Measurement in sport – the long and the short of itInternational sporting events require more than well-trained athletes. Behind the scenes, a wide range of scientific and technological wizardry are needed to ensure accurate measurements.
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Key textAustralians are famous – or infamous – for being sports-mad. We play it, we watch it, we love it. But have you ever wondered about the purpose of so much activity? The long and the short of it is...well, just that, the long and the short of it! When people play sport, they need some way of comparing performances: whether on a netball court or a sprint track, measures are needed to separate the winners from the losers.How measurement is used in sport
Measurement is an essential element of all sports in two ways. First, measurements are taken to determine the outcome of an event, such as which runner was fastest or which pole-vaulter jumped highest. Second, measurements are used to communicate the agreed rules and regulations of a particular sport. It would be unfair, for example, to claim a world record in the 50 metres freestyle event if the swimming pool is a few centimetres short of the required length (Box 1: Olympic track and pool facilities). Units of measurement
The starting point for any measurement is the unit of measurement. For it to be useful, everyone must agree on which unit to use and what it means. In contrast to the precision of today, units of measurement in the past were often quite imprecise. For example, one cubit was the distance from a person's fingertip to their elbow. An acre was originally the area of land that a team of two oxen could plough in one day. These units were not always comparable: people vary in size, and the work-rate of oxen depends on a whole range of factors, including what they ate for breakfast. To improve accuracy of measurement, people soon realised that units must be based on agreed standards. These days, most units of measurement used in Australia are those of the International System of Units. In this system, seven of the units have been selected to be base units. Larger or smaller multiples are obtained by combining the unit with an appropriate prefix, for example kilo (which means a thousand) is combined with metre to form kilometre (which means a thousand metres). The base units most often encountered in sport are the metre, the second and the kilogram. Some units are derived from these base units by combining two or more of them (eg, metre per second for speed or velocity). In certain cases these derived units are given a special name, such as newton for the units of force. Of course, some sports have quite arbitrary units of measurement. The unit in soccer, for example, is a goal – soccer players the world over agree that the team scoring the most goals wins the game. Measuring devices
With the pressures of international competition comes a demand for increasingly accurate and fail-safe measuring devices. Science and technology play an important role in developing more sophisticated measuring devices for use in major sporting events. For example, to decide who is the fastest human on Earth, we need to measure distance and time accurately. Timing devices used in running events have undergone enormous changes. In the 1912 Olympic Games, hand-operated mechanical stopwatches were used with an accuracy of 0.2 of a second. By 1932, the accuracy of stopwatches had improved to 0.1 of a second (Box 2: Perfect timing: Timing devices and reaction time). Measuring for improved performance
Science can explain the way we use the forces of nature in various sports. Friction, air resistance and gravity are all forces that are important in sport. Understanding and measuring these forces can help athletes improve their technique and also lead to improvements in the design of equipment (Box 3: Physics in sport: Forces on an athlete). In addition, manufacturers of sporting equipment, clothing and playing surfaces constantly rely on measurements to improve their products in the quest for the next world record, or just to provide safe and reliable facilities and equipment. For example, rackets and balls have undergone many changes in design, materials and construction methods. Such innovations have increased the speed of ball games such as tennis and squash (Box 4: Rackets and balls). Getting your measure
Anywhere you look in sport, people are measuring – the distance of a javelin-throw, the time of a race, the number of goals, the dimensions of a pool. Sometimes the difference between winning and losing is just a hundredth of a second – a difference that can only be determined by a computerised timing device. Maybe we are too fanatical about it – but, then again, there are few things more frustrating than an inconclusive result.
