Why? The Science of Athletics

268 WHY?-THE SCIENCE OF ATHLETICS Relationship of Speed and Spring In dealing with the pole vault I have explained the relationship of speed in the approach run to success in jumping, but, before going on to that again, it should be made quite clear what one means by the statement that the true angle of jumping is one of 45 degrees. Af first sight this may well suggest that orie is going to jump far too high. In point of fact, 45 degrees is only the angle at the instant when the body immediately enters upon the path of its parabolic flight-curve, and is steadily acted upon by the force of gravity, which rapidly destroys the energy existing at the start and becomes nil,. at the highest point of the trajectory. If the earth did not attract a body to itself, the jumper would go on in a straight line for ever ; but it is this attraction which causes the body's flight to follow a curved line. During the first half or two-thirds of the curve the attraction of the earth is a retardation, but during the latter portion it acts as ai). accelerating force. The distance a man can clear depends also upon the velocity of projection, govern~d by the amount of impulse generated. To make this matter more clear, let us assume that the jumper weighs 140 lbs., that he jumps 22 ft., and approaches the take-off three times at varying speeds of 40 yards in 5 secs., 40 yards in 6 secs., and 40 yards in 7 secs. Those speeds represent velocities. of 24, 20 and 17· 14 feet per second respectively, and, to clear 22 ft . in the jump, the athlete's impulse must generate an initial velocity of 26·5 ft . per sec. It will be seen, there– fore, that this gives an increase of 2 · 5 ft. per sec., on the first speed, 6· 5 ft. per sec. on the second speed, and g· 34 ft. per sec . on the third speed. To find the impulse generated, the formula is : / P=m(u-v) m being the mass, viz. 140 lbs. u and v, the first anC:l second velocities respectively.