Tag: olympics

Rio 2016: Badminton
Badminton is unusual among racquet sports because it does not use a sphere as its projectile. Instead players hit a shuttlecock, traditionally made from a cork ball and a skirt of goose feathers. Despite its unusual shape, the shuttlecock reaches some of the fastest speeds in sports – over 330 kph (200 mph)! The shuttlecock’s high-drag form quickly slows shots down but also gives the game very different trajectories compared to other racquet sports.
It’s likely that, if you’ve played badminton yourself, you’ve played with a shuttlecock that has a plastic skirt rather than a feathered one. These synthetic shuttlecocks are cheaper and more durable, but they also have different drag characteristics than their feathered cousins. At low speeds, synthetic shuttlecocks have more drag than feathered ones, but at high speeds, the opposite is true. This is because the plastic skirt deforms more easily than the feathers, causing a synthetic shuttlecock’s skirt to collapse into a shape with less drag. (Video credit: Science Friday; research credit: F. Alam et al.)
Join us throughout the Rio Olympics for more fluid dynamics in sports. If you love FYFD, please help support the site!
August 18, 2016
Rio 2016: Sailing and Rule 42
If you watch some of the sailing in Rio, you may hear commentators mention sailors being penalized for breaking Rule 42. Broadly speaking, Rule 42 says that sailors can’t use their body to propel the boat. While it seems like a little rocking couldn’t make much difference, it turns out events have these rules for good reason.
One way to break Rule 42 is to perform sail flicking, demonstrated in the animation above. The sailor uses his or her body weight to roll the boat slightly, which causes the sail to flick. Aerodynamically speaking, we’d call this motion heaving. On the flexible sail, this unsteady motion decreases drag, allowing the boat to go faster. Done with the right frequency and amplitude, sail flicking actually makes the sail’s drag become negative, thereby creating thrust!
The bottom image shows a visualization of the wake of a normal sail (left) and a sail being flicked (right). Both sails shed vortices in the downstream direction, but the flicked sail has much stronger vortices, indicated by the darker colors. In addition to giving a sailor an illegal boost, sail flicking creates more difficult, turbulent conditions for any competitors downstream, so it’s restricted in many (but not all) sailing events. (Image credits: AP Photos; Reuters; National Solo, source; research and flow diagram credit: R. Schutt and C. Williamson, pdf)
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August 17, 2016
Rio 2016: Long Jump
Long jump, like many track and field events, is affected by fluid dynamics in subtle ways. Both wind speed and altitude can modify a jumper’s performance – first, by changing the maximum speed they reach in their sprint, and second, through aerodynamic drag while in flight. Air resistance accounts for roughly 10% of a sprinter’s energy expenditure. A slight tailwind gives an athlete a minor boost in speed that can translate into a more significant increase in jump distance. On the other hand, though, a headwind of the same magnitude has an even stronger negative effect on performance.
The other factor, altitude, comes into play through air density. The official Olympic record for the long jump was set by Bob Beamon in the 1968 Mexico City Games. The high altitude of Mexico City results in an air density that’s only 75% of that at sea level. That’s tougher on athletes in terms of oxygen levels, but it’s a big reduction in the overall drag they face, resulting in both a higher sprinting speed and less aerial drag. This is part of why Beamon’s jump stood as a world record for well over 20 years! (Image credits: AP Photo; AFP/GettyImages; Reuters)
Previously: Can dimpled shoes help runners?; the unusual aerodynamics of the javelin; the physics of the discus
Join us throughout the Rio Olympics for more fluid dynamics in sports. If you love FYFD, please help support the site!
August 16, 2016
Rio 2016: Synchro Swimming and Water Polo
Both synchronized swimming and water polo require competitors to hold themselves stable above the water’s surface without touching the pool’s bottom. One of the basic techniques for doing so in both sports is known as the eggbeater kick, shown above. The eggbeater kick is very similar to the motion for the breaststroke’s kick, but it’s performed upright and with alternating leg motions, sweeping a clockwise circle with the left leg and a counterclockwise one with the right.
