The NFL and the Ideal Gas Law – Part 2

CaptureI posted a while back about this topic.  But the official report came out last week and punishment followed shortly after, so I thought I would add some more of my thoughts.

There were two things I found interesting from the Well’s Report recently released.  In the report there is the evaluation performed by Exponent.  Where they were tasked with evaluating the scientific principles at play that may have accounted for the pressure drops observed on January 18, 2015. I have concerns that deal with the initial conditions of the footballs – What was the actual initial pressure?  and What was the temperature of the gas at the time of the initial measurement?

  • Two gauges were used on game day (logo & non-logo) to read pressures.  The gauges had readings that differed between 0.35 psi and 0.75 psi.
    • I would have tried to reconcile the instruments to some standard (i.e. to adjust the measured readings to a reference), and tried to ascertain which gauge was used and when during the day in question, January 18, 2015.
      • For example, the logo (higher reading) gauge could have been used pre-game to give a measurement that could differ up to 0.75 psi, meaning the gauge could read 12.5 psi, while the non-logo gauge would read it as 11.75 psi. Now if the non-logo gauge would have been used at half-time, then the pressure drop due to temperature along with the initial discrepancy would need a drop to the 10.5 psi measured (0.75 psi from device difference and 1.25 psi from temperature change).  Meaning the initial temperature of the gas in the ball would only need to be 73.1 degrees Fahrenheit.

(The Wells report (Exponent analysis) attempts to reconcile the ‘what ifs’, but from a quick reading the permutations provided seem to muddy the water more than clear the issues.)

  • The starting temperature used in their calculations was the temperature in the room where the balls were measured
    • Questions
      • Were the balls already inflated before arrival at the stadium? And if so, how would you measure the temperature of the gas at the time of the initial pressure readings? Or would the assumption that the temperature of gas in the ball was equilibrated to the ambient temperature of the room be adequate?
      • Were the balls completely flat (free of gas) and then inflated at the facility with the home team provided pump?
        • What was the temperature of the gas as it left the pump?
        • What was the time between inflation and the check by the referees? What was the temperature of the gas at that time as the air cooled to the ambient room temperature?

(The Wells report does not clearly define the timeline; it does say that Game balls are selected by Tom Brady 3 to 4 hours before game time.  Assuming these are already inflated and need a final adjustment to the reported 12.5 psi preference prior to delivery to referees.  The temperature of the gas in the balls may very well be near ambient temperature, unless they are stored near a heat source in the building.  The issue is not discussed, just an assumption that ambient room temperature is the starting temperature.)

The Exponent analysis does admit that specific scenarios could account for a pressure reading difference of 2 psi as reported on game day.  However, the more indicative statistic would be the pressure drops recorded between the Patriots’ and Colts’ game footballs, where the Colts’ footballs lost an average 0.45 psi from the initial pressure readings and the Patriots’ footballs lost an average 1.02 psi.  Although this may be skewed by the fact that only 4 footballs from the Colts were gauged, while 11 Patriot footballs were measured.  This evidence supports the report’s conclusion that manipulation took place, with the assumption that the Colts’ and Patriots’ footballs were exposed to the same temperatures and environmental conditions.

The main report has the “Deflator” character and his Patriot cohort, with communications between the two discussing manipulating game balls and implicating Tom Brady’s involvement.  McNally and Jastremski had communications May 9, 2014 using the term “Deflator” for McNally (Bird). Another series of communications on October 17, 2014 brings Brady into the communications.  It appears that this may have been going on for home games the entire season or longer (McNally has only worked home games for the past 2 seasons).  The Colts said they were suspicious of ball tampering after a Week 11 Colts vs. Patriots game in Indianapolis where two intercepted balls were described as spongy or soft when squeezed.  McNally was not the “deflator” in that instance (no mention of him participating as a locker room attendant for away games), so maybe Jastremski has another patsy or is doing the tampering himself.

Overall enough information is provided to warrant the 4-game suspension of Brady.  The science is a little shaky but enough numbers are thrown in to discourage the general public from further examination.

Update 3


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