1. Air Pressure & Density in the Atmosphere
7.E.1.1. NC Essential Standard: Compare the composition, properties, and structure of Earth’s atmosphere to include mixtures of gases and differences in temperature and pressure within layers.

2. Density Density: the amount of mass in a given volume of substance.
Imagine a bowling ball and a soccer ball are the same size. Which has a higher density?

3. DENSITY = The number of molecules in a given volume.
Air density decreases with increasing altitude
due to gravity.

4. What is atmospheric pressure??
As you increase in altitude, or distance above sea level, the atmosphere becomes less dense (“thin air”), meaning there is less atmospheric pressure.
What is atmospheric pressure??

5. ATMOSPHERIC PRESSURE = The force of the air weighing down over a
unit of area.
- Air pressure decreases
with altitude.

6. Atmospheric Pressure
Air molecules constantly bounce off each other and push on all the surfaces they touch.
The amount of pressure exerted by our atmosphere is about 14.7 pounds per square inch.
Why don’t you feel it?
All the air and liquids in your body push outward with the same pressure!

7. WEATHER
- Air pressure can also tell us about what kind of weather we might have.
HIGH pressure: clear skies + cooler temperature
LOW pressure: storms & rain + warmer temp.

8. WIND!!!
- Wind is caused by air flowing from high pressure to low pressure.
- Uneven heating of Earth’s surface causes pressure differences which sets air in motion.

9. = any instrument that measures air pressure.
Barometer
= any instrument that measures air pressure.
The flexible chamber on the barometer contracts when the air pressure increases and expands when air pressure decreases.

10. Expand & Contract
When air gets hot the molecules move away from each other – they EXPAND.
When air cools down the molecules move closer together – they CONTRACT.
How could we test this?

11. Air Pressure and Density