1. Air Pressure

2. Elbow Chat What is weather? Describe the weather today.

3. Weather: condition of Earth’s atmosphere at a particular time and place. It can change day to day.

4. Elbow Chat Does air have mass? If so, how do you know?

5. Air has mass, which means it has “pressure”. Pressure: force pushing on an area

6. Elbow Chat 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?

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

8. Elbow Chat Observe the device that Mrs. Hood has at the front of the room. What do you think this is called? What do you think it is used for?

9. Barometer: tool used to measure air pressure AP drops – stormy AP rises – clear

10. Listen carefully to the following video. You and your elbow partner will have a few questions to answer at the end.

11. Elbow Chat on the Video (answer the questions on your paper in complete sentences) 1. What force is pulling air down? 2. Can the weight of air change? Explain. 3. In which type of temperature (hot or cold) do molecules move faster? 4. Which direction does cold air travel (up or down)? 5. Does temperature affect air pressure? Explain.

12. What force is pulling air down? Gravity

13. Can the weight of air change? Explain Yes. Hot air – lighter Cold air - heavier

14. In which type of temperature (hot or cold) do molecules move faster? Hot air

15. Which direction does cold air travel (up or down)? Sinks down

16. Does temperature affect air pressure? Explain. Yes. Hot air rises and cold air comes down to take its place. This makes the air move, which causes changes in weather.

17. 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.

18. AIR PRESSURE Pressure: 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.

19. 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.

20. 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.

21. 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.