The low-level cold I've been nursing for a month now finally exploded into the full unpleasantness of my usual winter illness Saturday, or else I would've been more active following up on my Deflategate article and my ideal gas law post. As it was, for most of the day, I could barely keep on top of clearing comments from moderation.
Anyway, a few things deserve more prominent responses than a comment at the end of a long post, so:
-- I was in bed during the great Bill Belichick press conference, though I saw some mockery of it come across Twitter. While it may not have played well with the sports media, I do applaud the Patriots for doing a bit of science, here. Good for them, and the sports media can pound sand.
-- Their story seems to be that right before they fill the balls, they do... something to the outside that tends to raise the pressure. It's described as "scuffing up," but for all I know involves a belt sander. Anyway, the balls are filled to the low end of the legal limit right after this mystery procedure, then the pressure drops as they settle down, ending up below the legal limit some time later. And cold weather will tend to enhance that.
And, you know, it might be the cold pills, but I kind of buy that. It's mostly consistent with what we know, and would fit their organizational profile of walking right up to the edge of what's allowed by the rules. It would suggest that they've been preparing balls that were technically illegal for a long time, and it's just that this time somebody in power noticed.
-- I do mostly agree with several people who have said that this would be a non-story if it didn't involve the Patriots. That's not quite true-- if it involved the Cowboys, say, I think it would also be a huge story. But, yeah, the Patriots and their image are a big issue, here. But then, you get what you pay for. They've worked really hard, often right at the edge of the rules, to lift themselves up from an afterthought to one of the most prominent franchises in the sport, which is great. This sort of overdone scrutiny is the down side of that transformation, and an inescapable part of success.
It really is a pretty silly story, though, and without the physics angle, I probably would've just rolled my eyes and moved along.
-- A couple of other tidbits from that article about the press conference are interesting, chiefly this paragraph:
In a statement Friday, the NFL confirmed reports that multiple footballs used in the first half by the Patriots fell below the range of 12.5 to 13.5 pounds per square inch. The Patriots led at halftime, 17-7. Playing the second half with footballs that were measured — both before and after the half — as conforming, the Patriots outscored the Colts, 28-0.
The "both before and after" speaks to one of the more common alternate explanations, namely that the balls getting knocked around in the course of the game would lead to some sort of pressure change. If they checked the balls at the end of the game and found pressures in the same range as after the halftime re-inflation, that would tend to indicate that there's no significant usage effect. Which doesn't surprise me-- football is largely a game of standing around waiting for the next play to start, and they rotate balls fairly often-- but it's nice to have a bit of second-hand confirmation.
-- Regarding the questions about my experiment, it looks like the pressure sensor I was using measures absolute pressure, not gauge pressure, which is why the results fit the ideal gas law so nicely. I'm not sure exactly how it does that (internal barometer? adding 14 psi to everything?); I just grabbed it off the shelf and plugged it into the computer.
There have been a lot of claims made about this being due to non-ideal-gas behavior of one sort or another, none of which I buy. The ideal gas law was originally developed in experiments in just this sort of range of pressures and temperatures-- if there were significant deviations from it for pressures not all that much above atmospheric pressure and temperatures where water is a liquid, thermodynamics would be very different.
There have also been repeated calls-slash-demands for me to re-do the tests, which I won't be doing because I have a day job (and the aforementioned nasty cold). I've already put off a bunch of paper grading longer than I should've on account of this whole business (admittedly, it isn't hard to get me to put off grading...). I'm satisfied that I understand what's going on, over a range of temperatures that spans those relevant to the game (data points at 20C and 1C), so I'm moving on to the next thing.
-- Finally, as to rooting interests: The Conversation has a "disclosures" section, and I thought of adding a humorous note about my football fandom. I decided not to, as I didn't know how that would be received by that audience. For the record, though, I'm a Giants fan married to a Patriots fan (yes, that's led to some awkward moments, none worse than watching the Giants beat the Pats from the delivery room at the hospital when The Pip was born...). Some gentle snark aside, I've always liked Bill Belichick, back to his days helping my Giants win a couple of Super Bowls under Bill Parcells.
A week from now, if I managed to watch the game at all (not a sure thing, given two cartoon-mad kids in the house), I'll be rooting for New England (it helps that I find the Seahawks hard to like...). That doesn't stop me from rolling my eyes a little at their approach to NFL rules, though...
And that is probably just about enough on this whole weird story.
