NFL Rules & Regulations on Inflation of Game Balls

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Doubting Thomas
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NFL Rules & Regulations on Inflation of Game Balls

Post by Doubting Thomas » Thu Jan 22, 2015 6:28 pm

Are there any physics experts than might know if changes in ambient temperatures could determine the inflation of a football?

http://heavy.com/sports/2015/01/rules-p ... -pressure/" onclick="window.open(this.href);return false;
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Austin Harper
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Re: NFL Rules & Regulations on Inflation of Game Balls

Post by Austin Harper » Thu Jan 22, 2015 7:49 pm

Well the Ideal Gas Law says pV = nRT
where p is pressure, V is volume, n is the number of moles of gas, R is the ideal gas constant, and T is the temperature of the gas. So if we assume the volume of the ball remains constant, and no gas leaks out (n remains constant), if we decrease T then p will also decrease.

Remember that the temperature is on the absolut scale so a change from 75°F to 65°F (297 K to 291 K) would only decrease the volume by 297/291 = 2%. It looks like the pressure of a football is supposed to be 13 psi and theirs were 11 psi. These are also gage pressures, but let's assume we're measuring at sea level (14.7 psi) so the difference is (13+14.7)/(11+14.7) = 8%. To decrease the pressure by 8% you would have to go from 75°F to 35°F (275 K).
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thinwhiteduke29
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Re: NFL Rules & Regulations on Inflation of Game Balls

Post by thinwhiteduke29 » Tue Mar 24, 2015 9:13 pm

it was a made up story from the get go. It never happened