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:
“Not many appreciate the ultimate power and potential usefulness of basic knowledge accumulated by obscure, unseen investigators who, in a lifetime of intensive study, may never see any practical use for their findings but who go on seeking answers to the unknown without thought of financial or practical gain.”
—Eugenie Clark (b. 1922)
“Assumptions of male superiority are as widespread and deep rooted and every bit as crippling to the woman as the assumptions of white supremacy are to the Negro.... this is no more a man’s world than it is a white world.”
—Student Non-Violent Coordinating Committee, African American civil rights organization. SNCC Position Paper (Women in the Movement)