[Tutor] Order Of Operations Question

[Hugo Arts]

On Wed, Jul 28, 2010 at 11:41 AM, David Hutto <smokefloat at gmail.com> wrote:
> 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
>

Either there is an error in the texts, or you have not checked
throughly enough. It goes wrong here:

>    """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

The Air pressure is in Pascal, which is kg / (m*s^2), not (kg * m)/s^2
as you state. That is the Newton. Pascal can also be written as
Newton/m^2, which is (M*g)/m^2. So to get mass per square meter, you
should divide by the acceleration g, not multiply.

With that modification I get about 5e18, which seems correct.

Hugo