Deflate Gate
Deflate Gate Examined
By: Steve Driscoll
Purdue University, Columbus Campus
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Deflate Gate
Abstract
Several students along with staff members of the Mechanical Engineering Technology program
at Purdue’s College of Technology, Columbus campus completed multiple tests to investigate
the measureable performance characteristics in relation to different inflation pressures of a
National Football League regulation football made by Wilson Sporting Goods.
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Deflate Gate Examined
Introduction
On Sunday January 18, 2015 the New England Patriots defeated the Indianapolis Colts in
the American Football Conference (AFC) Championship game by a score of 45-7. The game was
played on a cool and rainy evening in Foxborough, Massachusetts. Hours after the game a tweet
flooded the sports world; (Kravitz) “Breaking: A league source tells me the NFL is investigating
the possibility the Patriots deflated footballs Sunday Night. More to Come.” At 9:55pm EST the
latest NFL controversy was born, and quickly referred to as ‘Defalte-Gate.’ Over the course of a
few short hours Deflate-date exploded as major media outlets reported on leaked information
from the NFL.
ESPN was the first to report (Mortensen) “the NFL’s initial investigation found 11 of 12
footballs used by the New England Patriot offense were inflated 2 psi below what’s required by
the NFL regulations” during the Patriots victory over the Colts. According to the NFL Rule Book
(ref-ump) “each team must deliver 12 footballs to the Referee 2 hours and 15 minutes prior to the
starting time of the game.” The Referee is the sole judge as to whether the footballs delivered by
the respective teams comply with these specifications. The football is under the supervision of
the Referee until they are delivered to the ball attendant just prior to the beginning of the contest.
(Mortensen) “ESPN Sports Radio 810 in Kansas City reported that the Patriots’ footballs were
tested at halftime, and were discovered to be low in air pressure and were inflated to proper
specifications.”
Many people wondered what advantage would there be to playing with an underinflated
football, at the reported 10.5 psi mark? Luckily, at the Purdue College of Technology campus in
Columbus we have equipment that can determine what advantages can be gained from playing
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with a 10.5 psi football versus one at 12.5 psi. The students involved wondered why rely on the
varying “experts” on television and discover the plausibility using math, technology, and
science!
Materials/Team Overview
Beginning on January 27, 2015 a team led by Professor Dr. Joseph Fuehne and his
students; Steve Driscoll, Jordan Ezell, Caleb Faulkner, Kevin Raisor, and Jesse Ritchie, with
guidance from Metrology Lab manager Matthew Ferrell commenced the process to develop a
test plan. The test plan was used to create a structured program for recording measurements to
determine the measureable differences between footballs at varying pressures. The footballs used
are the exact same footballs that would be used in gameplay. They are marketed by Wilson
Sporting Goods as “The Duke”. According to the Wilson website it is the official game ball.
Each football was purchased at local sporting goods stores in the greater Indianapolis region at a
cost of $100 each. “The Duke” is not the average ball used at barbeques and tailgating parties. A
total of three footballs were used. The same pressure gauge and Nike football pump was used for
the entire experiment and the accuracy of the gauge was verified by internal processes. Two tests
would be performed; a compression test and an environmental exposure test.
Compression Test (Load v Pressure)
The compression test would determine the possible benefit of a team playing with a
football at a lower air pressure than what is allowable. An automated compression testing system
manufactured by Instron was chosen to conduct the compression test. The Instron software
allowed our team to measure the force required by the hydraulic arm of the machine to compress
the ball one quarter of one inch. The 0.25” was used to develop enough data to make a best curve
data plot. The data in figure one shows the results of the load required to reach 0.25” and the
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inflation pressure of the ball before and after the conclusion of the compression test. Included in
figure one is the percentage difference in load required to compress the ball 0.25” in relation to
the minimum specification from the NFL. The data below is compiled from an average of the 3
samples run through the same pressure range. The test began with the first ball at 8.5 psig and at
the completion of each run the same ball was then inflated to the next pressure. At the
completion of the 14.5 psig point, the next test sample was used until all samples were
exhausted. The pressure of the ball was checked pre-test and post-test to ensure the football
pressure remained constant to observe any recordable changes.
The results from the compression test revealed some intriguing findings. The change in
load from varying pressures was not linear. However, taking the entire range into account there
was an average change in load of 6.7%. The change from 8.5 psig to 9.5 psig was greater than
the change from 12.5 psig to 13.5 psig. Several members of the testing team found to be
noticeable difference in feel of the ball when a large change in pressure took place. The results
also confirm with basic principles of a gas under pressure. At higher inflation pressures there will
be more energy required to compress the ball then a ball at lower inflation pressure. The
appendix has an additional graph with each individual run compiled showing the varying lines of
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data in relation to pressure. The next step was to determine if the weather could have played a
role in lowering the pressure of the ball.
