Guest post by Alec Rawls
Just fill the ball with warm humid indoor air, then when it temperature-equalizes with the 25°F cooler outdoor air on your AFC Championship playing field some of the water vapor in the ball will condense into water, leaving less air in the ball, solving the great mystery: how did the footballs used by the Championship winning New England Patriots show 12.5 psi of inflation pressure in the official pre-game check but only 10.5 psi when checked at halftime?
There is also a decrease in pressure due to the cooling of the molecules that remain gaseous. Those air molecules are not zipping around as fast as they were so they exert less outward pressure on the ball. But according to the ideal gas law, if there were no reduction in the number of gas molecules in the balls it would have taken a large drop in temperature, about 40°F, to cause the observed drop in air pressure. So says Boston College professor Martin Schmaltz:
In order for a ball to register a 10.5 PSI in a 50 degree environment [the temperature on the field at halftime] but register a 12.5 PSI in the testing environment, the ball would have to have been inflated, stored, and/or tested in a 91 degree environment.
I verify Schmaltz’s calculations at the end of this post, and while I’m no expert in the field, I get the same answer he does.
It wouldn’t be hard to deliver balls to the pre-game pressure check with 91° air inside. Just inflate them in a 100° sauna shortly before testing, but the Patriots are adamant that they do not know why the air pressure in their balls was low at halftime and if they had inflated their game balls in a sauna they would certainly know it.
The Carnegie Mellon experiment
An experiment performed by a team at Carnegie Mellon provides empirical support for the Patriots’ claim to have done nothing unusual. The Carnegie experimentalists inflated a batch of footballs to 12.5 psi at a room temperature of 75°F, then let the balls equalize to a new ambient temperature of 50°F, resulting in an average pressure drop of 1.8 psi. (They also wet the leather balls to simulate the rainy conditions of the game, surmising that this might allow stretching that would reduce air pressure in the ball, but this seems likely to be a minor factor.) The Carnegie experiment is video-documented here:
So how to account for the difference between the Carnegie findings and the ideal gas law, which predicts that a much larger decrease in temperature would be needed to create the observed pressure drop? Barring experimental error, it seems that the difference would have to be explained by condensation. Gas was removed from the ball, not via an inflation needle but by conversion to liquid water. What do our blog-reading experts say? Is this the likely explanation?
The Carnegie group was not monitoring humidity (at least in the short video above), but if this is the explanation for their greater-than-ideal pressure drop then it could easily have happened to the Patriots the same way without anyone intentionally manipulating the inflation temperature or humidity. Still…
It must be common knowledge around the league that indoor inflation yields a softer game ball
The fact that the Colts’ balls did not show a similar pressure drop suggests that teams do know how to make these manipulations. Just as Patriots’ quarterback Tom Brady prefers to throw a less inflated ball, other quarterbacks
are known to prefer harder footballs.
If Colts quarterback Andrew Luck prefers a harder ball then all the Colts had to do is fill their balls pre-game with cool outdoor air. Ambient outdoor temperatures actually rose from pre-game to halftime so the temperature effect would have made their balls firmer. Also, moisture beyond what the cooler air could hold would never have made its way into the ball in the first place so wouldn’t there be any pressure-reducing condensation inside the ball either.
Players and equipment managers would surely have noticed over the decades how the conditions in which balls are inflated to regulation pressures affect ball firmness on the field. The basics are hard to miss. In cold conditions, inflate outdoors to get a firm ball, indoors to get a softer ball.
The existing pressure-test regimen, intentionally or not, leaves this room for teams to manipulate ball pressure to suit their preferences. The rule just says that air cannot be put into or removed from the ball after the pre-game pressure check. It does not regulate the conditions in which the balls are inflated going into the pre-game pressure check.
“Belichick rules”
If Coach Belichick had exploited this loophole to the max by inflating balls in the sauna then there would be a legitimate question whether this rule-bending constitutes cheating and there is plenty of history, both recent and ancient, to indicate that Belichick is eager to wring every advantage out of a loophole that he can. Where others may see exploiting loopholes as cheating, Belichick sees it as part of the game.
