![]() ![]() Such overexertion is a common problem for baseball pitchers, for example. In some ball sports, the difficulty of transferring elastic energy efficiently from the arm to the ball can cause much of the kinetic energy of the throw to stay within the body, potentially leading to injury. The enhancement factor remained around 2.5, however, when the whole projectile was soft. The best improvements were for soft layers of up to about 30% of the total cylinder height-where the efficiency could be improved threefold. The optimal performance occurs when the duration of the platform’s upward acceleration is approximately equal to the natural oscillation period of the vibrating soft layer, so that the most energy can be transferred from platform to projectile. The researchers found that a soft layer can always improve the ejection efficiency relative to a rigid cylinder. The transient dark regions in the gel layer are caused by changes in optical properties due to comp. (The gel thickness determines the platform oscillation frequency at which each projectile reaches its maximum height.) Projectiles with various thicknesses of gel (transparent layer) launched in a single oscillation cycle from a platform moving at a frequency of 76 Hz. The best improvement in efficiency of energy transfer occurs for thinner gel layers. The transient dark regions in the gel layer are caused by changes in optical properties due to compression, which provides a view of the gel’s internal oscillations. Projectiles with various thicknesses of gel (transparent layer) launched in a single oscillation cycle from a platform moving at a frequency of 76 Hz. They determined the efficiency of energy transfer by measuring the heights to which the projectiles rose.į. The rigid portion of each cylinder was made of hard plastic, and the researchers added a squishy layer of gelatin hydrogel of various thicknesses (from about 6 mm to the full height) to the bottom of some projectiles. ![]() The researchers used a spring-loaded platform to deliver upward thrust to cylindrical projectiles 12 mm wide and 15 mm tall. The team has now run similar experiments on rigid objects with an added elastic component as a way of studying throwing efficiency in a simplified system. A drop of water launched upward from an oscillating platform can gain up to 2.5 times the kinetic energy of a rigid ball with identical mass when the platform vibrates at about one-third the frequency of the drop’s intrinsic oscillations (see also Focus: Superpropulsion of Liquid Drops). They have previously shown that timing can be crucial to efficient propulsion when the projectile is deformable and elastic. These movements are not driven purely by muscle power but also involve the release of elastic energy stored in the tendons, as in a catapult.įranck Celestini and Christophe Raufaste of the University of Côte d’Azur, France, and their colleagues have now looked at how that energy transfer might be improved in a simple model system in which a projectile is launched from an upward-moving platform. Throwing involves a complex chain of events that couple the movements of the limbs, skeleton, muscles, and tendons to give the projectile kinetic energy. The results could be used to design better projectiles in sports and could lead to shoe designs that enhance energy transfer during walking and running. Their experiments show that, compared with a rigid projectile, one that includes some soft, springy material can receive up to 3 times more kinetic energy when launched upward. A team of scientists now shows how throwing efficiency could be improved by engineering the elasticity of the projectile. Throwing is as central to some sports today as it once was for hunting and warfare. The projectiles are shown before release (top), during deformation as the platform rises (middle), and at their maximum heights (bottom). A lineup of plastic projectiles is propelled upward by an accelerating platform, with each cylinder having a different thicknesses of a gel layer at its base. ![]()
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