1. Agenda Today’s Focus: Air Pressure CA Content Standard: 6.4.e Students know differences in air pressure, heat, air movement, and humidity result in changes in weather. Objectives: 1. Students will be able to reproduce the formula for pressure 2. Students will be able to identify how atmospheric pressure changes with elevation Outline: What is pressure? What is atmospheric pressure? What’s the relationship of pressure & elevation?

2. 1. Does air have mass? (263) Yes. It may seem to you that air has no mass. But in fact, air consists (is made up)of atoms and molecules, which have mass. 2. Key Concept: Because air has mass, it also has density and pressure.

3. 3. What is density? (page 263) Density is a measure of how much mass there is in a volume of a substance. “For example, rock is more dense than water because a given volume of rock has more mass than the same volume of water.” Hypothesize how we can test that this is true.

4. 4. How can you calculate the density of a substance? (263) Density = Mass Volume Let’s practice: What is the density of a billiard ball that has a volume of 100 cm 3 and a mass of 250 grams?

5. This man is getting crushed! This man is getting stepped on! Why were these guys not worried? Hint: It’s the same reason we should not be worried about the weight of air pressure pressing down on us each day. PRESSURE!!

6. Pressure is the force pushing on an area or surface. Can you name some familiar forces acting on you right now that create pressure? FORCE AREA PRESSURE FORCE AREA = gravity (your weight)‏ weight of the air (air pressure)‏ 5. What is pressure? (263)

7. Air pressure is the result of the weight of a column of air pushing down on an area. Hundreds of kilometers Area = 1 m 2 column of air How much does this column of air weigh? 11.5 tons! The equivalent of a bus. Force (weight) PRESSURE FORCE AREA = 6. What is atmospheric (air) pressure? What force causes air pressure?GRAVITY!

8. 7. The weight of the column of air above you right now is the equivalent of a school bus. Air exerts its force in all directions- down, up, and sideways. The air pressure inside our bodies is the same as the air pressure outside of our bodies; these pressures balance, which ensures that we don’t get crushed. So why aren’t you being crushed? Toonpool.com

9. Let’s return to the bed of nails… here’s why those guys didn’t need to worry! FORCE AREA FORCE AREA PRESSURE FORCE AREA = PRESSURE FORCE AREA = BOOM! Because the force is divided into a larger area on the bed of nails, the pressure on the balloon is smaller than with the single nail. bed of nails single nail

10. 8. What is a barometer? A barometer is an instrument that is used to measure air pressure. Air pressure pushes down on the mercury in the reservoir which pushes mercury up the glass tube. Atmospheric pressure = height of mercury in tube measured in inches or millibars height = pressure

11. 9. Use page 264-265 to compare at least two similarities and two differences between a mercury barometer and an aneroid barometer. Mercury Barometer Aneroid Barometer

12. 10. What is the relationship between elevation and air pressure? (p. 265)

13. 10. What is the relationship between elevation and air pressure? (265) As the elevation increases, the air pressure decreases. The higher the elevation, the lower the air pressure.

14. 11. In which layer of the atmosphere does the air pressure change the most? The troposphere

15. 12. What is the air pressure when the elevation is zero? (standard air pressure) 1013.2 mb

16. 13. Why does air pressure change with elevation? (265-266) At higher elevations, there are fewer air molecules to cause the air pressure.

17. As elevation increases, the number of molecules of air in a certain volume decreases elevation At higher elevation, less air above you, less weight (force), less pressure FORCE

18. 14. What type of barometer is shown above?

19. 14. What type of barometer is shown above? Mercury barometer.

20. 15. How did the air pressure change from 1:00 AM to 2:00 PM? The air pressure decreased from 1:00 AM to 2:00 PM. The level in the barometer is lower and the reservoir is higher.

21. 15. How did the air pressure change from 1:00 AM to 2:00 PM? The air pressure decreased from 1:00 AM to 2:00 PM. The level in the barometer is lower and the reservoir is higher.

22. 16. What happened to the level in the reservoir from 1:00 AM to 2:00 PM? The level in the barometer is lower and the reservoir is higher.

23. 16. What happened to the level in the reservoir from 1:00 AM to 2:00 PM? The level in the reservoir increases from 1am to 2pm.

24. 17. Write down two things that you know about this diagram: Pay attention to the temperatures in the atmosphere. When you get to the next layer of the atmosphere, what happens to the direction of the temperature?

25. Current Air Pressure in San Diego http://weather.noaa.gov/weather/current/KNKX.html