Air Pressure 5.4

Properties of Air Density: the amount of mass in a given volume of air. More molecules in a given volume, the density is greater. Less molecules in a given volume, the density is ___________? Pressure: force pushing on an area or surface. Air molecules push in all directions. (page 171)

Instruments that Measure Pressure Mercury Barometers – long glass tube that rests in a dish of mercury. When air pressure increases, it presses down on the surface of the mercury and forces column of mercury higher. Aneroid Barometers – Without liquid, when air pressure increases the thin walls of chamber are pushed in. Units of Air Pressure – Millibars, one inch of mercury is 33.86 millibars.

How does Altitude Affect Air Pressure and Density Air pressure decreases as altitude increases (as you go up a mountain, pressure decreases) Altitude affects Density-As you go up the density of the air decreases because the gas molecules are farther apart. This is why you become short of breath at a higher altitude.