As Europe worries about the risks of deflation on the global economy, American football fans wonder about the ramifications of deflation on their beloved sport—and how a potentially deflated win might impact one team’s push to the Super Bowl. Meanwhile, we’re left wondering about the physics of a ball’s deflation.
By now you’ve probably heard. Despite their 45-7 AFC championship win against the Indianapolis Colts on Sunday, the New England Patriots are under pressure to explain why 11 of the 12 game balls in the match appear to have been improperly pressurized. As the home team in the game, the Patriots supplied the game balls and are now facing some awkward inquiries. While there are still a lot of questions about the incident—whether the deflating was unintentional or not, and who on the team might be responsible—there’s a more fundamental one to ponder: What sort of advantages can be had from a deflated football?
In Which We Ask a Physicist Soft Ball Questions
One thing that happens if a ball’s pressure is slightly lowered, says Timothy Gay, a physicist (and football enthusiast) at the University of Nebraska-Lincoln, is improved accuracy of a kick. Why? Because there’s “more contact area,” he says, “between your foot and the ball. Because the ball is more indentable.”
However, there’s also an inherent tradeoff. While accuracy may be improved, power is reduced. A deflated ball simply doesn’t travel as far even if the kicker kicks with his usual amount of force. That’s because the kicker is spending a little more energy in deforming the ball with his foot and a little less energy launching it away.
As Gay puts it: “The enhanced compression of the deflated ball lowers the force the foot delivers to it over the range of its travel before the ball loses contact with the foot. This lower force imparts lower kinetic energy to the ball.”
(For more on the physics of kicking a football—and how both Newton’s second law of motion [force equals mass times acceleration]* and the idea of impulse [force times the amount of time pressure is applied] apply—see video below.)
But What About Handling an Underinflated Ball? Get a Grip.
“They were having real problems with rain in the AFC championship, and if the ball is scrunchier—that’s a technical physics term, by the way—you can hold it more easily,” Gay says.
So if a team was worried about fumbling, deflating might be a way to help players get a better grip.
More Questions to Tackle
With the physics of a deflated ball under our belt, we’re left with more non-science questions. Will the scandal deflate the enthusiasm of New England Patriot’s fans? Does Bill Belichick, the team’s coach, have a hand pump secreted away in his trademark sweatshirt? Or is it all a product of tight end Rob Gronkowski’s post-touchdown spikes? We’ll need a little more evidence to make sense of this gridiron shrinkage.
*You might think that because a deflated ball weighs less than an inflated one, that might kick up its acceleration according to Newton’s second law of motion. But in this case, the change in mass is extremely negligible compared to the effects from the deformability of the ball.
By: Roxanne Palmer