This preview shows page 1. Sign up to view the full content.
Pressure
Atmospheric pressure
is the force per unit area that is always applied perpendicularly to a surface
by the surrounding gas. It is determined by a planet's gravitational force in combination with the
total mass of a column of gas above a location. Units of air pressure are based on the
internationallyrecognized
standard atmosphere
(atm), which is defined as 101,325
Pa
(or
1,013,250
dynes
per cm
2
).
The pressure of an atmospheric gas decreases with altitude due to the diminishing mass of gas
above each location. The height at which the pressure from an atmosphere declines by a factor of
e
' (an
irrational number
with a value of 2.71828.
.) is called the
scale height
and is denoted by H.
For an atmosphere with a uniform temperature, the scale height is proportional to the
temperature and inversely proportional to the mean
molecular mass
of dry air times the planet's
gravitational acceleration. For such a model atmosphere, the pressure declines exponentially with
increasing altitude. However, atmospheres are not uniform in temperature, so the exact
This is the end of the preview. Sign up
to
access the rest of the document.
This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.
 Fall '10
 EmilyHoward
 Astronomy

Click to edit the document details