By the time he is done the NFL rule-book will contain at least a few “Belichick rules,” closing the loopholes he has so nicely pointed out, most recently by confusing the Baltimore Ravens about which Patriots players were eligible to receive passes. “It’s not something that anybody has ever done before,” complained Ravens coach John Harbaugh, “I’m sure the league is going to look at it and make some adjustments.”
Belichicks’ reward (besides a trip to the AFC Championship): he is now tied with Tom Landry for the most post-season coaching wins in league history, to which I say GO PATRIOTS! (That’s what you call “full disclosure.”)
But the full explanation in the present case seems to be that the Patriots filled their game balls with indoor air. If that is manipulation at all it must be utterly commonplace and well within the rules.
The biggest loser: Bill Nye, the phony-science guy
While real scientists keep acknowledging that the move from inside to outside can cause a substantial drop in football psi, Nye went on national television to proclaim that air must have been taken out of the balls with a needle. So that’s good anyway. Half the Northeast now knows that Bill Nye is an idiot.
Addendum: Gas law calculations
I was looking up how to calculate the expected pressure drop in a ball for a given temperature drop when I came across the claim from Boston College physicist Martin Schmaltz that, following the ideal gas law, temperature inside the balls would have had to be 91°F during the pre-game pressure check to account for the 2 psi drop in air pressure by halftime. In the exercise below I come up with a similar answer but I have no background in this stuff and am just following readily available information so don’t take my explication on authority (and please do note any inaccuracies in the comments).
When the number of gas molecules in a container is fixed (no gas escaping out through the bladder and no gas converting to liquid via condensation) then the ideal gas law simplifies to the general gas law, also called the combined gas law. Like the ideal law, the general law is said to be close to accurate so long as extreme pressures or temperatures are not involved. Mathematically, the general law just says that gas temperature, volume and pressure all vary in direct proportion to each other:
(P1V1)/T1 = (P2V2)/T2, where P1 is pressure at time 1, V1 is volume at time 1, and T1 is temperature at time 1.
In plain language, for the gas pressure in the Patriots’ footballs to drop by 7% the general gas law says that the temperature of the air in the balls must drop by 7% or the volume inside the ball must increase by 7% or there must be a combination of percentage changes in temperature and volume that add to 7.
The problem can be simplified further by assuming (as Professor Schmaltz does) that the volume of the space inside the football remains constant. (This won’t be fully accurate. When pressure in a ball drops the volume inside the ball will drop a small amount. This shrinking of the ball will make pressures higher in the low pressure state than they would be if the ball didn’t shrink so the constant-volume estimate of the temperature change required to account for the observed pressure drop will be a bit on the low side, unless the Carnegie experimentalists are correct and there is an offsetting increase in volume when the balls get wet.)
With fixed volume the general gas law becomes: P1/T1 = P2/T2
All of these numbers are known except for T1, the temperature of the air in the ball when it was first tested 2 hours before game-time. The known numbers just have to be converted from relative to absolute form.
First, the inflation pressures measurements are in pounds per square inch above atmospheric pressure, thus to get the full pressure inside a ball it is necessary to add atmospheric pressure (about 14.7 psi) to the measured psi.
Also, the gas law is based on degrees above absolute zero, which for Fahrenheit-sized degrees are “degrees Rankine,” which are Fahrenheit + 460. Solving for T1 in degrees Rankine:
T1 = (P1 x T2)/P2 = ((12.5 + 14.7) (50 + 460))/(10.5 + 14.7) = (27.2 x 510)/25.2 = 550.5°R = 90.5°F
Which rounds up to Professor Schmaltz’s 91°F.