Sydney International Aquatic Centre The Aquatic Centre will be the venue for swimming, diving, water polo and synchronised swimming during the Games. Swimming champion Kieren Perkins described this $150 million facility as 'the biggest and the best' he had ever seen. It is fully covered and consists of four pools: a competition pool, a utility and diving pool, a training pool and a free-form leisure pool. The dimensions of the competition pool (50 x 25 metres) must comply with standards set down in the handbook of the international body for swimming which specifies details such as pool length, width and depth. Usually, some variation is permitted, provided it falls within a certain range (this is called the allowed tolerance). The competition pool must be 50.0 metres long with a tolerance of +0.03 metres and -0.00 metres. (This means that the pool can be up to 3 centimetres longer than 50 metres but not even a millimetre shorter.) A qualified surveyor must certify that all measurements are within the regulations. Olympic Stadium The Olympic Stadium will seat up to 110,000 spectators and will be used for various events including track and field athletics and the opening ceremony. A standard athletics track has an inside running distance of 400 metres. Most tracks have an 85 metres straight on each side, with curves at either end with a radius of 36.41 metres. There are usually eight lanes, each 1.22-1.25 metres wide. Tracks must have two independent measurements made of their length, using either a steel tape or a laser-based surveying instrument. The two measurements may not differ from each other by more than the allowed tolerances or the track will not be certified for national and international competition. Related site
Hand-held stopwatches have become more accurate, but they depend on human judgement and reactions. This places an absolute limit on accuracy – times will be uncertain by at least 0.2 of a second. Over a 100 metres foot-race this is equal to an error of 2 metres. Such inaccuracy presents considerable difficulties. For example, in the 1960 Olympic Games in Rome, Australia's John Devitt and America's Lance Larson finished neck-and-neck in the final of the 100 metres freestyle swimming event. Two of the three first-place judges had Devitt as the winner, but two of the three second-place judges had Devitt second. Among the timekeepers there was no doubt: all three on Devitt's lane gave him 55.2 seconds, while the timekeepers on Larson's lane gave him 55.0, 55.1 and 55.1 seconds – all faster than Devitt. But all six measurements were within 0.2 of a second of each other; thus, they did little to help decide the winner. On the basis of the decisions by the first-place judges, the race was awarded to Devitt and the official time for both was recorded as 55.2 seconds. John Devitt received the gold medal. In 1964 an electronic quartz timing system was used for the first time in international events, thereby improving timing accuracy to 0.01 of a second. The computerised timing systems used in events today have increased the accuracy to 0.001 of a second, which is 10 times the accuracy required under the rules. Judging very close running races remained a problem until photo-finish video cameras were used at the finish line. (Originally, film-based cameras were used, but this meant that athletes and spectators had to wait until the film was developed before they knew the result.) The introduction of the vertical line-scanning video system in 1991 totally removed human judgement and reactions from the timing and judging of world class running events. The starter's pistol is linked to a transducer, which detects the sound made when the starter pulls the trigger. The transducer is connected to a timing computer, which starts to count immediately it receives the signal. Connected into this system is a high quality video camera located at the finish line. This produces the official time and a video image of the athletes as each one passes the finish line. The video camera scans a thin line aligned with the finish line up to 2000 times per second. The video image of each athlete as they actually cross the line is shown superimposed with a grid that records the time for each competitor. This system allows judges to declare the result more quickly and more accurately. (Two parallel infra-red beams also located at the finish line are directly linked to display boards within the stadium. They provide the audience with an instant but unofficial time for the race.) Reaction time Reaction time is the time that elapses between the moment a stimulus is detected by the brain and the moment a response starts. Tests have confirmed that nobody can react in less than 0.110 of a second. Sprinters need excellent reactions to ensure that they leave the blocks as quickly as possible after hearing the gun. Australia's Cathy Freeman, a world-class athlete, had a reaction time of 0.223 seconds in the 1995 World Championships women's 400 metres final. A device within each starting block records the interval between the gun firing and the first athlete leaving the blocks. A false start is declared if this interval is less than 0.110 of a second, since the runner must have decided to go before hearing the gun. Related site
