FYFD

Tag: olympics

  • Featured Video Play Icon

    London 2012: Archery Physics

    Archery is one of the oldest Olympic sports, but the physics involved are remarkably complex. Even looking only at the flight of the arrow, the problem is hardly simple. The heavy point of the arrow makes it front-heavy, and the fletches on the back of the arrow provide additional surface area on which air can act. This means that the center of mass of the arrow–where gravity acts–is further forward than the center of pressure–where aerodynamic forces act.  This results in the aerodynamic forces helping to stabilize the flight of the arrow.  To see why this is important, try throwing a dart fletching first!

    When an arrow is fired from a bow, as in the high speed video above, the sudden impetus of force from the bowstring causes the arrow to flex and vibrate as it is fired. The aerodynamic forces generated by the fletches straighten the arrow’s flight, helping it reach the intended target accurately.  Some fletching is designed to make the arrow spin; this can further improve accuracy but comes at the cost of speed since some of the arrow’s initial kinetic energy must be converted to rotation.  For more, check out Archery Report, which features some great articles on the physics of archery and even has CFD comparing arrow tips. Mark Leach also has some great information on tuning a bow, which, if done properly, allows one to accurately shoot unfletched arrows.

    FYFD is celebrating the Olympics by looking at the fluid dynamics of sports. Check out our previous posts on how the Olympic torch works and what makes a pool fast.

  • London 2012: Swimming Pool Physics

    London 2012: Swimming Pool Physics

    The era of the LZR suit may be over in swimming, but technology is still making an impact when it comes to making swimmers faster. One thing you’ll often hear from commentators is how the London Aquatic Center boasts one of the world’s fastest pools. When swimmers compete, they have to contend with all the turbulence created in the pool by eight people trying to direct as much water behind them as possible as quickly as possible. Like ripples spreading on a pond, these waves travel, reflect, and interfere, ultimately disrupting the swimmers and causing extra drag. In a fast pool, engineers have made adjustments to reduce the impact of these waves on swimmers. Firstly, the pool is 3 meters deep, meaning that vertical disruptions are mostly damped out before they reach the bottom, so any wave reflected off the bottom of the pool will be extremely weak. Along the sides and ends of the pool, a special trough captures surface waves, preventing them from reflecting back out into the pool. The lane lines are also designed to soak up wave energy so that it does not propagate as much between lanes. When waves hit the lines, their links spin, dissipating some of the wave’s energy.

    Despite these advances, the outermost lanes–those against the walls–are not used in competition. This helps to equalize the turbulence between lanes. Whether there is any fluid mechanical advantage to being in a particular lane is debatable. The outer lanes have the advantage of only one competitor’s wake to contend with, but they isolate the swimmer so he or she cannot see their competition as well. In the inner lanes, you’ll sometimes see swimmers try to swim close to the lane line if their competition is ahead of them, the idea being that they may be able to draft on their competitor’s bow wave to reduce drag. Generally speaking, the lane positions are determined by seeding going into the event, where the faster swimmers are given the innermost lanes. This is why it’s rare to see gold medals coming from the outermost lanes. For more, check out NBC’s video on designing fast pools (US only, unfortunately). (Photo credits: Associated Press, Reuters, Geoff Caddick)

  • The Olympic Torch

    [original media no longer available]

    Today marks the beginning of the 2012 Olympic Games in London. In the opening ceremony, the Olympic flame will complete its journey from Olympia to London, having been carried by some 8,000 torch bearers. Modern Olympic torches are expected to withstand wind, rain, snow, and human error to keep the flame alive and are specially designed and tested for these conditions. Each individual torch is fueled by a mixture of propane and butane stored as a pressurized liquid. The liquid fuel travels through a series of evaporation coils around the burner before combustion. Each torch carries sufficient fuel to burn about fourteen minutes. In addition to computer simulation, the 2012 Olympic torch design was tested in BMW’s Environmental Wind Tunnel to ensure a visible, stable flame for orientations within 45 degrees of vertical in conditions ranging from -5 degrees to 40 degrees Celsius, rain, snow, 35 mph winds, and 50 mph wind gusts. For more on the current torch and previous designs, see How Stuff Works, E&T, and the BBC.

    FYFD is celebrating the Olympics by featuring the role of fluid dynamics in sports starting Monday. If you have any burning questions, feel free to ask or email!