Sports physicist says temperature could have caused football deflation

Never before has PSI been talked about this much.

The now overly scrutinized deflate-gate controversy isn't just an issue of the integrity of the game, it is a matter of physics as well. Dr. John Eric Goff, a renowned sports physicist who is a professor at Lynchburg College, wants to set the record straight about some of the recent calculations going around about the New England Patriots and how the under-inflated footballs got that way in last Sunday's AFC championship game.

Goff said there is a very real possibility that a ball can deflate during the course of a game, something that anyone who has played a sport on a schoolyard knows all too well. But other factors come into play, including how much the temperature drops, that can make the pounds per square inch (PSI) drop.

Suppose the referees in their pregame routine checked the game balls in a locker room at 70 degrees Fahrenheit. When the Patriots and Indianapolis Colts kicked off, the temperature was 51 degrees Fahrenheit. According to Goff, a ball at the league minimum of 12.5 PSI would then be at about 11.5 PSI “because as temperature drops, pressure in the ball drops.”

This would continue and if the temperature dropped another 10 degrees to 41 degrees Fahrenheit as the game went on, the pressure of the ball would be about 11 PSI.

Or, this could explain Tom Brady's deflated footballs.

A pressure drop of 1 PSI, or even 1.5 PSI might be detected by an experienced player, but the effect would be hard to notice by mere mortals not used to handling footballs all the time," Goff said. "The ability to squeeze the ball better, even if it's just a slight improvement, can only help a quarterback using a ball made slick by rain.  Despite lower pressure due to a temperature drop, the ball's weight remains the same because no air leaves the ball as it cools.  If the ball is retested at a later time at the same temperature at which the ref tested it prior to the game, the ball should be back to its old pressure because it would have warmed from game temperatures to testing temperatures.  Again, no air would have left the ball." 

Any NFL player will tell you that a deflated football is easier to catch. As the temperature gets colder, the ball gets harder. During a cold gameday, players will often rub a football after a play, they say, to unleash the natural oils in the football. This makes it easier to catch.

Goff, who is the author of the interesting Gold Medal Physics book, also notes that when and where the balls were tested before the games matters. If done indoors, as is NFL protocol, then the deflation might not be a surprise. While he cautions that he can't speculate as to what happened, certain factors can impact the PSI measurement.

So it might be the weather, or it might just be some flaws in the mechanisms and environment for testing the balls before the game, but it doesn't rule out someone manually letting the air out.

Where deflate-gate gets sticky is that retested balls were found to be at lower pressures," Goff said. "As long as the retesting was done in the same environmental conditions as the referee's initial pre-game test, the most probable way for the pressure to be lower, assuming no leaks due to tears, is for air to have been let out. 

The point is that temperature changes make it possible to have a ball flying around in a game that is below the allowable range, but players are not likely to notice much difference.  If pregame and post-game tests are done in the same environment, and different pressures are measured and there are no leaks, the balls can't contain the same amount of air.”

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Kristian R. Dyer writes for Metro New York and is a contributor to Yahoo! Sports. Follow him on Twitter @KristianRDyer