Pigskin Physics: What's the Big Deal About Deflated Footballs?

Making an NFL Football

Jan. 21, 201501:43

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The New England Patriots' victory over the Indianapolis Colts in Sunday's AFC Championship game was marred by allegations that the Patriots used deflated footballs. Late Tuesday night, those suspicions were bolstered by Chris Mortensen of ESPN.com, who cited NFL sources who said that 11 of the 12 game balls used by the Patriots during the game were under-inflated by 2 pounds per square inch (psi). The allegations have not been confirmed by NBC News.

But if the balls were deflated, what is the big deal?

"The higher the pressure, the harder and more firm the football becomes," Mike Eads, physics professor at Northern Illinois University, told NBC News. Conversely,the lower the pressure, the more "give" the ball has, potentially making it easier to catch in cold, slick weather. But lighter balls are also "more influenced by air resistance," he said, meaning they don't travel as far. Deflated balls can also make short field goals easier.

Making an NFL Football

Jan. 21, 201501:43

"Basically, a little bit of air removed from the ball makes it easier to kick accurately because you get more ball surface in contact with the toe," Timothy Gay, physics professor at the University of Nebraska, told NBC News. "The more air you remove the shorter the range because the ball behaves more like a mattress and less like a stiff spring, so that the kicker expends more energy deforming the ball and less giving it velocity."

In essence, balls deflated below the NFL-mandated 12.5 to 13.5 pounds per square inch could be easier to catch and kick short distances, but aren't great for long bombs.

Even if the balls were deflated, it's not clear the Patriots would be at fault. For those who remember the "ideal gas law" from high school chemistry, a drop in temperature can result in a drop in pressure. The same football that measures 12.5 psi at 68 degrees Fahrenheit, Eads said, would drop to 11.6 psi in 32 degree weather. During the game in Foxborough, Massachusetts, the temperature hovered in the 40s, reaching a high of 51 degrees Fahrenheit.

Regardless of what the NFL finds, the New England Patriots are headed to the Super Bowl XLIX to play the Seattle Seahawks. The championship hopes of the Indianapolis Colts remain deflated.