Re: Giant Fans and Patriot Fans. My niece and nephews were raised to be Yankee and Giant fans despite living in New England. My niece married a Red Sox fan and seems to have converted to the darker side (at least on football). One nephew was driving home from a Super Bowl party after Eli and the Giants triumphed over Tom and the Patriots. There was a stony silence in the car when someone telephoned and his phone played the Giants fight song.
Yeah, one of Kate's relatives is a lifelong New Englander, but roots for the Giants because that's what people in New England did before the Patriots existed. That's easier to swing, though, because they play in different conferences-- I don't know how you'd survive as a Yankee fan north and east of Connecticut...
What about this experiment? https://www.youtube.com/watch?v=_Gd0kGhIcF4 Also, although gauge vs. absolute pressure would be an issue in predicting pressure change due to temperature change, I'm pretty sure you want to do the experiment using gauge pressure because that's what the ref's would have been using. Finally, it's curious that nobody talks about the pressure of the balls the Colts were using - did anybody measure them at halftime? Because they would make an interesting control data point. Ideally all of the balls used in the game would have been measured before, during, and after the game, and then it would have been evident if any balls had been tampered with or damaged. Very frustrating that we don't have that data.
Their story seems to be that right before they fill the balls, they do… something to the outside that tends to raise the pressure. It’s described as “scuffing up,” but for all I know involves a belt sander. Anyway, the balls are filled to the low end of the legal limit right after this mystery procedure, then the pressure drops as they settle down, ending up below the legal limit some time later.
I don't see how you can possibly buy that unless you assume their "scuffing up" procedure warms up the balls substantially.
The rule of thumb derived from the Ideal Gas Law is that a 20 degree F temperature drop will result in a 1 psi pressure drop. Thus, since the outside temperature was about 20 degrees less than room temperature, it's hard to see how the weather alone could account for the reported 2 psi pressure drop. But Belichick basically spilled the beans: he said that their scuffing procedure somehow affected the inside of the ball raising the pressure by 1 psi. That was pretty disingenuous IMHO: when asked if he consulted with any scientists, Belichick didn't deny it. Of course, we know that raising the pressure by 1 psi entails raising the internal temperature by 20 degrees. Also, it intuitively seems like it would take a lot of friction to raise the temperature from 70 to 90 degrees. Now, Belichick didn't exactly say they scuffed them right before handing them off to the officials who set the pressure to 12.5 psi. But the 1 psi increase because of the 20 degree heating would nicely explain the 2 psi pressure drop. So that's what they were doing IMO: giving heated balls to the refs. Simply fill the ball to 13 psi, heat it up somehow (heat lamp, hot tub, microwave) until the pressure gets to 14 psi, run it over to the refs who then set the pressure to 12.5 psi, and voila, you got a 10.5 psi ball at game time. Note that this procedure does not violate the letter of the law! ;-)
#4: The only other option would be something chemical, that temporarily drives some component of the lining of the balls into a vapor that then condenses back onto the lining. That's a little hard to picture, though, so I bet they're heating the balls, either directly or mechanically (scuffing them up by tumbling them in a clothes dryer with something rough, would be my guess...). Belichick claimed they weren't heating them, but wouldn't give details of the process.
The thing is, IIRC, Belichick didn't deny they were heating the balls. In fact, he didn't say one single lie in that entire press conference IMHO. He said enough scuffing can raise the pressure by 1 psi. That's not a lie. He denied inflating the balls in an extra hot room. But then again, you don't have to be a hot room to heat up something. He said they didn't violate one letter of the NFL rules. But there's no rule that says you can't heat up the balls before submitting it to inspection! He said they didn't violate the integrity of the sport. But as long as you're staying within the letter of the law, who's to say you're violating the integrity of the sport no matter what other trick in the book you employ? I hate to admit it, but I kinda admire the guy--this is why he's best coach in the league. The Broncos could have taken a page or two out of his playbook--Manning was always butterfingers in cold weather. ;-)
Heating the balls would make some difference to the air temperature inside the balls at the time they were filled. Think of pouring a beer into a hot glass. But now you have a hot ball that you need to give to the refs to measure before both the ball and the air inside it cools down and the pressure drops. Wouldn't the tester notice that the ball is toasty?
A much better way to avoid detection would be to cool the ball down, and fill it up with hot air, then hand it to the refs For testing.
