Search results for: “art”

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: 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: 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
Sharks Swimming Sideways
Like many sharks, the great hammerhead shark is negatively buoyant, meaning that, absent other forces, it would sink in water. To compensate, sharks generate lift with their pectoral (side) fins to offset their weight. Their dorsal (top) fin is used to generate the horizontal forces needed for control and turning. However, both captive and wild great hammerhead sharks tend to swim rolled partway onto their sides. The reason for this unusual behavior is hydrodynamic – it is more efficient for the shark. Unlike other species, the great hammerhead has a dorsal fin that is longer than its pectoral fins. By tipping sideways, the shark effectively creates a larger lifting span and is able to induce less drag than when it swims upright. Models show that swimming on their sides requires ~8% less energy than swimming upright! (Image credit: N. Payne et al., source)
August 4, 2016
Hagfish Escape Mechanisms
The hagfish is an eel-like creature that has not changed much in the past 300 million years in part because the hagfish is very good at escaping would-be predators. When attacked, the hagfish excretes mucins that combine with seawater to form slime. This gel-like viscoelastic fluid forms quickly and has some handy properties. For example, when stretched, the slime becomes extremely viscous. Many fish feed using a suction method, in which they thrust their jaws forward and enlarge their mouths to suck water and prey inside. This strong unidirectional flow stretches the slime, which thickens it and clogs the fish’s gills. Suddenly, the fish is much more concerned with being unable to breathe, allowing the hagfish to flee.
Being surrounded by all that slime could smother the hagfish, too, if it were not for another clever feature of the slime. When sheared, hagfish slime collapses, losing its viscosity. The hagfish actually ties itself in a knot to create this shear and slide the slime right off. (Image credit: V. Zintzen et al.; L. Böni et al., source)
August 1, 2016
The Evaporation of Ouzo
Ouzo is an aperitif made up of ethanol (alcohol), water, and anise oil. This three-part, or ternary, mixture undergoes an intriguing evaporation process thanks to the characteristics of its components. An ouzo drop’s evaporation can be divided into four phases, each shown above. Initially, the drop is well-mixed and transparent (upper left).
Since ethanol is the most volatile of ouzo’s components, it evaporates the most quickly. As the ethanol evaporates, the drop becomes oversaturated with oil (upper right). Oil droplets form, giving the ouzo a milky appearance. At the same time, the ethanol evaporating causes gradients in surface tension, which drive a vigorous Marangoni flow inside the drop.
Eventually, the ethanol finishes evaporating and the oil drops collect in a ring around the outside of the drop (lower left). Slowly, the water inside the drop evaporates. Eventually, a tiny microdroplet of water is left to dissolve in the anise oil (lower right). (Image and research credit: H. Tan et al., source; via Inkfish)
July 29, 2016
Crisscrossing Clouds
This natural-color satellite image shows crisscrossing cloud patterns off coastal Africa. These distinctive lines in the sky are gravity waves, and they form when air masses get displaced upward by terrain or other conditions. In this case, dry air cooled overnight on land before moving out over the ocean. That displaced warm, humid air above the water and forced it upward, where it eventually cooled and condensed into clouds. Gravity created the ripple-like waves; as the moist air cooled, gravity again pulled it downward – leaving behind a clear sky. Once the humid air sank, the dry air pushed it up again, creating another line of clouds and continuing the cycle. (Image credit: NASA; via NASA Earth Observatory)
July 28, 2016

More posts