1. Density and Pressure of Air
Air Pressure 7.2
Density and Pressure of Air

2. The air is made up of molecules.

3. Properties of Air
Eureka Density
Density
Density 2
Air has mass.
Since air has mass, it has other properties, including density and pressure.

4. Density 5 circles per cube Density = Density
Amount of mass in a given volume
5 circles per cube
Density =

5. Density 11 circles per cube Density = Density
Amount of mass in a given volume
11 circles per cube
Density =

6. Temperature Affects Density
6 circles per cube
2 circles per cube
Density =

7. Temperature Affects Density
3 circles per cube
10 circles per cube
Density =

8. Which rises and which sinks?
Density =
Density =
5 circles per balloon
2 circles per balloon

9. Density Eureka Density Density 2
If the molecules are real close the density is higher.
If the molecules are spread further apart the density is lower.

10. Density
Which is Denser?

11. Which cookie has more chocolate chips?B
If I wanted to make a cookie less dense I would use the same amount of chocolate chips just make the cookie bigger.
Cookie A is denser . It has more chocolate chips in the same size cookie than cookie B.

12. Which is state of water is least dense? Most dense?
liquid
Solid
Gas
Molecules move very slowly! They are close together.
Molecules move faster and are more spread apart.
Molecules move very fast! They are very spread apart.
Least Dense
Air and Density Clip
Most Dense

13. Warm Air
Less Dense
Molecules are further apart.
Air is lighter.
Density of warm and cold air.
Cold Air
more Dense
Molecules are closer together.
Air is heavier.

14. Pair/ Share Warm Air Cold Air Less Dense more Dense
Temperature
Warm Air
Less Dense
Molecules are further apart.
Air is lighter.
Temperature
Cold Air
more Dense
Molecules are closer together.
Air is heavier.
Density?
Density?
Molecular spacing?
Molecular spacing?
Weight?
Weight?

15. Cold air sinks because it is more dense and heavier.
Convection currents happen because hot air rises. It rises because it is less dense and lighter.
Cold air sinks because it is more dense and heavier.
Why do convection current occur?

16. Pair/Share
Explain how a convection current works.
Use words like: density, temperature, molecules, weight

17. Air Pressure and Altitude
Less Dense
Most Dense

18. Gravity pulls the air molecules toward the earth, giving them weight
Gravity pulls the air molecules toward the earth, giving them weight. The weight of the air molecules all around us is called the air pressure.
Your weight is the result of gravity pulling your mass down on the bathroom scales. Note that weight has units of a force, such as pounds.

19. Atmospheric pressure is measured by a barometer.
The pressure acting on the surface of the earth is called atmospheric pressure.
It is caused by the weight of a column of air pressing down on the surface of Earth.
Atmospheric pressure is measured by a barometer.
Atmospheric Pressure

20. Air pressure is equal in all directions.
Because air is a fluid, force applied in one direction is distributed equally in all directions. Thus the downward pull of gravity on air molecules produces air pressure in all directions.

21. A Barometer
is used
to measure air pressure.

22. MILLIBARS
The word “aneroid” means “no air,” and refers to the partial vacuum inside the cell. The aneroid cell is shaped like a bellows, so that it can flex as air pressure changes. Increasing air pressure compresses the cell, causing the needle to register a change. Decreasing pressure allows the cell to expand, causing the needle to move in the opposite direction.
The use of inches of mercury is a hold-over from the days of mercury barometers. It refers to the actual height of mercury in the glass tube. Millibars are metric system units, and as such are readily understood by scientists around the world.
An aneroid barometer uses a cell which has had most of the air removed.
As the air pressure around the cell increases, it presses on the cell, which causes the needle to move Barometer Clip

23. Low altitude = high air pressure High altitude = low air pressure
ALTITUDE AND AIR PRESSURE
So why is it harder to breath at higher altitudes?
Altitude vs Air pressure Clip
The lower we travel down into the atmosphere the more weight there is above, and so the tighter the air is squished or compacted.
Low altitude = high air pressure
High altitude = low air pressure

24. Since pressure changes with altitude…
As we have noted earlier, higher elevations have fewer air molecules pressing downward, and so atmospheric pressure is lower. This means a barometer will read lower as it is carried to a higher elevation. Airplanes use a special type of barometer, called an altimeter, to measure altitude.
…how does changing altitude affect a barometer?

25. Barometric pressure goes down.
As elevation goes up
Barometric pressure goes down.
This is an inverse relationship.

26. Can you feel air pressure?
When you take off or land in an aircraft, your ears may hurt or feel uncomfortable. This is because your eardrums can feel changes in air pressure as the aircraft moves quickly up and down.

28. Astronauts wear space suits so the can pressurize themselves in the space suit. With out a space suit an astronaut would explode. More inside body pressure than outside pressure.
Submarines have to be made very strong to withstand the enormous pressure exerted by the water. If they go too low in altitude they will implode.
9 min video on Air pressure

29. Why would this be important?
Most aneroid barometers have a needle which can be set to remember the previous reading.
Why would this be important?
Knowing how the air pressure is changing is as important as knowing the actual barometric reading. The set needle allows students to compare the current reading to the previous one. If the current reading is less than the previous one, the barometric pressure is falling. If the current reading is more than the previous one, the pressure is rising. If it is the same as the previous reading, the pressure is said to be steady. Weather forecasters often use the phrases “falling barometer,” “rising barometer,” or “steady barometer” as a way of referring to the change in atmospheric pressure.

30. Changing Pressure A rising barometer = increasing air pressure.
This usually means:
Rising barometer readings indicate that a high pressure system is approaching. Higher atmospheric pressure is usually associated with fair weather and clearing skies.

31. Where’d the hula dancer go?
Changing Pressure
A falling barometer = decreasing air pressure.
This usually means:
Where’d the hula dancer go?
Falling barometer readings usually indicate the approach of an area of low pressure. Low pressure readings are usually associated with storm systems. Tornadoes and hurricanes can produce very low barometric readings.

32. Why do baseball players like to play in Denver, Colorado?

33. Heat wind and pressure clip