the vaulter fails to begin an attempt within this time, the vaulter is charged with a time foul and the attempt is a miss. Poles are manufactured with ratings corresponding to the vaulter's maximum weight. As a safety precaution, some organizations forbid use of poles rated below the vaulter's weight. The recommended weight roughly corresponds to a flex rating that is determined by the manufacturer by applying a standardized amount of stress (most commonly a weight) on the pole and measuring how much the center of the pole is displaced. Therefore, two poles rated at the same weight are not necessarily the same stiffness. Pole stiffness and length are important factors to a vaulter's performance. Therefore, it is not uncommon for an elite vaulter to carry as many as ten poles to a competition. The effective length of a pole can be changed by gripping the pole higher or lower in relation to the top of the pole. The left and right handgrips are typically a bit more than shoulder width apart. Poles are manufactured for people of all skill levels and body sizes, with lengths between and and a wide range of weight ratings. Each manufacturer determines the weight rating for the pole and the location of the maximum handhold band. Speed is an essential element to high jumps. The horizontal kinetic energy produced by the run is converted to vertical propulsion . Assuming no loss of energy , this means that . Technology Competitive pole vaulting began using solid ash poles. As the heights attained increased, bamboo poles gave way to tubular aluminum, which was tapered at each end. Today's pole vaulters benefit from poles produced by wrapping pre-cut sheets of fiberglass that contains resin around a metal pole mandrel, to produce a slightly curved pole that bends more easily under the compression caused by an athlete's take-off. The shape of the fiberglass sheets and the amount of fiberglass used is carefully planned to provide the desired length and stiffness of pole. Different fiber types, including carbon-fiber, are used to give poles specific characteristics intended to promote higher jumps. In recent years, carbon fiber has been added to the commonly used E-glass (E for initial electrical use) and S-glass (S for solid) materials to create a lighter pole. As in the high jump, the landing area was originally a heap of sawdust or sand where athletes landed on