Calculations for the Carnegie-Mellon experiment
In the Carnegie-Mellon experiment the expected post-equalization ball pressure, calculated just using the general gas law (where no gas is lost to condensation), is:
P2 = (P1 x T2)/T1 = [(12.5 + 14.7) x (50 + 460)]/(75 +460) = 25.9 psi
Subtract atmospheric pressure (14.7 psi) to get an expected pressure test reading of 11.2 psi, vs. actual experimental readings of 10.7 psi. The suggestion here is that the additional pressure drop found in the Carnegie experiment is a result of water vapor condensation.
If the Carnegie experimentalists were careful they would have compensated for the pressure drop that comes from energizing their pressure tester but game officials (who measured halftime pressure as 10.5 psi) might well not have taken this source of pressure loss into account. If they had the then the difference between their measured pressure drop of 2 psi and Carnegie’s measured drop of 1.8 psi might disappear.
Look at the Patriots fumble stats.
I figured that you of all people would have fun with that mangling of statistics. …If you cared.
how are the NFL footballs inflated? If the air is compressed immediately before inflating the ball (like with a manual bicycle pump), the temperature of the air inside the ball will be much higher initially. But if it’s inflated from an air tank that was pressurized hours ago to, say, 50 psi and was then allowed to cool, the air in the ball could be considerably colder than room temperature.
And what is the starting pressure of the balls? If They only need a little topping off, inflation won’t be changing the temperature.
A little off topic, but a good parody from a Seattle radio station KJR. Tom’s Big Balls http://www.sportsradiokjr.com/media/podcast-12th-manthems-12tmanthems/2014-week-18-toms-big-balls-25762269/
Go Seattle!
Wet leather stretches.
Anyway, in the future manufacture balls with pressure sensitive film and the ref can see with every play that they are properly inflated.
http://www.sensorexpert.com/tactile-surface-pressure-indicating-film.php
Maybe Bill Nye can give us the scientific explanation of how the pressure in the balls used by the Patriots caused the Colts to only score 7 points.
Perhaps they froze the balls and then inflated them. Regardless, we simply do not know enough details of the bizarre NFL rules and inspections to know IF there is simply a scientific explanation. This doesn’t even rank up there with wiping snot on a baseball. Time to move on.
One possibility that could contribute to the measured under-inflation is that the leather actually stretched under the applied internal pressure. After all, the footballs were brand new prior to inflating. If this is so, as the “brand new” leather stretches, the enclosed volume of air will increase, thus producing a “too low” pressure reading at a later time.
Some materials (e.g., polymers, leather) exhibit visco-elastic mechanical properties (i.e., time dependent properties). This means , over time, the leather will stretch at an ever decreasing rate under the applied internal pressure. In addition to just the leather stretching, one should also expect the football’s lacing to also “give” a little bit.
So, summing up, the lower temperatures plus the possibility of the brand new leather stretching could explain much of the pressure drop.
Of course, the Patriots could have just plain cheated.
Oh well, it was not a close game anyway.
Since the Patriots have stated that the ball pressure makes no noticeable difference in ball handling, the solution to the whole mess is easy. Just require the Patriots to play the superbowl with balls inflated to the same overpressure as the underpressure they used against the Colts. Shouldn’t cause them any problems at all.
The Pats only scored 17 points with the under-inflated balls during the first half. They went on to score 28 points after they switched to properly inflated balls, so it clearly worked against them.
http://www.wsj.com/articles/patriots-always-keep-a-tight-grip-on-the-ball-1422054846
By MICHAEL SALFINO
Updated Jan. 24, 2015 9:13 a.m. ET
One of the many questions surrounding “Deflategate”—the controversy that has engulfed the New England Patriots—concerns what advantage an NFL team would gain from using a deflated football. Numerous players have said a softer ball is easier to grip, and a ball that’s easier to grip is harder to drop
New England coach Bill Belichick and quarterback Tom Brady both denied ever purposely using footballs that were inflated below the NFL minimum. But on the basis of the allegations, the Count looked at the fumble rate of the Patriots compared with the rest of the league.
