I first solve the above equation for p2 and then plug in the numbers. So here is the corrected version of the calculation that you WUSA guy wanted to do (he wanted to calculate the pressure change for a temperature change from 68 to 51 degrees. You also do not have to convert to Pascals, that unit conversion drops out in p1/T1=p2/T2. you do the same calculation that you quoted but use 27 PSI instead of 12.5 PSI. (14.5 PSI) to the 12.5 PSI to get absolute pressure. On the other hand, theġ2.5 PSI that everyone quotes is “pressure above atmospheric pressure”.īut it’s easy to fix: you just add the value of atmospheric pressure When using the ideal gas law (which is where the formula p1/T1=p2/T2 comes from) you need to use absolute pressure. The calculation about the pressure change due to temperature change which you quote from WUSA is not quite right and it makes a difference. In the mailbag today, we received this correction to the calculations from Martin Schmaltz, a professor of physics at Boston University, who had also been mentioned in yesterday afternoon’s post. Neat! Look, we’re left with a solvable equation with one variable, p2, which is the pressure of the air inside the ball at game time! Let’s solve this riddle… But we also know the temperature on the field at the start of the game was reported as 51✯/10.6✬ (283.15 K). We convert psi (English) to pascals (Metric), which comes out to 86,184.5 Pa and assume room temperature (68✯/20✬) which converts to 293.15 K (Kelvin, the Metric equivalent). Let’s assume that each ball was inflated to the minimum pressure required to meet the NFL rules regarding proper inflation: 12.5 psi. Now, we can start solving this puzzle quite easily! For the same reason, n1 andn 2 can cancel. Since the volume will not change (assuming no air is added or taken away from the ball), then V1 = V2, and those can be cancelled. Where the 1 represents the initial readings and 2 represents the readings on the field. from when the balls were checked and the pressure, temperature, etc. Now, let’s just change the way the equation looks by moving all the letters to one side of the equation:įrom here, we need to think of this as two different times: the pressure, temperature, etc. We make the following assumptions, based on what we know about the procedure regarding regulation footballs in the NFL and about the Ideal Gas Law:ġ) V, the volume of gas (air) in the ball should not change, since (according to procedure), no air is added to or subtracted from the ball after reaching the proper inflation,Ģ) n will not change for the same reason as above,ģ) R does not change, since it is a universal constant. Yesterday, I posted a calculation from WUSA, which explained the Ideal Gas Law and how it applies to the question of whether the weather - specifically, the temperature - could be largely responsible for the fact 11 of 12 footballs used by the New England Patriots in Sunday’s win over the Indianapolis Colts were deflated. Honk if you predicted that an AFC Championship game would lead to a debate over the proper application of the Ideal Gas Law. Lots of media already in place for 9:30 Patriots press conference… /7LlgvCVlct
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