Science of NFL Football: Geometric Shapes - Spheres, Ellipses & Prolate Spheroids

Air Date: 09/24/2010
Source:
NBC Learn
Creator:
Lester Holt
Air/Publish Date:
09/24/2010
Event Date:
09/24/2010
Resource Type:
Science Explainer
Copyright:
NBCUniversal Media, LLC.
Copyright Date:
2010
Clip Length:
00:04:10

NBC's Lester Holt explores the prolate spheroid, the three-dimensional shape of a football, and how it helps an NFL quarterback throw a hard, accurate pass. "Science of NFL Football" is a 10-part video series funded by the National Science Foundation and produced in partnership with the National Football League.

Science of NFL Football: Geometric Shapes - Spheres, Ellipses & Prolate Spheroids

LESTER HOLT, reporting:

Whether throwing a screen or launching a bomb, NFL quarterbacks are spin doctors, firing fast spirals that cut through the air with pinpoint accuracy.

JOEY HARRINGTON (Former NFL Quarterback): The shape of the football is unique and allows you to be able to throw at the distances that you can.

HOLT: Former NFL quarterback Joey Harrington says the secret to throwing the perfect spiral starts with his fingertips.

HARRINGTON: I like it this way because it helps me gets a little more rotation on it. It helps me to get a little more spin.

TONY SCHMITZ (University of Florida): The spiral is what tends to keep it going along the path that the quarterback would like.

HOLT: Professor Tony Schmitz is a mechanical and aerospace engineer at the University of Florida, and coach of the Newberry High School football team. Around campus, he's known as the “Pigskin Professor”.

SCHMITZ: My enjoyment for football started when I was very young.

HOLT: Schmitz says the key to throwing a tight spiral comes from a football's unique shape, which is different from the ball used in most other sports like tennis, baseball, and basketball.

SCHMITZ: Most sports use a round ball or a sphere because it's symmetric. No matter where I hit it, no matter where it bounces, it will have the same response.

HOLT: While spherical balls come from the two dimensional shape of a circle, footballs are formed from a two dimensional shape called an ellipse. An ellipse can then be divided by its two axes: its long, or major axis, and its minor axis.

SCHMITZ: From the two-dimensional shape of an ellipse for a football, if we were to rotate that about its long axis from one end to the other, we end up with a prolate spheroid.

HOLT: A prolate spheroid. This clumsy word may explain some of the mad dashes seen after a fumble. But what makes a football unpredictable on the ground is also what makes it travel through the air so smoothly and accurately.

ANTONIO FREEMAN (Former NFL Wide Receiver): It is very surprising how accurate they are but I do realize how much work goes into to being that accurate.

HOLT: Unlike a spherical ball, the prolate spheroid shape actually helps the football to spiral, through something called the gyroscopic effect, which helps maintain its control and trajectory by its continual spin.

SCHMITZ: We can think about the gyroscopic effect of this--of the spiral as being, um, a stiffening effect on its path. It tends to keep it on that path.

HOLT: A spiraling football is also effective at moving through the air because it reduces the amount of drag, or air friction, against the ball. As the football spirals, the air on the surface of the ball is broken up, allowing for less drag and a smoother trajectory.

SCHMITZ: That rotating motion tends to break up that boundary layer between the fixed air and the football surface, which reduces drag.

HOLT: But if a football is thrown a little off, it begins to wobble. A lame duck, or wobbly pass, encounters more drag and does not benefit from the gyroscopic stiffening of its trajectory.

HARRINGTON: If I've got a ball that is kind of, you know, wobbling like this, it creates more surface area for the wind to hit it.

HOLT: So the tighter the quarterback's spiral, the less air resistance on the ball, allowing it to travel farther.

SCHMITZ: Without the spiral it would be very difficult to keep the football on a path.

FREEMAN: It becomes a thing of perfection and-- and quarterbacks love to be perfectionists.

HOLT: Perfection that only a prolate spheroid can provide.

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