New England has had an uncanny ability to hold on to the football for quite some time. According to data compiled by Warren Sharp of Sharp Football Analysis, the Patriots fumble far less than any other team that plays outdoors, where the elements can make the football harder to handle. Beginning in the 2010 season, Patriots players have fumbled (whether lost or recovered) once every 73 touches from scrimmage, which is 52% better than the league average. The next best team is the Ravens, who have fumbled once every 55 touches.
Additionally, according to Stats, LLC, the six players who have played extensively for the Patriots and other teams in this span all fumbled far less frequently wearing the New England uniform. Including recovered fumbles, Danny Amendola, BenJarvus Green-Ellis, Danny Woodhead, Wes Welker, Brandon LaFell and LeGarrette Blount have lost the ball eight times in 1,482 touches for the Patriots since 2010, or once every 185.3 times. For their other teams, they fumbled 22 times in 1,701 touches (once every 77.3).
The Patriots didn’t return a request for comment.
Methinks it might be fear of Belichick as much as anything else.
I should add, if Patriots fumble fewer times (and they do) because of whatever… more power to ’em. There are an average of 2.3 fumbles per game, and if Patriots lead the league in the “1’s”, they are doing the NFL a favor by eliminating the spectacle of very large men doing a strange dance over downed opponents who have just turned over the football. All teams should be allowed to play with footballs deflated to their chosen psi!
Doesn’t compressing air heat it up? Maybe using a truck tire inflator v.s.a hand pump?
Numbers- we still don’t have no dag-gum numbers! 😉 What WAS the initial PSI? What WAS the final PSI? Was any pressure released when testing? How much? What was the ambient temp of the balls before going out to the field? Does Gronking have any effect on PSI? How much?
What was the starting PSI of the Colts’ footballs? What was their tested PSI?
And can someone tell the difference between 13.5, 12.5 and 11.5 PSI by handling the ball?
And what about chain of custody of the footballs? Also seeing that the Pats scored most of their points when using the Colts’ footballs I hear that Tom has contacted Andrew to find out what they do to their footballs… 🙂
12.5 psi before game, temperature unknown,
10.5 psi during game, temperature ~41F
The Colt’s ball tested around 12 psi at halftime.
If you feel closely, yes, you can tell. The refs removed several balls from play for being too soft over the course of the game.
The teams have their own sets of footballs that they use during their offense. They are kept by the team. Kickoff and field goal footballs are used once and only once fresh out of the box.
The 10.5 has been changed. The latest has the test pressure at 1 psi less than 12.5. And no. you cannot tell between 12.5 and 11.5.
It sounds to me like Coach Belichick use to follow NASCAR as a kid, or he got early training from ’em. ‘S t r e t c h i n g’ the rules is endemic there.
Someone get Al Gore to declare that the football pressure science is settled! Then we can determine who are football inflators and who are inflator deniers as soon as possible.
The fact that empirical (Carnegie Mellon) and basic physics (Ideal gas law) aren’t fully insync and that factors such as, humidity, ambient temp changes let alone, changes in barometric pressure, and thermal expansion/contraction of the material… If this simple problem has trouble being solved why would anyone think we got a good understanding of the climate?
You’ve all got it wrong, the balls were never under inflated.
It’s clear that the NFL hired NCDC to perform the pressure test procedure on the Pats balls.
We know their post measurement algorithm always adjusts 11 out of 12 raw data (locker room) measurements upwards, unfortunately for them the Mann applying the adjustments used them upside down…
we can’t resolve this issue because we don’t have the computer to model it
NFL Investigating Whether Patriots Played Game With Properly Inflated Vince Wilfork
Before reading this article, I had taken this website to be reputable. The facts are that all 24 footballs were filled with air pressure indoors and were again measured for air pressure indoors, at half time. The results were that 11 of the Patriots’ balls were found to be 2 to 3 psi bellow the minimum of 12.5 psig. One of the Patriots’ balls was not below specification and none of the 12 Colts’ balls were below specification. Just how could that have happened? Could the video of the Patriots’ locker room attendant taking all 24 balls into a bathroom just before game time, explain something? He was in there for 90 seconds and a New York reporter just posted a video today showing he could deflate 12 balls to the discovered values within 40 seconds.