A swimmer typically stays afloat due to a buoyant force equal to the weight of the volume of water the swimmer displaces. Rising further out the water means reducing the buoyant force, so the swimmer must generate other forces to counter their weight. The eggbeater kick does this two ways. First, as the swimmer sweeps their foot around, it acts like a hydrofoil, generating lift that holds the swimmer up. Second, other parts of the kick cycle force water downward, which, by Newton’s third law, pushes the swimmer up.
Keeping a wide stance and sweeping the legs alternately allows the athlete to balance the horizontal forces their motions create while keeping the upward forces generated relatively constant. This gives them a stable, arms-free platform that’s a foundation for everything else their sport requires. (Image credits: GettyImages; The Studio WLV, source)
Previously: How buoyancy helps swimmers
Join us throughout the Rio Olympics for more fluid dynamics in sports. If you love FYFD, please help support the site!
August 15, 2016
Rio 2016: Track Cycling
Track cycling is a sport where speed is everything. As much as 90% of the resistance a rider has to overcome is aerodynamic drag. To minimize drag, riders wear form-fitting one-piece skinsuits and wear special, streamlined helmets. They have aerodynamic bikes (unique left-side-drive ones, if you’re the Team USA women) and ride with their arms close together and thrust in front of them to minimize the frontal area they expose.
Even the tactics of racing rely heavily on aerodynamics. In events like team pursuit cyclists stay extremely close to the wheel of the rider ahead of them in order to remain in that rider’s slipstream and experience less drag. When switching off the position of lead rider, cyclists use the curvature of the track to help them move to the back of the paceline quickly to minimize the time spent outside of their teammate’s draft. (Image credits: GettyImages via the Guardian and the IOC, source)
Previously: Cycling’s aero equipment helps them beat the clock; the effect of cyclists being followed by a motorbike or car
Join us throughout the Rio Olympics for more fluid dynamics in sports. If you love FYFD, please help support the site!
August 12, 2016
Rio 2016: Table Tennis
Many sports use spherical balls, but the small size and weight of a table tennis ball makes it the one where aerodynamics have the strongest effect. Spin also plays a big role in the game by creating asymmetry in the flow around the ball.
Consider a table tennis ball with topspin, meaning that its upper surface is rolling in the direction of travel. That means that air flowing over the top of the ball is moving in the opposite direction as the ball’s surface. This will tend to make the flow separate from the ball at its widest point.
On the other side, the ball’s surface is spinning in the same direction as the air flow. This helps hold the air to the surface so that it follows the curve of the ball longer and doesn’t detach until well after the ball’s widest point. As a result of both these effects, air flowing around the ball experiences a net upward force, which in turn pushes the table tennis ball downward. This is known as the Magnus effect, and it plays a significant role in many sports. (Image credits: GettyImages; AFP)
Previously: The Magnus effect and the reverse Magnus effect in soccer; curveballs and knuckleballs in baseball
Join us throughout the Rio Olympics for more fluid dynamics in sports. If you love FYFD, please help support the site!
August 11, 2016
Rio 2016: Whitewater Sports
The whitewater rapids of canoe slalom have their origins in mountain streams. Today the sport’s Olympic venues are artificial rivers, specially designed to provide world-class rapids whatever the geography of the host city. Rio’s course, like London’s, is reconfigurable; its features are controlled by the placement of Lego-like plastic blocks.
A key part of the course’s design process was building a small-scale physical model of the course. To maintain the dynamics of the rapids at a smaller physical scale, engineers used a concept called similitude. Surface waves like rapids are a function of the flow’s inertia and the effects of gravity, a ratio that’s captured in the dimensionless Froude number. To match the small-scale model to the real flow, engineers scaled the features of the real course down such that the Froude number stayed the same between the model and the full-scale course. As seen in the animations above, this meant that the model had the same general flow features as the final course, letting engineers and designers test and fine-tune features before construction. Learn more about the model and its construction in these two videos. (Image credits: kayaker – Getty Images; model comparisons – J. Pollert, source)
Previously: Physics of rowing; why that octopus kite looks so real
Join us throughout the Rio Olympics for more fluid dynamics in sports. If you love FYFD, please help support the site!
