The Fosbury Flop
Physics has greatly influenced the progress of most sports. There have been continual improvements in equipment for safety or performance as well as improvements in technique. The Fosbury Flop is a good example of physics helping improve the performances of the sport significantly. The Fosbury Flop is a technique used by athletes in High Jump and is named after Dick Fosbury who won gold in the 1968 Olympics held in Mexico. This is the most used technique in High Jump nowadays. The secret to the effectiveness of the Fosbury Flop lies in the center of mass of the athlete being located below the bar during the jump.
The Center of Mass(CoM) of a body is the average position of all its mass by taking into account how the mass is spread around the object. For instance, the center of mass of a rectangular piece of metal lies at the intersection of the diagonals. Similarly, the CoM of a disc lies at its center.
The CoM of a person standing normally is somewhere around the belly. But this shifts upwards if the person raises his arms. So the CoM of a person varies continuously throughout the day as he performs various tasks. But it is important to note that the CoM need not lie within the boundary of the body itself. The CoM of a boomerang lies outside the body as well as the doughnuts.(see Figure below)
The Fosbury Flop takes advantage of this. So during the jump, at the peak, the athlete’s body is shaped like an arc similar to that of a boomerang.
At this position, the center of mass of the athlete is located below the bar. You might be wondering how the center of mass falling below the bar helps improve the jump.
The answer is simple. Since the CoM is now at a lesser distance from the ground, lesser force is required by the athlete to lift his body. He thus expends lesser energy in a Fosbury Flop compared to a jump of same height using another technique.
To perform this jump, use a ‘J’ shaped run-up approaching the bar perpendicularly in the first three to five strides. The Flop style of high jump is characterized by (at least) the final four or five steps being run in a curve, allowing the athlete to lean into his or her turn, away from the bar. Unlike the traditional style of jumping, where the athlete jumps with his face/body facing the bar, he jumps the other way around with his back facing the bar. Additionally, on take-off the sudden move from inward lean to outwards produces a rotation of the jumper's body along the axis of the bar, aiding clearance.
Combined with the rotation around the jumper's vertical axis produced by the drive leg (think of an ice skater spinning round on the spot) the resulting body position on bar clearance is laid out supine(lying face upwards) with the body at ninety degrees to the bar with the head and shoulders crossing the bar before the trunk and legs. This gives the Flop its characteristic "backwards over the bar" appearance, with the athlete landing on the mat on his shoulders and back.
But it is important to note that the Fosbury flop was not a feasible technique back when the landing pits were filled with sand softened with wood shavings. Earlier, the straddle technique was a better option for the athletes taking into factor the high probability of being injured by utilizing the Fosbury Flop. Later on, when the landing pits were cushioned with nice thick foam, the flop became feasible. Another factor contributing to the popularity of the Flop among the athletes is the ease in learning the flop compared to the other techniques.
To sum up, the high jump competition, along with many other sports, is being exploited by physics!
Varun Seshadri, Team Technothlon ‘17