Air Pressure

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• What is weather?

• Describe the weather today.

• Weather: condition of Earth’s atmosphere at a particular time and place.

• It can change day to day.

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• Does air have mass?

• If so, how do you know?

• Air has mass, which means it has “pressure”.

• Pressure: force pushing on an area

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• The weight of the column of air above your desk is about the same as the weight of an

entire school bus!

• Why does it not crush us?

• Air molecules push in all directions, not just down on us. So the pressure evens out.

• Barometer: tool used to measure air pressure

• AP drops – stormy

• AP rises – clear

PROPERTIES OF AIR

• Air has mass.

• Density: the amount of mass in a given volume (space)

• Formula: D = M/V

• If there are more molecules in a given volume of air, the density is higher. If there are fewer molecules, the density is lower.

AIR PRESSUREPressure: Force pushing on an area or surface

• Denser air exerts more pressure than less dense air.

• Air pressure:

• Definition: result of a weight of air pushing down

• Why does air pressure not crush us?

It is pushing in ALL directions, so it evens out.

MEASURING AIR PRESSURE

• Falling air pressure means stormy weather is coming.

• Rising air pressure means fair/good weather is coming

• Barometer is the tool used to measure CHANGE in air pressure.

INCREASING ALTITUDE• Altitude

Definition: distance above sea level

As altitude increases, air pressure and density decreases.

Air pressure is greatest at sea level.

Air at the top of the atmosphere has lower air pressure.

Altitude affects density

*As you go up through the atmosphere, air pressure decreases.

As air pressure decreases, the density of air decreases.

• Why is it harder to breath at higher altitudes?

Air is less dense because the air is spread out. This means fewer oxygen molecules to breath in.