Introduction

• Is defined as the force exerted by the air column above any given place
• The atmospheric pressure of any given place is defined as the force exerted upon a given surface by the air column above it. Thus, mass of the column of air above the given point determine the atmospheric pressure at that point.
• At sea level, 1 atm pressure

=1034 gm/cm2

=760mm of Hg

=1013.25 mbar

= 1.01325 bar

= 101.3 kPa

= 14.696 psi (lbf/in2)

Gas Law

The equation showing the relationship between pressure, volume, temperature and density of the gases is called gas laws. Some of the relevant gas laws are;

a) Boyle’s Law: At constant temperature the volume of gas is inversely proportional to the pressure on it. P1V1 = P2V2; V1 = the initial volumeV2= the final volume P1= the initial pressureP2= the final pressure

b) Charles’s Law states that the volume of a gas will vary directly with the absolute temperature, given that the mass and pressure remain constant. V1/T1 = V2/ T2

c) Gay Lussac’s Law states that if the volume and the mass remain constant, the pressure exerted by a gas varies directly with the absolute temperature of that gas.

d) Ideal Gas Law: Air can approximately be regarded as an “ideal gas” ideal gases obey the “ideal gas law”: P = C.r.T, Where P = pressure exerted by the gas; C = constant, r = density of the gas = mass/volume; T = Temperature of the gas