Oh, I thought you were going to criticize WUWT for turning into a sports talk site.
You say “The results were that 11 of the Patriots’ balls were found to be 2 to 3 psi bellow the minimum of 12.5 psig.” Check out http://www.msn.com/en-us/sports/nfl/report-10-of-patriots-balls-only-one-pound-under-inflated/ar-AA8BCNy which leads to http://profootballtalk.nbcsports.com/2015/01/25/nfl-bears-plenty-of-blame-for-deflategate/ which says:
I’m sure the NFL will make things clear in their report, likely to be released on Feb 20, two days before the Daytona 500.
“The facts are that all 24 footballs were filled with air pressure indoors and were again measured for air pressure indoors, at half time.”
I have not heard any official word about the conditions under which the balls had their pressure measured either before the game or during halftime. If the balls were measured under the same conditions both times, it also needs to made clear to what extent the balls were allowed to come to equilibration with the environment (were the balls that had been used in the game permitted to warm back up before measurement, or was the air inside still cold). I also haven’t heard official word that the Colts’ balls were measured at halftime, but I assume that the officials would have done so out of due diligence.
“The results were that 11 of the Patriots’ balls were found to be 2 to 3 psi bellow the minimum of 12.5 psig”
An anonymous source stated via ESPN that 11 of 12 balls were found to be below the limit by as much as 2 PSI. Later reports (again anonymous) said that most of them were more like 1 PSI below the limit. Assuming these sources know what they are talking about and can be trusted, your statement is a gross exaggeration. Let’s wait for the official report on the pressure here.
“One of the Patriots’ balls was not below specification and none of the 12 Colts’ balls were below specification.”
The Colts have said that their balls are inflated to the max before the game, which means they could lose pressure and still be within the specs. The one Patriots ball could have stayed in the bag the entire half (and thus not gotten wet, which allows the leather to stretch), or it might have started out fuller, or it might have been blow the limit too (again, we have no official word on the pressures of any of the balls, just anonymous sources), or some combination of these possibilities.
“Could the video of the Patriots’ locker room attendant taking all 24 balls into a bathroom just before game time, explain something?”
It could explain that he thought it wise to empty his bladder before he became occupied with the came.
“He was in there for 90 seconds and a New York reporter just posted a video today showing he could deflate 12 balls to the discovered values within 40 seconds.”
I’m not going to post a video of it, but I can assume you that I can urinate, flush, and wash my hands within the allotted 90 seconds.
Really, let’s just wait for the official report before we start jumping to conclusions and attacking guys with weak bladders. If anyone in the Patriots’ organization was involved in willfully violating the rules, the league should come down hard on them, even if the advantage gained was miniscule or nonexistent. If it’s merely a result of the official pressure being taken 2 hours before the game, what reason is there to get all fired up?
The term “boyscout” is synonymous with the words honest and forthright. So a rule follower can be called a “boyscout”
Many fathers sign up their sons to join the organization called Boyscouts of America so that they can learn many practical lessons about nature and survival.
One of the most popular activities in Boyscouts is called the Pinewood Derby. In this derby the scout builds a pinewood racing car and competes with other scouts by racing the cars down a wooden track. The raw materials for each car are exactly the same. The rules are simple total weight has a limit. The question is “At what point in modification, weight placement, axle polishing, axle manipulation, graphite friction reduction does the Boyscout become a Cheater?” Understanding the physics of weight placement gives the scout the largest advantage and the best chances to win. Most of us would not consider a scout that learns and understands the physics and then applies it to his pinewood racer a cheat. Instead we would applaud them and other scouts would copy him as they too learned these lessons.
So why are we not applauding the New England Patriots for their understanding of the gas laws that gives QB Tom Brady the ever so slight advantage?
