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Belichick's 'DeflateGate' Explanation Falls Flat on Technical Details

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danwelsh in SD
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Iron
Charles, Boyle, and Belichick
danwelsh in SD   1/29/2015 8:55:02 AM
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One should alwasy check the worst case scenario to decide if something is plausible.  If we assume the valves of the gamesballs actually work (so no air molecules exscaped the ball) and that the leather didn't stretch over one football game of use (so that the volume of the ball is constant), then the ideal gas laws tell us the following:

Pressure at start/Pressure at the end= temperature at the start/temperature at the end.

We assume the balls were inflated to the minimum possible pressure of 12.5PSI because every quarterback wants them as soft as possible, and we assume they were inflated at an ambient temperature of 30C (86F) because Belichick's office is full of hot air. We know the final pressure was 11.0PSI, so we calculate that the temperture of the balls was -6C (20F) at the end of the game.  So this is just at the limits of being plausible.

My questions of this process are simple; how did one ball not lose any pressure when the simplest version says it should have lost 1PSI? and how did they ever play a game in Green Bay that very day without having "deflategate two"?

 

 

jhankwitz
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Platinum
Re: Charles, Boyle, and Belichick
jhankwitz   1/29/2015 9:17:38 AM
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You're assumptions are right, but having a minimum 12.5PSI requirement does not mean that they met that standard.  I don't think there is a documented and verified record of all ball pressures before every game.  Also, this deflation likely occurs during every game played in cold weather.  Difference here is that someone brought it to the attention of officials for the first time, and the media has, as usual, jumped in on the opportunity to once again create a big story about something insignificant.  I have yet to see documented records of all ball pressures taken during the last half of games played in freezing weather.  This may be the first time anyone has bothered to check.  This appears to me to be just another media hype, like the impending destruction of New York this past week.  --John

tluxon
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Gold
Re: Charles, Boyle, and Belichick
tluxon   1/29/2015 2:04:14 PM
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Of COURSE it's all media hype - just one more distraction from the great transformation that's taking shape all across the globe right now.  Ball pressures have never been monitored all that closely and NFL quarterbacks have always taken it upon themselves to adjust the pressure to something that feels right in their hand.  That is, unless a coach overrides the QB and insists on a lower pressure to make sure the other ball carriers will have better ball security.

The reason teams have always used a ball that's inflated more than the others as a "kicking" ball is so that it will rebound better off the foot and be more prone to being fumbled by a receiving team.

Critic
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Platinum
Football Inflation
Critic   1/29/2015 9:51:00 AM
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One would think that even if the football is a little deflated, it wouldn't give one team a competitive advantage over the other team because both teams handle the same ball (unless a properly inflated ball is substituted during the game).

To keep keep balls within the regulation 1 PSI (12.5 - 13.5 PSI) pressure range, temperature must be considered if it is expected to change during the game, or if the ball is inflated indoors and then brought outdoors where the temperature is different.  A 20 °F temperature difference changes the inflation pressure by about 1 PSI (no, not 2 PSI).

Technology could help with ball inflation.  Footballs could be fitted with built-in, lightweight, low-profile pressure monitors.  These could have visible digital displays, or the pressure could be remotely monitored like automotive tire pressure sensors.

Alternatively, groups of  balls could be inflated for different ranges of target temperatures.  Then, balls appropriate for the present temperature would be used for the game.  This could require a lot more footballs, though, if the temperature is expected to vary widely during the game (or between the time the balls are inflated and the end of the game, which could easily be 4 - 5 hours).

As a benchmark, typical automotive tires lose roughly (depending on the inflation pressure for the particular tire) 1 PSI for each 10 °F drop in temperature.  Keep in mind that tire pressure is generally higher than football pressure, so the pressure change is larger. 

ttemple
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Platinum
Re: Football Inflation
ttemple   1/29/2015 11:21:28 AM
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Critic,

I don't think that both teams use the same balls.  Not sure though.

SKROGGER
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Iron
Re: Football Inflation
SKROGGER   1/29/2015 11:34:25 AM
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Ummm, wasn't the score 45-7 ?

tluxon
User Rank
Gold
Re: Football Inflation
tluxon   1/29/2015 1:00:23 PM
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The final score is rarely a good indicator of what separates two teams.  If the deflated balls prevented one or two early game fumbles that may have become turnovers, the momentum of the game could've swung the pendulum in a completely different direction.  In the pro-am racquetball tournaments I used to play many times a year, it was not that uncommon for a player to win one game 15-0 and lose the next 0-15.  Momentum and focus can and often do take wild swings and can make one side of a scoreboard seem stuck while the other spins up quickly.  The Patriots are clearly the better team, but victories that look big on the scoreboard are not always indicative of what little differences would've made for a much more competitive game.

Nonetheless, if it was my league, I would let the teams play with whatever balls they both agreed to, and permit any innovations that come out of it to be rewarded.

ChuckMahoney
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Gold
Re: Football Inflation
ChuckMahoney   1/29/2015 2:48:49 PM
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My understanding is that each team plays with it's own balls. Sorry, I just had to.

78RPM
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Platinum
Re: Football Inflation
78RPM   1/29/2015 1:52:19 PM
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It is my understanding that the offensive team selects its balls. The soft ball was detected by a defensive player during a reversal.

Charles' Law tells us that if the volume of a confined gas is constant, the pressure is directly proportional to the absolute temperature.  So if the temperature changes from 55ºF to 35ºF, this is a difference of 11º Kelvin.  Thus, the pressure would change by 11/274 or 4 percent.  4 percent of 13.1 lb. is .53 psi difference.

Critic
User Rank
Platinum
Re: Football Inflation
Critic   1/29/2015 3:45:21 PM
@78RPM:

I am not a football expert, but I do know a little about the Ideal Gas Law.  Charles' Law relates temperature and volume, not pressure.  This might seem trivial now that we know more about how gases behave, but way back when, the Ideal Gas Law was an extension of Charles' Law, effectively making it obsolete for applications like this one (how old are you, anyway?).

I am sorry to say that your calculations are also incorrect.  You have to use absolute pressure, not gauge pressure (relative to atmosphereic pressure).  So, take 4% of about 27.7 PSI and you will arrive at a more accurate figure.

In a football game, the players do not always have the option of selecting a ball.  Sometimes they are forced to play with the ball that is in play!

78RPM
User Rank
Platinum
Re: Football Inflation
78RPM   1/29/2015 8:23:20 PM
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@Critic,

Ah, darn.  I forgot to use absolute pressure instead of gauge pressure. Right you are!

I attempted to do an approximation.

Thanks for insulting my age. In a position of power, I will remember to do the same to people of your presumed age. Don't look down your nose at me because of age. Were you drunk when you wrote that?? Pretty harsh in your rebuttal and not very civil.

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