Deflated Balls and a Little Fun
January 25, 2015
I don’t know if you have been paying any attention to the Super Bowl but there is a big controversy over did the Patriots play with under inflated balls in the Colts game. I thought I would weigh in.
I see where Belichick finally filled a football with air inside the stadium office to 12.5 PSI, the minimum allowed, and then took the ball outside where air was colder. They waited a while and then checked the PSI of the football. It had dropped 1.5 PSI or to 11 PSI, to put it simply, it had deflated. That is the law of physics at work. The pressure in the football will decline in direct proportion to the decline in temperature.
Pump up a football to 12.5 PSI at 72 degrees inside the stadium and then cool the ball to 47 degrees on the field and the PSI will drop to 8.2 PSI. (P1/T1=P2/T2) The question should be, why did the Colt’s balls not deflate, not why did the Patriots play with under inflated balls because balls that do not deflate in cold weather are the ones that are defying the law of physics.
What is interesting is footballs have been inflating in hot weather and deflating in cold weather since the game was invented.
If a ball is filled to the minimum 12.5 PSI allowed, then temperature on the field must be equal to or warmer than the fill up temperature for the ball’s PSI to be legal, but the field temperature cannot be more than 8% warmer than the fill up temperature or the ball will become over inflated and not be legal.
If the ball is filled to the maximum 13.5 PSI allowed, then the temperature on the field must be equal to or cooler than the fill up temperature for the ball’s PSI to be legal, but the field temperature cannot be less than 7.4% cooler or the ball will become under inflated and not be legal.
Think about how many games are played where the temperature inside the stadium office and on the field is different by more than 7 or 8% . My guess is that most games have been played with illegal balls, either over inflated or under inflated, due to the temperature on the field being different from the temperature when pumped up.
Prediction: NFL will install temperature control boxes on the sidelines that will maintain the ball at 72 degrees. Oops, atmospheric pressure also affects the pressure of the ball. Oh well, you can’t control everything.
If you want to change the pressure in the football for the game you don’t have to do anything to the ball, all you have to do is change the temperature of the room where it is filled.
Question: Did you do anything to the ball?
Answer: Absolutely not!
Remark: I was cold, so I turned up the thermostat; I mean it was 47 degrees outside.
You can get extra points if you can tell me what the ball PSI would be on the playing field if the room temperature was raised from 72 to 76 assuming the fill pressure was set to the minimum of 12.5 PSI. Remember, the field temperature was 47 degrees.
Life is so much fun to observe. I laugh a lot.
Owl update: No Owls, but a pair of kestrels showed up yesterday. Also, Roark the red-shoulder hawk, has been seen eating grubs in the backyard when it rains.
All the best,
Carlos and Donna Royal