Deflate-gate: Mechanical Engineering Weighs-In

Everyone is talking about what is being called ‘deflate-gate’ and no matter where you stand on the subject there is a technical side to this story.┬á New England Tech’s Mechanical Engineering┬ Department Chair,┬áDean Plowman talked to RJ Heim of WJAR yesterday.

From WJAR news report:

With ESPN reporting that 11 of the 12 Patriots’ game footballs were 2 pounds per square inch below the regulation minimum of 12.5 pounds, it’s important to note that different air temperatures make a difference on the pressure.

“The temperature is always going to be a variable, just like (with) your car tires. The car tires are always changing their pressure based on (air) temperature,” Dean Plowman of the New England Institute of Technology said.

The gas going in the football, presuming it is air, is mostly nitrogen at 78 percent and oxygen at 21 percent. But with higher humidity — it was raining at the Sunday night game — water content can be as high as 6 percent, displacing the previous gasses.

“So, if I fill a football at 71 degrees to 12.5 psi (pounds per square inch) and I take that ball outside to 51 degrees, the pressure inside that ball is going to drop proportionally relative to that temperature drop,” Plowman said.

So, with a 20-degree temperature drop, that would mean at most a half pound of pressure difference inside the ball.

Even accounting for the temperature difference and its effect on the pressure in the football, it would still leave the balls in question with reportedly a pound-and-a-half of pressure below the regulation limit. How that happened is the question.

“To do something like that is a lot of work. So, why would you even risk, you know, doing that?” Plowman said.