AIR PRESSUREChapter 15 Section 2

Goals

Identify some properties of air.

Name instruments that are used to measure air pressure.

Explain how increasing altitude affects air pressure and density.

What We Know! How many of you have ever

been on an airplane? Did your ears pop? Why do you think that is? (turn

and talk)

Properties of Air Because air has mass, it also has other

properties, including density and pressure. Density- the amount of mass in a

given volume of air Density= Mass/Volume

Pressure- the force pushing on an area or surface.

Air Pressure- the result of the weight of a column of air pushing down on an area.

How are mass and air pressure related?

Air Pressure Turn to page 517. The atmosphere is

HEAVY. The weight of the column of air above your desk is the same as the weight of a large school bus!

Why do you think it doesn’t crush us?

Measuring Air Pressure

Barometer- an instrument used to measure air pressure. Two types of barometer include mercury

and aneroid barometers.

Mercury Barometer Consists of a glass tube open at the

bottom and partially filled with mercury.

The space in the tube above the mercury is almost a vacuum.

As air pressure pushes down, the mercury level goes up!

Aneroid Barometer Contains an air

tight metal chamber. When air pressure increases, the chamber walls are pushed in.

As the air pressure changes, the needle moves.

Altitude and Properties of Air At the top of a

mountain, the air pressure is less than at sea level.

Air pressure decreases as altitude increases.

As air pressure decreases, so does density.

Altitude-elevation