Basic Assumptions
The gas which comprises an atmosphere is usually assumed to be an ideal gas, which is to say:
Where ρ is mass density, M is average molecular weight, P is pressure, T is temperature, and R is the ideal gas constant.
The gas is held in place by so called "hydrostatic" forces. That is to say, for a particular layer of gas at some altitude: the downward (towards the planet) force of its weight, the downward force exerted by pressure in the layer above it, and the upward force exerted by pressure in the layer below, all sum to zero. Mathematically this is:
Finally, these variables describing the system do not change with time; i.e. it is a static system.
Read more about this topic: Atmospheric Models
Famous quotes containing the words basic and/or assumptions:
“The basic thing nobody asks is why do people take drugs of any sort?... Why do we have these accessories to normal living to live? I mean, is there something wrong with society that’s making us so pressurized, that we cannot live without guarding ourselves against it?”
—John Lennon (1940–1980)
“All of the assumptions once made about a parent’s role have been undercut by the specialists. The psychiatric specialists, the psychological specialists, the educational specialists, all have mystified child development. They have fostered the idea that understanding children and promoting their intellectual well-being is too complex for mothers and requires the intervention of experts.”
—Elaine Heffner (20th century)