball – and all studied open-field sports roughly follow the same principles, from golf down to tabletennis. Even badminton fits – it simply has a much higher drag coefficient than other sports. What isn’t clear is how modernisation has changed these sports. As sports equipment has improved, range has gone up significantly, increasing the pace of games like tennis and cricket. If these games were invented today, would the play area be bigger, or would societies’ ache for high-action games keep the play areas lower?

Cycling has seen a meteoric rise in popularity in recent years. Admittedly, that is perhaps a slight overstatement; but it remains a hugely popular activity both casually and professionally. The physics of it, is according to this article in Physics Education, a “complex mixture of aerodynamics, physiology, mechanics, and heuristics”. However, using simple models you can obtain a clear understanding of the key concepts: how aerodynamic drag affects the overall energy use and maximum speed of a cyclist. To maintain a given speed, a cyclist must provide additional energy equal to the energy lost through drag, and in order to accelerate they must exceed it. This makes it obvious that cyclists need as low a drag coefficient as possible. Aerodynamic drag increases quickly at high speeds, giving cyclists fast-diminishing returns on their effort. This is why you have the ‘race position’ and lycra-clad athletes; all to reduce the drag coefficient by minimising the amount of displaced air and its friction moving around the body. It also explains why cyclists sit as close behind one another as possible: the lead cyclist has to expend significantly more energy to overcome the buffer of air in front of them, whereas the following cyclist is already in a flow of air – similar to the ‘slipstream’ in motor racing. This makes team cycling tactical, such that this extra workload is shared. Learn more about the physics in Physics Education: Exploring the aerodynamic drag of a moving cyclist.

The different separation points on the two sides of a spinning football lead to a deflected airstream. Iwan Griffiths et al 2005 Meas. Sci. Technol. 16 2056. Copyright 2005 IOP Publishing Ltd. All rights reserved.

With a new season days away and World Cup qualifying soon after, football teams around the world are looking to improve their game. Perhaps physics can help?

Again, yes, of course! Iceland became renowned in the recent UEFA European Championship, not only for their unprecedented progress in the tournament, but also for their long throw-ins. Iceland’s throws led directly to goals in several of their games, helping to eliminate England in the quarter finals. Maybe they took their inspiration from our Physics World team who reported on a new book which found the perfect angle to release the ball from the side-line. Regardless, managers this year will surely look at whether the long throw might work for them. Many teams also suffered from a lot of missed shots and opportunities; a standard lament of every football fan. I suggest players might improve their shots-on-target by learning how spin affects the lift co-efficients of the ball. Better yet, use physics to understand how to swerve the ball effectively. No amount of physics will turn you into the next Ronaldo, but it’ll surely help.

Best of the rest

There is a lot of sports science related research out there. Some more abstract than others, such as how exactly do we measure the speed of a serve in tennis? Or a pitch in baseball? As fans we love these statistics, so take a minute to understand how it works, and why a single radar gun might get the speed of the ball wrong.

Schematic diagram showing a cricket ball viewed from above and illustrating the principle of conventional swing with a new ball. Copyright IOP Publishing, All Rights Reserved.

Finally, I wanted to write a bit about my favourite sport, cricket. Whether you love it or don’t understand it, there is some fascinating (and complex) physics going on with the ball. The biggest conundrum is swing bowling, the subject of a recent Physica Scripta paper. What exactly causes the ball to swing left or right, and why does this seem to vary so much with conditions and bowlers? Much of the exact understanding is still a mystery, but the spin of the ball, the weather conditions and how the ball moves through the air have a major impact. Typically a fast bowler puts spin on the ball, and this allows it to swing by more than 20cm, and even vary the length of the delivery by 3 m. The amount of swing is also affected by the roughness of the ball (hence why cricketers will shine one side) and by the weather: under certain conditions the Magnus effect (responsible for this movement) can reverse – causing reverse swing.

Not a fast bowler? No problem, you’ll want to know how spin affects a delivery for a slow bowler. Typically a slow bowler is aiming to turn the ball off the pitch in order to bamboozle the batsman. However, spin bowling has many subtleties; is it off spin, top spin, leg spin? How about the flight? A spin bowler has a large number of possible deliveries, each giving the batsman something different to deal with. Altering the spin not only changes the turn of the ball, but its sideways movement in the air and its length. A minor change from the bowler can lure a batsman into an edge, or overestimating the pitch of the ball potentially providing an easy catch. So, enhance your spin bowling with the help of Physica Scripta.

So as you settle down and watch the worlds finest athletes this summer, give a though to the physics behind those motions and what they are doing to achieve the very best.

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