November 8, 2010
2 min read
Why the prolate spheroid is the shape for success
By The Editors
NBC Learn's "The Science of NFL Football" episode about geometric shapes explores the differences between spheres, ellipses and prolate spheroids, and their impact on the game. The unique shape of the football, for example, contributes the dynamic nature of the ball itself, which can be thrown long distances in a tight spiral or bounce unpredictably on the field of play.
Baseballs, basketballs and many other sports balls rely on a spherical, uniform design that makes them easy to shoot, throw and hit. A football, however, owes its two-dimensional origin to the ellipse rather than the circle, giving the pigskin its prolate spheroid shape, which has a polar axis that is greater than its equatorial diameter. Thanks to its elongated nature, a football will spiral when thrown properly. The spin creates a gyroscopic effect, stabilizing the flight of the ball through the air.
This shape makes the football more difficult throw than a spherical ball. But, as a prolate spheroid, a football experiences less drag as it cuts through the air, which explains why you can toss a football farther than a spherical ball such as a basketball or soccer ball that is roughly the same size and weight. When a football is thrown with a bit of a wobble, as opposed to a tight spiral, it will not travel as far, because it presents more surface area in the direction of flight resulting in a greater degree of air friction, also called drag.
Improving the ball's original design has not proved easy. The best football shape would consider both reduced drag and trajectory stabilization, according to Tony Schmitz, an associate professor in the University of Florida's Department of Mechanical and Aerospace Engineering. "Right now, we have the pebbled surface and spiral motion that reduce drag," he says. Any design that "increases these effects could give improved 'flight' performance, but good luck making a significant change." The toy company Hasbro did make some interesting alterations in its Nerf lineup—its Nerf Vortex football has a tail, for example, which improves the distance it travels when thrown. How such a ball would travel when kicked is entirely different issue, of course.
Aircraft, submarines and rockets share the basic design principles as footballs in that their shapes are elongated in an effort to reduce drag. These vehicles are self-powered, however, and must be able to change direction mid-flight, so they cannot use the spinning gyroscopic effect that makes a perfectly thrown spiral such a thing of beauty.
As far as identified flying objects go, however, prolate spheroids cannot match the distance of one class of geometric shape: A flying disc (Frisbee) or ring (Aerobie) not only have slim profiles that reduce drag and rotation that increase stability, but they also create lift, enabling them to carry quite far. On a football field, a well-thrown Aerobie can easily go from end zone to end zone.
As a seasoned expert in physics and engineering, particularly in the realm of aerodynamics and geometric shapes, I can confidently delve into the intriguing article that discusses the significance of the prolate spheroid shape in the context of football.
The prolate spheroid, as highlighted in the article, serves as the fundamental shape of a football. My expertise allows me to expound on the intricate physics behind this unique design. Unlike spherical balls used in sports like baseball and basketball, a football's prolate spheroid shape, with its polar axis greater than its equatorial diameter, contributes to its distinctive flight characteristics.
The article elucidates how the football's shape, derived from the ellipse, results in a dynamic and challenging projectile. When thrown properly, the football spirals due to the spin, creating a gyroscopic effect that stabilizes its flight. This property makes it more difficult to throw than a spherical ball. However, the prolate spheroid shape offers advantages, such as reduced drag as the ball moves through the air.
The concept of drag is crucial in understanding the aerodynamics involved. The elongated nature of the football minimizes drag compared to a spherical ball, allowing it to travel farther. The article explains that a well-thrown football with a tight spiral experiences less air friction or drag, contributing to its increased distance.
Tony Schmitz, an associate professor in the University of Florida's Department of Mechanical and Aerospace Engineering, is cited in the article. His insights into improving the football's design emphasize the delicate balance between reducing drag and stabilizing trajectory. The mention of the pebbled surface and spiral motion reducing drag highlights the meticulous engineering considerations involved in optimizing the football's flight performance.
Moreover, the article draws parallels between the design principles of footballs and other vehicles like aircraft, submarines, and rockets. These vehicles share the elongated shape to reduce drag during motion. However, it's noted that unlike footballs, these vehicles are self-powered and must be capable of changing direction mid-flight, precluding the use of the spinning gyroscopic effect employed by a perfectly thrown football.
A fascinating comparison is made with flying discs, such as Frisbees, and rings like the Aerobie, which boast slim profiles to reduce drag and rotation for stability. These objects can also generate lift, allowing them to cover substantial distances. In the context of a football field, a well-thrown Aerobie is described as capable of traversing from end zone to end zone.
In summary, the article provides a comprehensive exploration of the geometric shapes in sports, specifically focusing on the prolate spheroid shape of a football and its intricate aerodynamic properties. My in-depth knowledge allows me to affirm the credibility of the information presented and appreciate the nuanced physics at play in the world of sports projectiles.
