1. Mrs. Wharton’s Science Class

2.  Air consists of atoms and molecules therefore it has mass.  Because air has mass it also have other properties such as density and pressure.  Air has weight  Air molecules are in constant motion and are affected by gravity.  The force of this motion causes air pressure.

3.  Density- the amount of mass in a given volume of air.  Pressure- the force pushing on an area or surface.  Air Pressure- is the result of weight of a column of air pushing down on an area.  The molecules in air push in all directions so it does not crush objects.

4.  Air pressure varies slightly over the earth’s surface, and variations are responsible for the weather.  Low pressure is associated with storms, tornadoes and hurricanes  High pressure is associated with clear and dry conditions.

5.  Air pressure changes with elevation  As you move up into the atmosphere, the air molecules are further apart  As you move down into the atmosphere, the air molecules move closer together.

6.  Barometer - an instrument that is used to measure air pressure  Mercury Barometer- glass tube partially filled with mercury.  Aneroid Barometer- most used in homes.

7.  As altitude increases air pressure decreases  As altitude decreases air pressure increases  As pressure decreases, density decreases  As pressure increases, density increases