Pressure Testing a Football to NFL Standards

Testing a football for pressure loss between inside , and outside in winter. NFL Rule 2, section 1 states that the a legal football must be between 12.5 and 13.5psi
static.nfl.com/...
Given the controversy about the AFC Champion Patriots using deflated balls to advance to the Super Bowl, here is a test and scientific analysis of the results.

[@CLTaggart]

Even my 5 year old daughter knows that moving something with warm air into cold air will lose pressure. However, with all the speculation, my daughter and I took it to the next level by taking a NFL football, autographed by Don Shula (seemed fitting), inflated it to 12.5 psi at 72 degrees. We then put it in our refrigerator at 44 degrees for 80 minutes. The pressure dropped to 10.5 psi. Here is our KZbin video: kzbin.info/www/bejne/a2PXpqyQadeZaM0

[@jungchoigt]

Great demonstration. Well done. Your calculations at the end neglected the ambient air pressure. The pressure gauge is measuring the difference between one atmosphere and the pressure inside the ball. One atmosphere is about 14.7 psi = 100,000 Pascals. So your P1 = 14.7 + 13 = 27.7, and P2 = 14.7 + 9 = 23.7. In your equation, then, 189,630 Pa/294K = Pout/280K = 180,600 Pa = 26.2 psi absolute = 11.5 psi relative. So your ball should have measured 11.5 psi outdoors. I was surprised that you had only 9 psi - must have lost some air in the measuring process. Similarly, solving for the outdoor temperature at 9 psi relative, we get 256.6 deg K, or about 2 deg F.

[@jumbi555]

Yes. I thought the same. Which means that the drop in temp alone would account for the difference. Why doesn't the nfl use a better method of standardizing their fotball psi's.

[@silvermediastudio]

Jung Choi This is the result of public education. People think they know what they are doing, and apply pseudo-scientific methods, but miss so much. As you say, he is using gauge pressure not absolute pressure. Changes the result from a 15% delta to a 7% delta.

[@angelagibson9874]

Thank you

[@henrywasserman]

One piece of information you left out. You should have tried the same football, left it inside for the same amount of time and see what happened. A seven year old football might not be capable of holding 13 psi regardless of the temperature.

[@Kensingtonlane]

Also your pressure gauge is only in .5 lb increments.

[@OnTheWorkbench]

That is fair, if I had a gauge that was accurate to a small amount, I would have used it, but I do not. This is just to show that weather may have had something to do with it all.

[@dontishler3000]

Since the NFL has now said that the balls were changed at the end of the half, and the pressure didn't change at the end of the game, could you do the test again showing those parameters. I assume, if the temp was constant, the pressure wouldn't change if they were refilled in the outside temps. Also, the effect of the rain on the balls would also decrease the pressure too I assume.

[@OnTheWorkbench]

If the balls were pressurized outside (or in similar temperatures) there any deflation due to thermo contraction could be ruled out by basic chemistry.

[@searcherT]

a few things I never heard from the NFL or the Patriots is that : What temperature did you inflate the balls originally? The balls when tested what were the conditions and how long were they subject to that condition.? What are the measurements of a football at the (used room temp) and by that I mean the inner volume at temp of football when inflated as opposed to game play temperature. FYI I do not know the exact measurements of a football but the indefinite integral of a football f(x) 2-1/2*(x-2)^2--------- f'(x) -1/6+(x-6)*x^2 May be some one can take it a little further since I have no relationship with the Patriots.

[@greenworm9116]

there you have it. Case closed.

[@billair5642]

The ball was 7 or 8 years old.

[@Kensingtonlane]

Either your hands are really big or that ball is too small and round.

[@fmaguire]

Interesting, thanks. Did you bring the ball back in to see if the psi rose back up?

[@OnTheWorkbench]

I should have, but did not do one on camera or measured with any tool; I think there was a loss of air (presumably out of the valve). After sitting in my kitchen for about a day, by feel it is under pressure. I think the next logical test would be to test a statistically significant number of footballs, and to investigate the valve stem specifically to check for air leaks due to expansion/contraction under changing temperatures.

[@richardstreetman998]

As pointed out earlier, your math is wrong; the pressure readings must be absolute atmospheric pressure so you must add 101,353 pascals to the initial pressure and subtract it from the end result. That would give you a theoretical pressure of 11.666 which is close to the 11.3 reading taken when the ball was intercepted. Your test was bad because you used inappropriate equipment and test ball. You should remove this video or post an apology.

[@truepatriot6388]

Check out DeflateGate Football Science Explained at: kzbin.info/www/bejne/npeboIRqp82FY6M It examines Belichick's claims and gives important clues for solving the mystery of the football pressure drop...