Chapter 1

The Atmosphere

Section 3

Air Pressure

Properties of Matter (Stuff)

• Mass, Volume, Density, and Pressure

• All of the matter in the universe has these properties, no matter how big or how small it may seem to us.

• We know how to find the mass, volume, and density of a solid and of a liquid… but what about air?

What About Air?• Does air have mass?

• Does air have volume?

How Do We Find Out If Air Has Mass and Volume?

Properties of Air

• Because air has mass and volume, we can find its density (the amount of mass in a given volume) by solving the density formula:

Density = mass/volumeD = m/v

Properties of Air

• The force pushing on an area or surface is known as pressure.

• A denser substance exerts more pressure than a less dense substance.

• Air pressure is the result of the weight of a column of air pushing down on an area.

Properties of Air

Measuring Air Pressure

• A barometer is an instrument that is used to measure changes in air pressure.

• There are two kinds of barometers: mercury barometers and aneroid barometers.

• The main difference between these two is that mercury barometers use liquid, while aneroid barometers use springs and levers.

Measuring Air Pressure

Increasing Altitude

• As you go higher into the atmosphere (increase in altitude), the amount of air above you gets less and less, so the air pressure decreases.

• Because there is less air taking up all that space in the upper parts of the atmosphere, the air density also decreases.

Increasing Altitude