Agenda for today, 7-Mar.-12

Today’s Focus: Air PressureCA 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?

1. REVIEW What is density? (see page 142)

1. REVIEW What is density? (see page 142)

Density is a measure of how much mass there is in a volume of a substance.

2. “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.

3. What do you think the air around us is made up of (what is air)?

4. Hypothesize how we can test that air has mass. (262) Use the balance (scale) to find the mass of a deflated balloon…Find the mass of the inflated balloon. Compare ….

5. Why does air have mass? 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. (263)

6. How can you calculate the density of a substance? (263)

6. How can you calculate the density of a substance?

Mass=

VolumeDensity

Getting crushed!

Getting stepped on!

Is this bursting your balloon?7. What is pressure?

Why were these guys not worried?

Pressure the force pushing on an area or surface

Can anyone name some familiar forces acting on you right now that create pressure?!

FORCE

AREA

PRESSUREFORCE

AREA=

• gravity (your weight)• weight of the air (air pressure)

7. What is pressure?

What force causes air pressure? GRAVITY!Air Pressure- The weight of a column of air pushing down on an area

hundreds kilometers

Area = 1 m2

column of air How much does this column of air weigh?

11.5 tons!

Why aren’t we crushed?

Air inside you is at the same pressure!

Force(weight)

PRESSUREFORCE

AREA=

8. What is atmospheric or air pressure?

Let’s return to the bed of nails… here’s whythose guys didn’t need to worry!

FORCE

AREA

FORCE

AREA

PRESSUREFORCE

AREA= PRESSURE

FORCE

AREA=

BOOM!

Because the force is divided into a larger area on thebed of nails, the pressure on the balloon is smaller than with the single nail.

bed of nails single nail

9. What is a barometer?A barometer is an instrumentthat 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 in inches or millimeters of mercury

height =pressure

10. Use page 264-265 to compare two similarities and two differences between a

mercury barometer and an aneroid barometer.

Mercury Barometer

Aneroid Barometer

11. 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.

12. In which layer of the atmosphere does the air pressure change the most?

The troposphere

13. What is the air pressure when the elevation is zero? (standard air pressure)

1013.2 mb

14. Why does air pressure change with elevation? (265-266)

At higher elevations, there are fewer air molecules to cause the air pressure. The air has less weight pressing on it.

As elevation increases, the number of molecules of air in a certain volume decreases

elev

atio

n

At higher elevation, less air above you,less weight (force), less pressure

FORCE

FORCE

15. What type of barometer is shown above?

15. What type of barometer is shown above? Mercury barometer.

16. 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.

16. 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.

17. 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.

18. If there is more pressure pushing on the reservoir, what happens to the level in the tube? The level in the tube goes up.

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

18. If there is more pressure pushing on the reservoir, what happens to the level in the tube? The level in the tube goes up.

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

18. If there is more pressure pushing on the reservoir, what happens to the level in the tube? The level in the tube goes up.

19. Write down two things that you know about this diagram

Varying temperatures inthe atmosphere.

When you get to the next layer of the atmosphere,what happens to thedirection of the temperature?

Current Air Pressure in San Diego

http://weather.noaa.gov/weather/current/KNKX.html