Bob CollinsAs much as we want to roll our eyes over the ongoing question of whether the New England Patriots intentionally deflated footballs in last Sunday’s AFC championship win over the Indianapolis Colts, it does grant our long-time wish: that we’d pay as much attention to academics as sports. In this case: science.
In a NewsCut post last week, we provided several explanations for why the pressure in a football could be reduced by the physics involved.
That brought a NewsCut first a day later: a professor of physics writing to correct the formula used for the Ideal Gas Law.
If you write a news blog for a living, there’s not much better than a discussion breaking out on it over a scientific calculation (if you want to fully understand why this is so refreshing to us, listen to yesterday’s This American Life).
That’s why we were delighted to receive reader Elizabeth Brown’s correction to the good professor’s correction on Saturday evening.
Your article “Xs, Os, and the Ideal Gas Law” needs at least one further refinement to understand the drop in the pressure in the footballs.
Atmospheric pressure isn’t constant, even at sea level. The 14.5 psi that the physics professor gave you is a rough approximation of what it is. To get a better approximation, you should use the actual atmospheric pressure, i.e., the barometric pressure. Most weather stations report barometric pressure in inches of mercury and so the weather service numbers would need to be converted into pascals.
The barometric pressure in Boston on Jan. 18, 2015 at 3:54 p.m. (about when the footballs would have been tested) was 29.9 “Hg (101252.762 pascals) and dropped to 29.69 “Hg (100541.622) and at the same time the outside temperature dropped from 50 F to 48 F. If the Patriots’ footballs were only inflated to 12.5 psi (as the news conference indicated), which is about 86184.466, then the starting pascal pressure for the footballs was 187437.228.
Furthermore, assume that the indoor temperature was 72 F (295.372 Kelvin) and the outdoor temperature was 48 F (282.039 Kelvin) by halftime. The pressure in the footballs would be 178976.36996 by halftime.
Then subtract out the atmospheric pressure, which was 29.69 “Hg (100541.622), which leaves 78434.74796 pascals in the footballs or 11.375 psi, which is about 2 psi (1.625 psi) less than the 13 psi that the NFL prefers the footballs to be at.
The only report that 11 of the 12 footballs were about 2 psi under comes from ESPN and has not been confirmed by anyone else. The 12th football also reported was less under inflated than the others but that can easily be accounted for if it started out at above 12.5 psi.
Anticipating what NewsCut’s physics-savvy readers might notice: It’s true, the Patriots don’t play in Boston, so I suggested researching the barometric pressure at the nearest airport to Gillette Stadium in Foxborough, Mass., which would probably be Norwood. There, Ms. Brown learned, the atmospheric pressure reported was the same as that reported in Boston.
Meanwhile, Patriots coach Bill Belichick called a news conference on Saturday, and didn’t use any of this information — this science, if you will — to explain what happened, preferring instead to insist that rubbing the footballs as part of the normal game preparation, combined with “atmospheric conditions”, raised the air pressure inside the ball as officials measured it.
Suffice it to say, the reporters covering the news conference didn’t have any greater knowledge of physics than Belichick does so there was no one to check his work.
Belichick invited the reporters to try there own experiment to confirm what he claimed is true. None did, but they didn’t have to.
The Ideal Gas Law’s role in the situation has already been confirmed by researchers at Carnegie Mellon and Head Start Labs, who recreated the conditions of last Sunday (see pdf).
“We took 12 brand new authentic NFL footballs and exposed them to the different elements they would have experienced throughout the game.” said Thomas Healy, founder of HeadSmart Labs. “Out of the twelve footballs we tested, we found that on average, footballs dropped 1.8 PSI when being exposed to dropping temperatures and wet conditions.”
During testing, twelve brand new footballs were inflated to 12.5 PSI in a 75 degree Fahrenheit room.This was to imitate the indoor conditions where the referees would have tested the footballs 2 hours and 15 minutes before kickoff. The footballs were then moved to a 50 degree Fahrenheit environment to simulate the temperatures that were experienced throughout the game. In addition, the footballs
were dampened to replicate the rainy conditions.HeadSmart Labs found that on average the footballs dropped 1.1 PSI from the 25 degree temperature change alone. The Lab also found that when the leather was wet, the ball dropped an additional 0.7 PSI. In combination, it was found that on average the footballs lost 1.8 PSI with a max of 1.95 PSI from exposure to game day elements.
Meanwhile, Bill Nye the Science Guy, who’s a mechanical engineer and media darling, insists there’s only one way to drop pressure by 2 psi — with an air valve.
He’s wrong and the calculations above prove it. It’s also worth noting he’s a Seattle Seahawks fan, whom the Patriots will play next week in the Super Bowl.
You can’t fake your way through physics.
Update 1/26 9:36 a.m. – Scientists agree that a football will lose air pressure when moved to a cooler place (The Boston Globe).