As usual, in a Pinewood derby some Dad’s get crazy. I saw one Dad put my little brother’s car at the top of the track, and press down so hard the axle’s bent. The little car had won the first race, but only wobbled halfway down the ramp during the next race.
Repeat after me: “It is only a game. It is only a game. It is only a game.”
The chart of vapor pressure of water versus temperature
http://www.pumpworld.com/vapor-pressure-chart.htm
indicates that at 90° F wet air would exert about 0.7 psi of pressure due to just the water vapor, but if cooled to 50° F the condensation would reduce that to less than 0.2 psi (about 0.18) – a ‘loss’ of over 0.5 psi just from condensation.
Anecdotally, this was obvious to me as a child. Footballs and basketballs kept in the house always felt inflated. Those kept in the garage “swelled” in the summer and “shrank” in the winter.
The duration of time it took wasn’t something I ever studied or cared about.
I may have missed a comment that covered this already, but another thing to consider is the temperature of the air leaving the pump. Due to the restriction of the tiny holes in the inflation needle the actual pressure in the pump (depending on how fast you pump) will be well in excess of the final pressure in the ball with the air expanding across the needle holes. There is almost no temperature drop for air in this type expansion, The temperature of the compressed air in the pump could easily be120°F.
http://www.popsci.com/science/article/2010-03/how-start-fire-just-compressed-air
“You’ve probably seen contestants on Survivor trying to make fire by rubbing sticks together or concentrating sunlight with their eyeglasses. But among preindustrial fire-starting methods, it’s hard to beat the portable convenience of fire pistons, used in Southeast Asia since prehistoric times.
“Almost all gases heat up when compressed. The harder and the faster the compression, the hotter the gas gets, hot enough even to ignite cotton wool or other flammable materials. Diesel engines work the same way: They have no spark plugs; instead the fuel/air mixture is ignited by compression as the cylinder closes up.”
I have found the answer to the question/issue. I seem to recall during the game a cam shot of the Gillette sky box. Therein lay the problem. Or solution as the case may be. Who other than the ever affable john’ f’n kohn-heinz-kerry was situated. The obvious lack of correct pressure was due to the overinflated ego that was present in close proximity to someones balls.
Nice scientific exercise. it doesn’t explain the reports of the balls magically reinflating to 12.5 psi after half time. I seem to remember that Luck went 12 for 33 passing and Blount rushed for 148 yards (71 more than the Colts) and scored 3 TD’s (2 more than the Colts).
No magic. The NFL has said they only used balls with the regulation pressure, and reports say that the underinflated balls were inflated to regulation by officials at that half-time. Brady did not seem to notice at all.
No magic. The NFL has said they only used balls with the regulation pressure in the second half, and reports say that the underinflated balls were inflated to regulation by officials at that half-time. Brady did not seem to notice at all.
So the score is 17-7 at the half. Then NE scores 4 tds in the second half with properly inflated balls? No scandal that I could see. New England did better with the properly inflated balls.
There is a global consensus that a football is not eggshaped but spherical.
And it is kicked, not thrown.
Y’all are missing the mystery. How did the Patriot’s balls lose air while the Colt’s balls did not? Theory smashed! Try again!
pbh
Maybe the Colts overinflated their game footballs and got lucky when conditions put them back within spec.
Each team’s balls had to be within specs when inspected. While I don’t doubt the science, I’m from Missouri and I know the smell of manure when I hear it. Both teams should have been equally affected by the same game conditions. Or perhaps the Colts kept their footballs in a warmer?
The fact of the matter is, the footballs were inflated to Tom Brady’s liking. Believe me, if the quarterback doesn’t like the condition of the football at game time, we’re going to hear about it.
That is already answered – knowing this problem and preferring a harder ball they inflated the ball in cold air or slightly over inflate it, knowing (it would be easy to experiment at different temperatures) roughly how much they would need to be inflated to fall within the rules when tested.
Compressing air causes the temperature of the air to rise significantly. This is why a lot of vehicles use intercoolers after the supercharger or turbocharger in order to reduce the air temp prior to combustion.