Quote of the day: Patriots deflated balls? Post on the NFLs explanation about their actions on INFLATEGATE. I was actually wondering about this myself. This is pretty cool. danyod says: Jan 23, 2015 1:49 PM The effect of temperature on football inflation. Assume that the game footballs were inflated in a 75 F degree locker room, then taken out to a playing field at a temperature of 50 degrees F. How much would the change in temperature decrease the pressure in the football? High school physics tells us that the ideal gas law PV=nRT applies. That is, pressure times volume is equal to the number of moles times the gas constant times the temperature of the gas (in degrees Kelvin). Thus, given a constant amount of air in the football and a negligible volume change, the pressure will obey: P = nRT/V The change in pressure is thus proportional to the change in temperature, The 75 degree locker room has an absolute temperature of 297o K The 40 degree playing field has an absolute temperature of 283o K The change in temperature of 14o K will thus cause a drop in pressure of 14/297 = 4.7%. To translate this into a pressure change we must recall that football pressure is measured in gauge pressure, relative to the atmospheric pressure of 15 psi. So the absolute pressure within a football pumped to 13 psi is 13 +15 = 28psi absolute. The 4.7% drop applied to the absolute pressure gives a drop of 1.32 psi. Thus, the pressure within the football at game time will be only 13 -1.32 = 11.68 psi and thus well below regulation gauge pressure of 12.5-13.5psi. If they were just at 12.5psi to start they would be down by 1.3psi to 11.2psi by game time. And of course, a little pressure is lost every time you stick a needle in to check the pressure. Some guy on TV did this calculation but I think he forgot about absolute pressure vs gauge pressure and underestimated it. It thus seems highly likely that the Patriots equipment manager checked all 12 balls in a warm locker room and they lost pressure merely by cooling off on the field. In addition, the cold rain would have accelerated the heat transfer out of the balls. Finally, if the indoor inflation air was very humid, there would be an additional loss of pressure due to water vapor condensation on the inside of the bladder as the temperature of the football dropped.
Posted on: Fri, 23 Jan 2015 21:56:23 +0000
Trending Topics
Recently Viewed Topics
© 2015