What if you took a cold deflated ball out of the fridge (approx 35 degrees), and put a hair dryer (maybe 140 degrees) to the air inlet of the air pump. Fill the ball up to 135 psi and wait for the ball temperature to come up to around 50 degrees so that it is not noticeably cold, but the air inside is still hot (maybe 130 degrees) to give it to the refs to measure (maybe 13 psi on the nose). By game time 2 hours and 15 minutes later, the air has cooled to ambiant, the ball temperature is at ambiant, and the pressure has dropped (maybe to 10.5 psi).
It would be interesting to have someone do this experiment.
Chad, I'm not following you when say "It would suggest that they've been preparing balls that were technically illegal for a long time." In what way are they "illegal"? They measure within the tolerable range at the appointed time - that's the rule. In fact, it would be closer to the truth to say "they've been preparing balls that were technically *legal* for a long time".
Even if you put hot air inside the ball, unless you heat the ball itself, it will very rapidly equilibrate to a temperature not all that far above the temperature of the exterior, because the ball itself has a mass tens of times greater than that of the air, and probably a higher heat capacity as well. There's just not enough heat energy in the air to significantly raise the temperature of the ball, and I'd expect the equilibration to be pretty fast.
Warren Platts nailed it. Of course the Patriots are heating their footballs before they are inspected! The only way to get the 1 psi rise in pressure that Belichick claims their "conditioning" causes is through heat. Whether it is from a belt sander or a hair dryer, the point is the balls are warm when the officials measure the pressure to be at the minimum of the spec. A 90 degree ball at initial inspection would completely explain all the measurements.
This is also explains how consistent the 2 psi loss reportedly was. It's hard to believe that a ball boy sticking a needle into the fill valve could deflate them so consistently.
The rule only states that the ball pressure must be between 12.5 and 13.5 psi when it is measured. It doesn't specify what temperature the ball should be at the time. From a scientific standpoint, the rule is inadequate. I expect no penalty for the Patriots, because they didn't violate any rules. But next year, the NFL with modify ball rule to say something like the balls have to sit in the room for an hour at 70F before they are measured.
If you're going to modify the rules, the rule should be that the balls sit at and are measure in something close to field conditions-- in a sheltered area on the sideline, or whatever. That's what matters, after all.
Chad: they could do that and it makes some sense. However, presumably the teams would prefer to fill and condition their footballs indoors. So they would have to inflate to a different indoor pressure for each game, depending on the weather. They would have to hire a physics nerd with a calculator (or Bill Belichick) to figure out what the initial pressure should be. For the ball to be in-spec in "Ice-bowl" type conditions, it would have to be overinflated by 3 psi initially.
Or maybe just widen the standard: If a QB prefers a 10 psi ball instead of a 12.5 psi ball, what's the big deal as long as it's not a complete Nerf ball?
would inflating with something other than air make a difference? I know with bikes, that CO2 inflated tires lose pressure much more quickly than ones inflated with air.
Along the Patriot vs. Giants lines - One of my aunts (and possibly one uncle) is a Yankee's fan despite growing up in Pawtucket, living most of her life in Pawtucket, and now living on the Cape. It's almost enough to disown her.
My father (also RI native) is a big baseball fan in general but I can't remember him being a particular fan of any team oddly. Football is another story - Patriots, even through the rough years and he hates the Redskins. I don't know who my Dad favored before the Pats existed but he's never been a Jet's fan.
With all the commercial breaks, the refs have plenty of time to check the ball in play and fill it up as needed. If ball pressure is such a big deal, why aren't they doing this?
Few people have been discussing the fact that the balls were wet because of the soaking rain. Was there any wind? The right combination of a wet football and wind could lower the temperature even more. That, along with the increase in temperature from scuffing might be enough to account for the 2 psi delta. Chad, did you do any tests to account for the wet balls?
"... it looks like the pressure sensor I was using measures absolute pressure, not gauge pressure, which is why the results fit the ideal gas law so nicely. I’m not sure exactly how it does that (internal barometer? adding 14 psi to everything?)"
Absolute sensors have a vacuum and/or are sealed on the "back side" of the sensing element (e.g. some form of diaphragm). Gauge sensors are vented to atmosphere. The absolute sensor will show barometric/altitude changes, and the gauge sensor shows pressure relative to atmospheric.
Update. Only one ball down two psi and the rest a few ticks below? Brady and the refs may not have even touched that ball that was under by two psi. If this is true, the media and former players who have commented on calling Brady and the Patriots should be embarrassed about commenting without any facts. With eleven balls only a few ticks below the min allowable psi, that would explain why Brady, the refs AND the Colts player didn't notice anything different in the balls being used in the first half