Wednesday, March 23, 2016

Casio fx-5800p: Barometric Formula

Casio fx-5800p: Barometric Formula

This program estimates the Barometric pressure at height H (given in meters).  This formula tends to work the best when H < 11000 m (approximately 36,089.24 feet).  


P = P0 * e^(-g * H * M / (R * T))

P0 = static pressure, 101,325 Pa
g = Earth's Gravity, 9.80665 m/s^2
M = molar mass of air, 0.0289644 kg/mol
R = universal gas constant, about 8.31432 N*m/(mol*K)*
T = standard temperature at sea level, 288.15 K (15 °C)

The value of R varies.  The constant stored in the fx-5800p is 8.314472.  Since this program uses values from built in constants, this value is used.  

Access to the Constants:
[ FUNCTION ], 4: CONST and then:

Gas Constant R:
down, down, down, 3

Earth's Gravity:
down four times, 3

Standard atmospheric pressure, labeled atm:
down four times, 8


For this text, constants are surrounded by single quotes (example: 'g')

"BEST UP TO 11000 M" ◢
'atm' * e^( -'g' * H * 0.0289644 ÷ ( 'R' * 288.15 )) → P

At 11,000 m, the pressure is estimated to be 27,500.16552 Pa.  

"Barometric Formula" Wikipedia Retrieved March 15, 2016

This blog is property of Edward Shore, 2016

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