How to rig a football to deflate (Update)

UPDATE Jan. 27, 2015:  Physicist spells out a way to make footballs “shrivel to completely flat after cooling.”


The New England Patriots could have legally rigged footballs to wind up underinflated.

Patriots head coach Bill Bellichick spelled out much of this scenario in a news conference much of the media apparently failed to understand.

He said vigorous rubbing to break in the balls raised the internal temperature. Then the air was adjusted (by the NFL refs, he implied), to the minimum, per the team’s request. Taking the ball into the cold outside would then automatically drop the air pressure below the legal minimum.

Bellichick argued it was all just accidental.

But could his confusing speech have been deliberately vague to cover up further but actually legal steps?

Heat inside, deflate, take outside

1. Heat it. (Hair dryer, warm in a sauna, running under hot water in a shower or hot tub.) Air pressure inside increases.
2. Release air to legal minimum (12.5 pounds per square inch).
3. Let refs check the ball. Seems OK.
4. Take outside in cold weather. Air inside chills and air pressure drops.

Nefarious but totally legal.

UPDATE: Boston University physics professor Martin Schmaltz spells out how a ball acclimated to a heated room could read 12.5 psi then show a dramatic pressure drop after being exposed to cold.

Replace dry air inside with steam, etc.

1. Remove all air. Pump up ball in environment saturated with steam or water vapor (like a locker room).
2. Follow steps 1 to 4 above.
5. Because of the cold, water vapor/steam inside CONDENSES, and air pressure inside DROPS EVEN MORE.

Bellichek was able to explain a pound on underinflation.

Perhaps the steamy explanation could account for the full two pounds.

This also explains why nothing unusual inadvertently happened to the footballs used by the Indianapolis Colts.

UPDATE: Physics professor Schmaltz agrees (to a degree). He emailed:

you are right.

although air at full saturation and 12.5 PSI pressure only holds about a factor of 2 less moisture than air at one atmosphere (assuming the same temperature). so the total amount of water is not that much, about 0.3 worth.

However, if you combine both effects, heat and water vapor, you can win big. As an extreme example, if you were to fill the balls with pure steam (at > 212F) to 12.5 PSI then the balls would shrivel to completely flat after cooling down just a little. of course, the ref might notice that something’s up 😉 but even a modest increase in temperature allows much higher levels of partial pressure due to water vapor.

cheers -m

UPDATE: USA Today shares same theory, quotes another physics professor:

Chang Kee Jung, a football fan and physics professor at The State University of New York at Stony Brook, chuckled when the theory was explained. But he agreed it’s possible — not only because of the temperature change, but other effects from the steam in the sauna.

“If you put it in the moisture with the hot air, then what happens is that some of the air — which is moist water — it could condense and then it could even more rapidly lose pressure,” Jung said. “They may consider it not illegal, but if they actually did it, does that really pass the moral test?”

A third wrinkle (new): Chill footballs on the sidelines

If the Patriots chilled balls in a cooler before using, they would have deflated even more — without releasing any air.

Once the media picks up the proper explanations, talk will deflate about punishing the Patriots, because if there was cheating, it didn’t violate the rules.

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