1. Gas, Pressure, and Wind

2. Gases Recap - Nitrogen (78%), Oxygen (21%), Other and H2O (1%). Gases, like matter, have mass and are affected by gravity The gravitation pull causes atmospheric gases to be pulled toward the Earth. The weight of all the gases in the upper layers of the atmosphere presses down on each layer below

3. Atmospheric Pressure This weight compresses the gas molecules and increases the density of the air below Closer to the Earth, the air is more dense. More dense air exerts more force than less dense air Do you remember what force exerted on an area is called?

4. Atmospheric Pressure PRESSURE! The denser the air, the higher the force and pressure. Where do you think Atmospheric Pressure is the greatest? a.Troposphere b.Stratosphere c.Mesosphere d.Thermosphere

5. Atmospheric Pressure A. Troposphere! Just like air density, the air pressure is higher the closer you are to Earth. As a general rule - Atmospheric pressure is greatest near Earth’s surface and decreases as you move upward away from sea level This means there are more molecules of air close to earth and less up high.

6. How pressure looks

7. Atmospheric Pressure This is why some people find it hard to breath in high mountains It’s because the less air pressure = fewer molecules of air to breathe What are some experiences you have had with high or low air pressure? Think of times you have gone above sea level. Have you ever gone below? What happened?

8. Temperature, Weather, and Wind High pressure doesn’t just exist at higher altitudes. Temperature also affects air pressure Where air is heated, molecules move faster, so less of them are needed to fill a cubic centimeter of space than when air is cooler and molecules move slower Less molecules needed per cubic cm (as in hotter air) = less density or less pressure So hotter air = Lower Atmospheric Pressure

9. Temperature, Weather, and Wind These hot areas of air associated with low pressure and cold areas of air associated with high pressure affect weather. This is why we have pressure maps on our weather forecasts

10. Pressure Maps

11. Temperature, Weather, and Wind Remember how weather occurs in the troposphere? The sun heats the Earth and sends up warm air through the process of convection This sets up uneven heating in the atmosphere. This equals uneven pressures. Air moves from High Pressure to Low Pressure, creating WIND. Wind systems influence weather

12. Wind

13. Temperature, Weather, and wind When air gets warmer, it expands and rises! As the warm air rises, it reaches areas of less atmospheric pressure (less molecules of air… like in the diagram several slides earlier). The warm air molecules disperse to fill the spaces (expands). This results in a decrease in pressure because the molecules are more spread out. This also results in a decrease in temperature because there are not as many warm molecules per cubic cm as there were below.

14. Take a look again