It is assumed that the pressure value is the difference in pressure between the measurement point and the top of the fluid. fresh water = 1)Įnter the pressure reading measured at the base of the fluid column. ρ 0 = Density of fresh water (1000 kgm -3 SG = Specific gravity of liquid (e.g.The calculation formulas used for this tool are: This calculator and conversion scale is used to determine the height of a column of liquid from the pressure generated at the bottom of the liquid column and show a custom pressure to liquid depth conversion scale. Fluid depth to hydrostatic pressure calculator.Pressure to diesel fuel level conversion.Questions/Comments? email me: schmaltz(at) physics. This effect can be bounded by 0.3 PSI (this is what I get if I assume that the air was 100% humid at 75F and all of the water condenses out), but it is negligible if highy compressed and dry air was used for inflating the balls (as opposed to a hand pump which does inflate with moist air). Humid air could lead to a further reduction in the pressure as the ball cools down because condensation of water inside the ball would remove gas from the football. (d) Humidity: The calculator also assumes that the air in the football is dry. I have calculated this additional change to be about +0.05 PSI (see plot created with local barometric pressure data provided by Bob Hayes). This only has a very small effect which would have increased the measured ball pressure at half time. (c) Barometric pressure - the weather: It also ignores the effects of the barometric pressure change that night in Foxboro. This is a negligible effect if the air of the environment is very humid (as it was). Wet balls are slightly cooler than dry balls due to evaporative cooling. Immediately after inflation the temperature inside the football can be higher or lower than room temperature, depending on how it was inflated. (b) Temperature equilibration with environment: It also assumes that that the temperature of the air in the football has time to equilibrate with the temperature of the environment.Ī reader of this page told me that he experimentally found this to take about 30 minutes (by sticking the ball in a fridge and monitoring the pressure change in the ball). This effect is very difficult to estimate as it depends on the detailed properties of the leather used. The leather case of the football probably stretches slightly when it get wet, this would increase the volume and result in a further reduction of the pressure. (a) Volume change: This assumes that the volume of the football did not change significantly due to the change in pressure. The calculator does this for you automatically. It is a very common error to forget to add atmospheric pressure to gauge pressure to obtain absolute pressure. The formula used in the calculator is Pf=Pi*Tf/Ti where T and P are absolute temperature and absolute pressure. The defaults are my best guess for what might be realistic values. inside a referee's locker room) to a final temperature (e.g. Of a football as it is taken from an initial temperature (e.g. This calculator uses the ideal gas law to compute the change in internal pressure Martin Schmaltz' pressure calculator pressure calculator
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