# [Tutor] Order Of Operations Question

David Hutto smokefloat at gmail.com
Wed Jul 28 11:41:48 CEST 2010

```>From a practice exercise in Building Skills In Python page 64 I'm
working on How Much Does The Atmosphere Weigh? Part 1:
To check it states that the answer should be app. 10**18kg However,
and I've checked to make sure that the math I've layed out matches up
with the texts, I get 5.07360705863e+20

In the code I have broken the order of operations down to more
parenthetical, and tried outright, but see nothing obvious about how
it's strung together. If anyone has had a similar experience with the
problem given, or see anything blatantly obvious I've done wrong with
the ordering of operations. I tried to include as much of the
problem(formulas are just above variables they're used in) as comments
as possible.

import math
def atmosphereWeight():
pi = math.pi
"""Air Pressure (at sea level) P0. This is the long-term average.
P0 = 1.01325 × 10**5"""
airPressCLevl = 1.01325*(10**5)
gravity = 9.82
"""We can use g to get the kg of mass from the force of air
pressure P0. Apply the acceleration of gravity
(in m/sec2) to the air pressure (in kg · m/sec2). This result is
mass of the atmosphere in kilograms per
square meter (kg/m2).
Mm2 = P0 × g"""
masAtmoInKgPerSqM = airPressCLevl * gravity
"""Given the mass of air per square meter, we need to know how
many square meters of surface to apply
this mass to. Radius of Earth R in meters, m. This is an average
radius; our planet isn’t a perfect sphere.
R = 6.37 × 10"""
"""The area of a Sphere.
A = 4πr2"""
areaSphere = 4 * pi * (avgRadiusEarth**2)
"""Mass of atmosphere (in Kg) is the weight per square meter,
times the number of square meters
Ma = P0 × g × A"""
masEarthAtmoInKgPerSqM = airPressCLevl * gravity * areaSphere
print(masEarthAtmoInKgPerSqM)

atmosphereWeight()

TIA,
David
```