Ideal Gas Law causes the air pressure of a football to decrease in colder weather, a physics lesson the NFL inadvertently learned/taught last year when it punished the New England Patriots after the league claimed two staffers tampered with the game balls in the AFC championship game.

The franchise countered that the deflation of the balls was an act of nature, not subterfuge.

You were no doubt bored with the back-and-forth a long time ago.

It'll be far colder in the second meeting this season between the Seahawks and Vikings. (AP) More

Forget deflate-gate, Seattle is visiting Minnesota on Sunday afternoon and the weather forecast calls for temperatures to hover around zero. If so, it could rank as one of the 10 coldest games in NFL history. The wind chill is expected to hit between minus-15 and minus-20.

This could deliver the mother of all psi level drops.

The NFL requires balls to be inflated between 12.5 and 13.5 pounds per square inch. The NFL's own internal investigation said footballs on the day of the AFC championship game in Foxborough, with temperatures in the low 50s, could naturally reach 11.32 psi. The lowest-recorded Pats football was either 10.5 or 10.9 depending on the measuring gauge used.

So how low should the air pressure go Sunday in the brutal chill of Minneapolis?

Try about 9.0 psi. Maybe even into the 8s.

"Ignoring the wind chill (meaning the following is a conservative estimate, meaning the wind chill could make the on-field ball pressure even lower), the on-field ball pressure will be about 9 psig (assuming it was pressurized to 12.5 psig at 70F and measured on-field at 0F)," Dr. Michael Naughton, the chair of the physics department at Boston College wrote to Yahoo Sports.

That's a low-pressure ball.

Last spring the league ruled two Patriots staffers, John Jastremski and Jim McNally, purposely deflated the footballs. It fined the franchise $1 million, docked it a draft pick and issued a four-game suspension to star quarterback Tom Brady.

Brady beat the suspension in federal court and hasn't missed a game.

While whatever the air pressure is Sunday has nothing to do with whether the Patriots did or did not tamper with the footballs last year, it poses a complication to a league that has taken significant interest in inflation levels after deflate-gate. That includes selectively testing footballs pre- and postgame at halftime to guard against tampering and to acquire data.

Prior to last January, the NFL never paid too much attention to psi levels. Refs would set the balls and forget about it. Teams and players, however, often paid attention. In December 2014, a little more than a month before seflategate, Minnesota hosted Carolina in 13-degree temperatures. Television cameras caught sideline attendants using heaters to warm up the balls. The NFL warned both teams of the rule violation.

"You can't do anything with the footballs in terms of anything artificial, whether you're heating them up, whether it's a regular game ball or kicking ball," NFL vice president of officiating Dean Blandino told the NFL Network.

"So that was noticed during the game," Blandino continued. "Both teams were made aware of it during the game and we will certainly remind the clubs as we get into more cold weather games that you can't do anything with the football in terms of heating them up with those sideline heaters."

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