Sir Isaac Newton first proposed this idea in the 1600s. He said that for every force (action) there is an equal force (reaction), which acts in the opposite direction. Action-reaction pairs of forces associated with an athlete are due to gravity, friction with the ground and air resistance. Ground reaction force and shock absorbency Runners move across a surface by a series of long strides. Each time a foot lands, the ground exerts a force on it, which is then distributed (absorbed) by the runner's body. Considerable damage can occur to the runner's ankles and knees unless the force is reduced. Elastic playing surfaces can absorb some of the force; so can running shoes with elastic foam layers in the soles. An elastic playing surface such as grass feels springy to run on and produces fewer injuries than more rigid surfaces such as concrete. But the time spent rebounding is higher on a springy surface, slowing the runner down. The best surface for athletics is one that is absorbent enough to limit injuries but firm enough to give athletes the best chance of achieving optimum results. Frictional forces The force of friction applies when you move any two surfaces against each other. Friction works in a direction opposite to the direction of motion. The size of the frictional force depends on the force pushing the two surfaces together and their roughness. Playing surfaces and the soles of running shoes must provide sufficient friction to ensure that runners do not slip. However, too much friction between surfaces and shoes can lead to ankle and knee injuries. Measuring friction The friction between two surfaces before they move is called static friction. Once the two surfaces are on the move it is easier to keep them moving and the value of the frictional force becomes less. This force is known as sliding friction. The friction between surfaces can be compared by calculating the coefficient of friction. This is the frictional force in newtons divided by the weight of the object in newtons. It can be calculated for both sliding and static friction. Running tracks used for international competitions must have a minimum coefficient of sliding friction of 0.5 under wet conditions (when the surface is most slippery). This standard has been set to help prevent athletes from slipping unduly. Physics in field athletics Field athletics consists of four throwing events (discus, javelin, shot and hammer) and four jumping events (high jump, pole vault, long jump and triple jump). All throws and jumps can be divided into four stages: the approach, the launch, the flight and the impact. The success of a throw or a jump will be affected by several factors. At the launch stage, the speed, angle and height of take-off will all influence the outcome. During the flight stage other factors come into play such as the shape of the object, the speed and direction of the wind, and the force of gravity. An athlete strives to perfect a throwing technique by giving the object the greatest possible speed at the moment of release. Other factors such as the angle of release and the height of release also affect the distance travelled by the object. Jumping Another factor to consider in jumping events is the athlete's centre of mass (or centre of gravity). This is the point around which the total mass of the athlete is evenly distributed. Its exact position varies from person to person depending on build, and it shifts as you move. The best jumping technique will be one that allows the jumper to keep their centre of mass as low as is consistent with clearing the bar. This allows the athlete to achieve a higher jump using less energy, because more energy is needed to raise the centre of mass higher. In high jumping, a technique known as the Fosbury flop, introduced in the 1960s, led to a dramatic increase in the world record. It involves leaping head-first at the bar and twisting in mid-air, so that the front of the body faces upwards. The technique shifts the athlete's centre of mass to the underside of the body as it passes over the high jump bar, thereby keeping it as low as possible. Related sites
On impact with a racket or the ground, a ball flattens or compresses, regaining its original shape as it pushes against the surface and rebounds. The property of a ball that causes it to regain its original shape is called its elasticity. Energy changes on impact A falling ball has kinetic energy (energy of motion). On impact, some of the kinetic energy is stored in the ball as elastic potential energy. As the ball returns to its original shape and starts to rebound, the elastic potential energy is converted back into kinetic energy. (Some of the original kinetic energy is lost on impact, being converted into heat and sound. This means that the rebound height is always less than the starting height.) The greater a ball's elasticity, the faster it will return to its original shape and the farther it will rebound when it is hit or kicked. In tennis, changes in the design of tennis balls have increased their elasticity, significantly speeding up the game – the ball travels faster when hit, and the tennis players must travel faster to get near it. Squash balls are made with different elasticities. They are colour-coded as fast or slow balls. Rackets Modern squash and tennis rackets have enabled players to increase ball speed. The technology comes from aerospace research and new manufacturing techniques. Tennis racket frames were first made of solid wood. A stronger racket was produced when the frame was made of laminated wood – thin layers of wood steamed, glued and pressed together. Later, metal rackets were made of steel, titanium, magnesium and aluminium. The strength of the metal meant that frames became narrower and lighter and could travel faster through the air. Today, no top-class player uses wooden rackets, and very few use metal ones. Instead, the frames are made of composite materials. These consist of fibres – such as carbon fibre, glass fibre, boron, Kevlar and ceramics – bonded together using a resin. These composite materials are stronger, lighter and stiffer than wood. A stiff racket frame absorbs less of the ball's energy, thereby increasing the power available to the player. Ball speed Tennis has become a faster game as a result of new designs in rackets and balls. Top players can serve at up to 220 kilometres per hour, making the judgement of line-ball decisions extremely difficult. Line judges are now able to rely on an electronic eye to determine if a ball is out. Related site
Australasian Science June 2000, pages 34-36 Fast times at Stadium Australia...maybe? (by Peter Blanchonette, Mark Stewart and Ian Blanchonette)
October 1999, pages 28-30 How high can Emma fly? (by Peter Blanchonette and Mark Stewart) Discusses the physics of pole vaulting.
