It&#8217;s a pretty safe bet that you won&#8217;t hear any football coach utter this phrase: &#8220;That&#8217;s the way the prolate spheroid bounces!&#8221;</p><p>Yet, that&#8217;s one reason why football is so unpredictable and fun.</p><p>A football&#8217;s shape is called a prolate spheroid, which is a spheroid with a polar diameter longer than its equatorial diameter. While a true prolate spheroid has rounded edges, a football has pointed ends. Again, however, this makes the game exciting.</p><p>Unlike a baseball, basketball or soccer ball, a football can have some crazy bounces. That&#8217;s because of its shape.</p><p>Michael Kruger, a physics professor at UMKC, proposed an experiment where you would drop a soccer ball.</p><p>&#8220;Put a ruler against a point on a soccer ball where it&#8217;s going to hit (the ground),&#8221; Kruger said. &#8220;If the ruler is parallel to the floor, the ball will bounce straight back up. No matter how you put the sphere (soccer ball), this is the same.&#8221;</p><p>The ruler becomes the tangent, which is a line sharing a common point with a curve or surface and being the closest linear approximation of the curve or surface at that point.</p><p>Next up, Kruger used a football. It also can bounce straight up, but it has to land on its long axis. More often than not, the ball will bounce away from a person who drops it.</p><p>&#8220;The ruler no longer is parallel to the floor and that will not bounce back up,&#8221; Kruger said.</p><p>Timothy Gay notes in his book <em>Football Physics: The Science of the Game</em> that the shape of the football also can affect the spin.</p><p>&#8220;The football&#8217;s prolate shape also means that when it hits the ground with one of its points, a relatively large torque can be exerted on the ball&#8217;s center of mass,&#8221; Gay wrote. &#8220;In contrast, most of the force exerted by the ground on a soccer ball is the vertical force, which passes through the ball&#8217;s center.</p><p>&#8220;This means it has no leverage on the ball, so it can&#8217;t change its spin. The rotation of a football can change dramatically if one of its points is the first part to make contact with the ground. This change in the ball&#8217;s tumbling motion can add significantly to the punt returner&#8217;s difficulties, but it can also complicate the job of the offensive players trying to down the ball.&#8221;</p><p><strong><span class="subhead">History of a football</span></strong></p><p><em>Popular Mechanics</em> researched the history of the football in competition, and found that the first game in 1869 used a round ball like a soccer ball.</p><p>In 1874, a rugby-type ball was used in a contest between McGill University and Harvard University. The magazine noted that the new ball looked like a watermelon. It stayed roughly that way until 1912.</p><p>&#8220;That year, a new set of rules for college football transformed the game ball from the watermelon-shaped ball to an oversize version of today&#8217;s modern football,&#8221; the magazine wrote. &#8220;The pros soon followed. The ball now weighed 14 to 15 ounces, its long axis was set between 28 and 28 1/2 inches and its short axis (around the middle) between 22 1/2 and 23 inches.&#8230;</p><p>&#8220;In 1935, the NFL shortened the ball&#8217;s short axis to between 21 1/4 and 21 1/2 inches. The ball&#8217;s length was shortened that year to between 11 and 11 1/4 inches, and the amount of air that it could hold was set at 12.5 to 13.5 psi. Its long axis of 28 to 28 1/2 inches, however, did not change. These dimensions remain today, as does the ball&#8217;s shape, which has been called a &#8216;prolate spheroid&#8217; since 1890.&#8221;