PV = nRT. It’s one of those laws you learned in high-school physics. For any gas, pressure x volume = number of molecules x temperature. The New England Patriots’ balls were tested in the Referee’s Room before the game. We don’t know the temperature, but 70°F = 20°C = 293.5°K is a good guess. The temperature dropped into the low 40’s (275°K or so) during the game. That’s a drop of about 6% from testing conditions, and so — you guessed — pressure would also drop by 6%. The Patriots say that they inflate the balls to 12.5 psi, the minimum allowable under the rules. That’s above ambient pressure of 15 psi, for a total of 15 + 12.5 = 27.5 psi. 6% of 27.5 is about 1.65 psi, so a drop in temperature alone explains a reading of 11.1 psi. ESPN reports the actual number as 11 psi, so that’s it. Physics did it.
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