August 10, 2016
Rio 2016: Rugby

The sport of rugby returns to the Olympics in Rio this year. Rugby’s ball is somewhat similar in size and shape to an American football, but it is a little wider and more rounded. Aerodynamically, this means that the rugby ball has more drag, but it is also more stable in flight, allowing players to pass and kick accurately, with or without a spiral.
As seen in the flow visualizations above, air travels up and around the ball before separating on the far side. The more the ball is tilted, the larger this separated region is and the greater the drag. At the same time, though, that tilt provides lift on the ball. The ideal orientation is the one with the largest ratio of lift force and drag force. For a rugby ball, this occurs at about 40 degrees.(Image credits: Planet Rugby; A. Vance et al.)
Previously: The aerodynamics of the American football
Join us throughout the Rio Olympics for more fluid dynamics in sports. If you love FYFD, please help support the site!
August 9, 2016
Rio 2016: Swimming
Strange as it seems, elite swimmers are faster when swimming underwater than they are at the surface. So much so, in fact, that they’re restricted to being underwater only 15 m after a dive or turn. To see just how stark a difference this makes, check out this crazy video. (I know, right?!)
To understand how this is possible, it helps to look at the three types of drag a swimmer experiences: pressure drag, skin friction, and wave drag. Pressure drag is probably the most familiar; it’s the drag that comes from the swimmer’s shape and how the fluid moves around it. Skin friction is the drag that comes from viscous friction between the swimmer and the water. The final type, wave drag, comes from the energy expended to create waves at the surface of the water. As you might expect, energy that goes into splashing is energy that isn’t going into propulsion.
When swimming at the surface, swimmers experience a lot of wave drag. At least one experiment showed that wave drag accounted for most of a surface swimmer’s drag. In contrast, at a depth of more than 0.5 m, a swimmer’s wave drag is virtually negligible. The submersion does come at the cost of higher skin friction (since more of the swimmer is in contact with the water), but there is also more opportunity for useful propulsion since both sides of a kick can move water (and not air.) Bonus read for those interested in more: Is the fish kick the fastest stroke yet? (Image credits: AP; B. Esposito)
Previously: what makes a pool fast?
Join us throughout the Rio Olympics for more fluid dynamics in sports. If you love FYFD, please help support the site!
August 8, 2016
Rio 2016: Cycling
Today marks the official start of the 2016 Summer Olympics in Rio. Here at FYFD we’ll be celebrating by taking a look at how fluid dynamics affects Olympic sports. You can check out our previous series on the London Olympics here. Since this weekend features the men’s and women’s cycling road races, we’ll get started with cycling!
In road cycling, equipment and race strategy are all built around aerodynamic efficiency. It’s understood that following a car or motorbike gives a cyclist an unfair advantage, and officials can be quick to punish infractions. What the rules don’t account for, though, is the advantage a cyclist gets when they’re followed by a motorbike (or car). These vehicles are significantly larger than a cyclist, and when they are trailing a cyclist, they have a significant upstream effect. Essentially the higher pressure traveling ahead of the motorbike will counter the low pressure region immediately behind the cyclist. The result is that the cyclist, despite being in front, experiences less drag than they would if the motorbike weren’t there.
The difference isn’t tiny either: if a motorbike follows a rider at a distance of 0.5 m for just 1 km, the rider saves more than 2 seconds. When events can be won or lost by fractions of a second, those gains are significant. (Image credits: DCMS; B. Blocken et al., GettyImages, Reuters; research credit: B. Blocken et al.; submitted by Marc A.)
August 5, 2016