1. Air Pressure 5.4

2. 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)

3. 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 millibars.

4. 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.