Environmental Exposure Test
One theory that was introduced was if a game being played outdoors in January at Gillette
Stadium in Foxborough, MA played a role in the inflation pressure dropping below the legal
limit. The footballs are given to the Referee who is located in a conditioned air environment, and
then the footballs are played in the elements. The game time temperature in neighboring
Norwood, Massachusetts was 52.0° and with a steady rain (Weather). According to the Ideal Gas
Law if the temperature of a container is increased, the pressure increases; furthermore if the
temperature of a container decreases the pressure decreases. We used this law as our previous
measurements indicated there was a minimal change in the footballs dimensions as the diameter
of the ball only changed a max of 0.002”. Thus we felt the Ideal Gas Law was the most relevant
to our study. The equation for the Ideal Gas Law is simply the initial absolute pressure (P1)
divided by initial temperature in Kelvin (T1) equals final absolute pressure (P2) divided by final
temperature in Kelvin (T2), or graphically demonstrated in figure 2.
In our initial experiment we used 2 footballs, one at 13.5 psi and the second at 12.5 psi and
allowed them to reach equillibrium in the temperature controlled environment in the lab. The lab
environment is a stable 68°F. The footballs were placed inside of a refridgerator that had a
measured temperature of 33.8°F for 60 minutes. At the conclusion of the time the pressure of the
footballs were measured again. We did not believe 60 minutes was enough time to reach
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equillibrium however we wanted to see if there was a correleation between the equation above
and what actual results showed.
The data compiled showed the measured end pressure and the calculated pressure derived
from the Ideal Gas Law was a good estimation of the change. There was a difference of 4.06%
on average from the calculated to measured values. The environmental exposure test will
continue as there is a need for multiple repeats to ensure thorough data quality. However, with
this initial data we can calculate the expected result of this test if we use a 13.5 psi and 12.5 psi
sample and place them into a chiller at 52°F to represent the same conditions on game day.
According the Gay Lussac Law and using an error of 4.06% the results are expected to be in the
range shown in figure 4.
Further testing is needed to explore the football’s behavior when lowering the temperature
a smaller amount as best to simulate the conditions at gametime.
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Test Observations
There are a few noteable observations during the test that should be noted for further
discussion or testing. The football pump needle made a very poor seal when inflating the
football. A noticeable amount of air was felt coming around the side of the needle when inflating
the football. The amount of air leaving the football when removing the pump needle from the
ball also released a small amount of air each time. The team estimated that with each removal of
the valve 0.1 psi was released as we closely observed the behavior of the interaction between the
needle and the football. Thus, it could be plausible that if a ball is inspected several times in
succession without being inflated could be subjected to a significant loss in pressure and should
be noted for further testing.
Review
Is it possible the New England Patriots gained a performance advantage with a football that
was measured below minimum allowable air pressue? As our data shows there is a 10 % increase
in compressibility of a football at 10.5 psig in comparison to 12.5 psig., thus it is plausible the
Patriots gained a performance advantage from a ball control standpoint. Tom Brady would
therefore be able to throw one of his wicked hard fastballs a bit easier in the rainy conditions due
to the increased compressibility of the football.
Is it possible the weather had an effect on the pressure of the football and contributed to the
11 of 12 footballs measuring below allowable specification? The data collected along with the
calculations derived from the Ideal Gas Law in addition to the error we measured in relation to
our test it appears the weather could account for as much as 64% of the total pressure loss. In
addition to the environmental loss, if a football is checked using similar equipment as what we
have, which was standard issue there would need to be a very quick measurement as pressure is
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lost the entire time the needle is pressed through the air bladder valve. If the balls that were
inspected were not allowed to reach equillibrium in the air conditioned space then a loss of 64%
would be instrumental.
Conclusion
The testing team was able to prove that there is measureable difference between force and
its relationship to inflation pressure of an NFL football. The team was also able to prove using
calculations and measureable data points to determine the weather would contribute to a
significant loss of inflation pressure of an NFL football using the current process being used by
the league.
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References
1. Kravitz, B. (2015, January 19). Breaking: A league source tells me the NFL is
investigating the possibility the Patriots deflated footballs Sunday night. More to come.
Retrieved January 30, 2015, from
https://twitter.com/bkravitz/status/557053826415755265
2. Mortensen, C. (2015, January 21). 11 of 12 Pats footballs underinflated. Retrieved
January 30, 2015, from http://espn.go.com/boston/nfl/story/_/id/12202450/nfl-saysnew-england-patriots-had-inflated-footballs-afc-championship-game
3. www.ref-ump.com . (2014, January 1). Retrieved January 30, 2015, from http://refump.com/services__rule_books/national_football_league
4. Weather History for Norwood, MA. (n.d.). Retrieved January 30, 2015, from
http://www.wunderground.com/history/airport/KOWD/2015/1/18/DailyHistory.html?M
R=1
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Appendix
NFL Rule 2: The Ball
(NFL.com)
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Appendix
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Appendix
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Appendix
Ball 1 Compression Data
Appendix
Ball 2 Compression Data
Appendix
Ball 3 Compression Data