air pressure at various height

For pressure in a liquid, the pressure

P = Po(pressure at liquid surface)+density*g*height

What about air pressure? Is there a similar formula for calculating air pressure at various and how to derive it?

Is there an air buoyant force acting on an object in air like the case immersed in a liquid?

thx

1 個解答

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  • 天同
    Lv 7
    8 年前
    最愛解答

    Atmospheric pressure various with altitude, because the temperature, and hence density, of air decreases with increase in height.

    A simple (but approximate) relationship between the air density with height is given by,

    p = (po).exp(-h/H)

    where p and po are the densities of air at height h and sea level respectively

    H is a constant which represents the mean height of the atmosphere

    Commonly accepted values for po and H are 1.21 kg/m^3 and 8000 m respectively

    Thus, the pressure P at height h is,

    P = integral { p.g.dh} with limit of integration from h to infinitiy

    where g is the acceleration due to gravity

    After integration, P = Hg(po).exp(-h/H)

    i.e. P = 8000 x 9.81 x 1.21 x exp(-h/8000)

    or P = 94960.exp(-h/8000) Pa

    This equation underestimates the actual atmospheric pressure as water vapour pressure has not been taken into account.

    A more accurate equation for atmospheris pressure at various altitudes is given in the following web-page,

    http://www.engineeringtoolbox.com/air-altitude-pre...

    Q:Is there an air buoyant force acting on an object in air like the case immersed in a liquid?

    The answer is YES. Archimedes Principle applies to fluids, which include both liquids and gases.

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