Ideal Gas Law and the NFL

We have reports that 11 of 12 balls checked after the AFC Championship game were underinflated.  We have a statement that [one, some, all] was/were 2 psi below acceptable pressure.  Using PV=nRT, with absolute pressure (ball pressure +atmospheric pressure) and game time temperature we can calculate what the change in temperature would do to the ball.

If we assume:

  • volume, number of atoms, and R (gas constant) all remain unchanged
  • the balls were pumped to 12.5 psi at some initial unknown temperature
  • the air temperature within the ball was the same as the outdoor temperature at the time the game ended (46F)
  • the gauge pressure of the ball was 10.5 psi immediately after the game ended

We calculate an initial gas temperature of 88.2 F.

Basically a drop of 1 psi for every 20 F change.  The Chart below is set using the ending pressure (10.5 psi) at the ending temperature (46F).

PT

Questions that remain:

  • What was the temperature of the air in the ball when the initial reading was taken by the officiating crew?
    • We may never know this, but testing the pump used can help get a handle on what the temperature could have been
  • What was the type of pump used to inflate the balls?
    • I have used air compressors that significantly heated the compressed air. The cheap compressor that filled my air mattress was quick, but I was not happy when I woke up in the morning with a less than full mattress under me.
  • What was the type of gauge used to measure the pressure (psi) of the balls? What was the accuracy of the gauge (+/- 0.25 psi, +/- 0.5 psi, etc.).
  • What was the loss in pressure every time a gauge was used?
    • When a needle is inserted in the bladder, a small amount of air is released. Providing an estimate for potential losses would be beneficial in understanding if there was other influences that cannot be accounted for.

The responsibility lies with the officials to assure that the balls provided are suitable for game use.  If there are questions, or concerns get them fixed.  If it’s pop warner or high school or NFL, take control and make sure you have a ball that is suitable.

If you’re the opposing team and you have a concern: don’t keep it to yourself and wait until after the game – alert the officials to the concern and get on with the game.

Update 2

Update 3

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3 Responses to “Ideal Gas Law and the NFL”


  1. 1 Bradly December 23, 2016 at 2:36 pm

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  1. 1 The NFL and the Ideal Gas Law – Part 2 | ChaSch Trackback on May 13, 2015 at 10:25 pm
  2. 2 Part 3 – The Ideal Gas Law and the NFL | ChaSch Trackback on May 14, 2015 at 5:08 pm

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