The Helix June/July 2000, pages 10-15 The science behind the Olympics (by David Harris)
June/July 1998, pages 28-29 Extreme sports – taking science to the extreme (by Rebecca Scott)
April/May 1997, page 4 Timing a second
August 1991, pages 22-23 Ski physics (by John Cashion)
New Scientist 26 January 2002, pages 30-33 Zeros into heroes (by Wilson da Silva) Describes the kinds of data that are collected at the Australian Institute of Sport.
12 September 1998, page 13 Slugging it out (by Ian Anderson) Describes the three 'sweet spots' on a baseball bat.
12 September 1998, page 65 The last word – brim swim Explains why swimming is more difficult when a pool is not filled to the correct level.
1 August 1998, pages 36-39 Swim like a fish (by Daniel Drollette) Olympic swimming coach Gennadi Touretski uses his knowledge of engineering, biomechanics, biochemistry, fluid mechanics and sports physiology to train his athletes.
21 March 1998, page 6 Big is better (by Mick Hamer) Sprocket scientists have given cyclists a speed boost.
6 September 1997, pages 66-67 Game, set and match (by Jonathan Knight) Power servers in tennis use a dead spot on their racket.
Physicsweb September 2000 Physics, technology and the Olympics (by Steve Haake) Discusses the effects of technology on the performance of athletes in sports.
Velocity March 2007 The virtual world of swim analysis Explores the new space-age pool for swimmers.
Sportscience (The Exploratorium, USA) Looks at the science behind baseball,
skateboarding,
surfing
and cycling.
Also has activities and a question and answer section.
The science of sport (Discovery Channel, USA)
Provides the science behind a number of sporting activities including mountain biking and track and field.
The Sports Factor (ABC Radio National) Transcripts from the ABC radio program, The Sports Factor.
How pole vaulting works (How Stuff Works, USA)
Covers the physics of pole vaulting.
The science of sport (British Broadcasting Corporation, UK)
Looks into the science behind different aspects of sport including timekeeping.
International System of Units (abbreviated to SI). SI is based on the seven units shown in the table; all other units are derived from them. These units are represented by reproducible, agreed physical standards which allow accurate measurements to be made anywhere in the world. Australia's physical standards of measurement are maintained by the National Measurement Laboratory, which is a National Facility within CSIRO.
The seven SI base units of measurementnewton. The SI unit of force. One newton gives an acceleration of 1 metre per second per second to a mass of 1 kilogram. The weight you feel when you hold an average size apple in your hand is about one newton (mass is about 0.1 kilogram and gravitational acceleration of about 10 metres per second per second). It is named after Sir Isaac Newton. transducer. A device that converts one form of energy into another. For example, an electric jug converts electrical energy into heat energy. A transducer connected to a starter's pistol converts sound energy into electrical energy.
External sites are not endorsed by the Australian Academy of Science. Posted November 1998. The Australian Foundation for Science is also a supporter of Nova.
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