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Monday, July 23, 2018

Unlocking the deflation puzzle

‘Gas physics’ might explain the low pressure found in some balls used for the AFC championship game.

By: New York Times | Published: February 8, 2015 12:25:56 am

Yep, it’s for real. The law firm representing the NFL (Paul, Weiss, Rifkind, Wharton & Garrison) has reached out to Columbia University’s department of physics to recruit an expert on “gas physics” to help determine, as has been reported, the “environmental impacts on inflated footballs”.

This is one of those rare times when the jocks turn to the nerds, so fellow fans of molecules and momentum —  climb out of that gym locker you were stuffed into —  this is our moment. Stand tall. And do the wave.

OK. Onward to the exciting world of gas physics. (Note to self: Save all gas physics jokes for when kids get home from school.) Here’s what you need to know:

The pressure in a football filled with air comes from molecules of the air slamming into the inner walls of the football, pushing the ball’s skin outward. It’s kind of like a bunch of wild kids running around in a room —  as they slam into the walls, they too push outward.

Now, just as more kids, crammed into a smaller room, running ever faster will result in a greater outward push —  a greater pressure —  so too will more air molecules crammed into a smaller volume, rushing around faster, yield a greater pressure.

Physicists make this precise with a formula from the 1800s: PV = nRT. P stands for pressure; V for volume; n comes from the number of gas molecules; R is, well, trust me, you don’t have to worry about it; but T, the last symbol, is key: It stands for temperature.

How did temperature get in on all this? Well, temperature is nothing but the average speed of the air molecules. So, the hotter the air, the faster the molecules and the more pressure they collectively exert as they careen into the inside of the football’s skin. That’s the role of the “T” in the formula.

And that’s where the lawyers come in. They want to talk to a physicist, I presume, to help determine if a drop in temperature —  a slowing of the air molecules inside the football —  can explain the low pressure that was found in some of the balls used in the AFC championship game two weeks ago between the New England Patriots and the Indianapolis Colts. Or maybe they just want to increase their billable hours.

So, could a drop in temperature do the dirty deed? The bottom line is that the little formula can explain a drop in pressure to nearly 11 pounds per square inch.

I’ve heard various numbers tossed around for the pressures of the offending footballs, some in this range, others a touch lower. More exact analyses  will require the nitty-gritty details: What was the temperature when the footballs were inflated? What pressure were they initially inflated to? How accurate are the pressure gauges that were used?

Without this information, all we can do is estimate the pressure drop. But a word to the wise. All current and would-be ball deflators: You may want to brush up on Physics 1.

Now, I’m waiting for the day that the NFL needs some string theory calculations.

P.S. Here’s your prize for getting this far. The next time you hear Alex Trebek say, “This letter is known as the ‘ideal’ or ‘universal’ gas constant,” your response is, “What is R?”)

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