On Wed, Jul 28, 2010 at 6:19 AM, Hugo Arts <hugo.yo...@gmail.com> wrote: > On Wed, Jul 28, 2010 at 11:41 AM, David Hutto <smokefl...@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.
In the initial email I did forget this part: Pressure is measured in Newtons, N, kg m/sec2. Air Pressure is is measured in Newtons of force per square meter, N/m2. Which might have been a more informed question. I was trying not to add in the whole question, and place the pieces in, but apparently forgot one. > > With that modification I get about 5e18, which seems correct. I get this with yours and Evert's modification from mult to div, but if you're right, then the 10e18 the book states as a checker is a typo/error. Thanks, for your replies, I'll redo the example again, with a little more sleep this time. Don't really need to know atmospheric pressure right now, but might endup at wikipedia/google later. > > Hugo > _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
