Re: [Phys-L] physics and football

[John Denker <jsd@av8n.com>]

On 01/22/2015 06:44 PM, Paul Nord wrote:
> Moisture content of the air in the balls could change this
> dramatically also.  Wet air is not a very ideal gas.

That is something to consider, but I'm not sure it
qualifies as "dramatic".  Even saturated vapor pressure
at 22C is only 0.38 PSI, not enough to explain the
reported observations.

Y'all are overlooking the one thing that could do it:
The inflation process itself.

If you start with an uninflated football (1 Atm absolute
pressure) and inflate it at the last minute, I reckon
the absolute temperature goes up by 19% if everything
is isentropic and thermally insulated.  That means
it loses almost exactly 2 psi as it cools down.  Maybe
more if there's a little bit of friction somewhere.

It's an easy homework problem if you think about it
the right way.  PV^γ plus ideal gas law.  (It's a
horror show if you think about it the wrong way.)

Also note that the balls are presented for inspection
2 hours and 15 minutes before game time, so they have
plenty of time to cool off.
  http://static.nfl.com/static/content/public/image/rulebook/pdfs/5_2013_Ball.pdf

The trainer could swear "I inflated them to 12.501 and
never touched them after that."

===============

I resent the tone of the Jack Andrade article that 
cheating by means of physics isn't cheating.

I find it telling that the Boston Globe would get a 
Boston University professor to make excuses for the 
New England Patriots.  Sheesh.  I'm pretty sure a
Purdue professor wouldn't have made the same mistakes
... but science isn't supposed to work that way.
Scientists are supposed to get the right answer, 
no matter what their affiliation.

Maybe Senator Inhofe should hire Prof. Schmaltz to
do some climate "science".

It is also shameful the way Andrade suggests that it
is somehow the NFL's fault for not specifying the
temperature.  It should go without saying that the
responsible team is responsible for making sure the
ball complies with the rules /during the game/.

By way of analogy, there are federal inspectors who
make sure an airplane meets airworthiness regulations
on the day it is manufactured.  That does *NOT* mean
that the regulations do not apply on other days.  It
is the responsibility of the owner/operator to uphold
the regulations at all times during operation.

Gibbon spent 6000 pages arguing that the decline and
fall of the Roman empire was largely due to a lack
of "civic virtue".  It seems to me that cheating is
not a virtue.