With 113 million viewers in the U.S. and 40 million more globally, the Super Bowl is North America’s most popular sports event. This year’s game on Sunday—with the added appeal of a high-profile romance—aims to draw a similar viewership. In Canada, last November’s Grey Cup final recorded a peak viewership of 3.7 million, witnessing the Montréal Alouettes’ triumph. The popularity of the two leagues is not comparable, nor are their rules.
Another distinction lies in the footballs used, which look alike but have specific characteristics on either side of the border that influence aerodynamics, that is, the air forces on the ball during flight. The ball’s design and features impact the magnitude of these forces. Football players might find it surprising, but throwing skills aren’t the sole factor. Several elements affect the ball’s aerodynamics, including its construction and inflation pressure. As a mechanical engineering professor at Québec’s École de technologie supérieure, I focus on experimental fluid dynamics, investigating fluid flow physics for various applications like aquatic vehicle propulsion and aerodynamics. Fluid dynamics covers a broad scope, impacting numerous facets of life, from heart blood flow and aircraft flight to Jupiter’s atmospheric swirls or the perfect football touchdown pass. The NFL and CFL share identical rules regarding ball dimensions.
They must measure between 11 and 11.25 inches in length, and be inflated to between 12.5 and 13.5 psi, resulting in a maximum circumference of 28 to 28.5 inches in length and 21 to 21.25 inches in width. These dimensions play a crucial role. A football functions like a gyroscope, meaning the faster it spins, the more stable its flight. Variations in dimensions can influence flight stability. A larger circumference implies more of the ball’s mass being farther from its center, leading to a higher moment of inertia—or resistance to rotation—meaning the same force results in a slower spin speed. While Canadian rules mandate two white stripes on the ball and laces, American rules don’t specify these.
These distinctions between Canadian and American balls can affect their drag. Drag is the resistance encountered by a moving object in a fluid; in this scenario, it’s primarily air resistance, also known as form or pressure drag. Consider a golf ball; its dimples encourage turbulence, allowing the airflow to adhere to the ball, reducing total drag, enabling it to travel further with the same force. A football’s laces and other significant surface alterations (like logos or valves) might similarly affect drag when combined with rotation. Exploring how NFL and CFL footballs differ in drag would be intriguing. To investigate, a wind tunnel—a controlled airflow tunnel experiment—could simulate air movement around the balls, which would be held in place, rotated, and exposed to airflow mirroring their flight speed. An aerodynamic force balance could measure drag differences between the two balls under identical conditions. Ideally, both balls would need identical dimensions to remove variability factors.
Smoke or particle image/tracking velocimetry could visualize air movement around the ball, using particles like helium-filled soap bubbles or oil droplets, filmed to assess airspeed at all ball-encompassing points. This would showcase airflow separation and recirculation areas and offer insights on aerodynamic force distribution around the ball. Various rotation and flight speeds could be assessed, considering possible flow instabilities that might modify air behavior around the ball. Such studies could determine which, NFL or CFL balls, performs better. Another drag type arises from air-surface friction, known as friction drag, largely determined by ball texture and speed. A rougher texture increases friction drag at any given speed, as does faster ball speed. Reducing form drag further lowers total drag, enabling faster and longer football field travel.
Weather conditions also influence football aerodynamics. Temperature extremes can modify ball size by altering inner air pressure. Likewise, cold makes the ball stiffer, and heat makes it softer. Temperature and humidity impact air’s physical properties, affecting its density and viscosity. Rainhead directly alters drag, indirectly affecting ball surface texture as perceived by air. However, this won’t be a concern during Las Vegas’s February 11 Super Bowl, as Allegiant Stadium is an indoor venue. This article was initially written in French.