How does physics help sport?

Physics is not only relevant to the “big questions” of where the universe came from and how it works – it has many real-life applications too.

Sport is just one of them, and, with the Games coming to London for July–September, physics is behind much of the summer’s action.

Right on time
Physics is used for precision timing of runners’ movements – from starting block to finishing line.

Modern starting blocks are integrated with a high-tech starting gun system – if its pressure sensors detect that an athlete has lifted his or her feet sooner than human beings can physically react – 0.1 seconds – they’re automatically pulled up for a false start.

At the other end of the track, the days of photo-finishes and closely examining which runner is a nose ahead at the finish line are long gone. Instead, RFID tags – similar to those used in retail stores’ security tags, but much more precise – are used to definitively tell which athlete crosses a line first, and how quickly. Some transponders are attached to runners’ shoes, others are stuck to their race number – the latter are thought to be more accurate as they detect when the torso, rather than a foot, crosses the finishing line.

Using the force
To excel at any sport, mere athleticism is not enough, and competitors need to develop good technique to run, swim or row faster than their opponents.

In rowing, hi-tech paddles are fitted with pressure sensors that are used to work out the forces on each part of the oar at different points during a stroke. Athletes can then review a graph of the force at different times during their training session with their coach,. This enables them to determine which aspects of their technique need to be worked on in order to give them the best chance of getting on the winners’ podium.

Material world
Runners, cyclists and swimmers experience a force pushing them in the opposite direction to which they’re travelling, caused by resistance of the air or water through which they’re moving.

Improvements in technique such as cyclists changing position can minimise this force by reducing cross-sectional area (to which it is proportional). Cyclists hugging their bodies tightly to the bike’s frame can reduce drag force by half. But careful design of materials can also make more fluid flow around an athlete’s body, rather than pushing against it.

Around 2009, swimmers began using full-body swimsuits with polyurethane panels. The tight suits squeezed swimmers into a smaller cross-sectional area as well as eliminating skin friction, allowing water to flow over the body more easily. Their introduction coincided with a spate of world records being broken.

Health and safety
Physics-based methods such as ultrasound are routinely used by physiotherapists to assist them in healing and monitoring sportspeople’s injuries.

High-frequency sound waves are used to create an image of, for example, a footballer’s knee. Because different tissues reflect those waves back at different intensities, physiotherapists can tell what type and depth of tissue they’re looking at.

They’re used diagnostically for problems such as fluid on the knee, or to spot tiny tears in tendons before they become major problems – preventing athletes having to suffer a long layoff while they recover.

A leg up
Prosthetic limbs have come a long way from the wooden legs associated with 16th-century pirates. While they were rigid crutches, modern prostheses are designed to emulate real limbs by storing and then releasing energy.

The rigidity of the carbon-fibre prostheses used by Oscar Pistorius, the best-known amputee runner, changes depending on where forces are applied – they remain stiff towards the knees but the parts that contact the ground are springy.

In fact, they’re so good that Pistorius was deemed by the International Association of Athletics Federations to have an unfair advantage over able-bodied runners until the decision was overturned by the International Court of Arbitration in Sport in 2008.

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