1. At 15
15. 3ppt
Air Pressure
CH 15 Prentice Hall p

2. Air Lab Problem: Hypothesis: Materials: Does Air Have Mass?
Air has mass.
Air doesn't have mass.
Materials:
Stopwatch Graduated cylinder balance beaker metric ruler

3. Air Lab Procedure: Data/Obs: (Record Obs) Conclusion:
Write a Step by Step Procedure
Start with a verb.
Data/Obs: (Record Obs)
Conclusion:
Identify the Problem, Hypothesis, explain if data supported it or not.

4. Balloon In Jar
Problem: What are ways the balloon can be inflated in the jar?
Hypothesis:
Blowing in tube B will inflate the balloon.
Pulling air out of tube A will inflate the balloon. A B

5. Balloon In Jar (Observations)

6. Demonstrations
Empty Water Bottle
Peeps
Shaving Cream

7. Empty Water Bottle Problem: Hypothesis: Observations:
What will happen to the water bottle in the vacuum?
Hypothesis:
Observations:
The water bottle expanded.

9. Peep Show Problem: What will happen to the peeps in the vacuum?
Hypothesis:
Observations:
The peeps grew larger.

10. Shaving Cream Problem: Hypothesis: Observations:
What will happen to the shaving cream in the vacuum?
Hypothesis:
Observations:
The shaving cream grew and expanded upward.

11. M D = V mass volume density pressure Properties of Air
Air has the following Properties:
mass M D =
volume V
density
pressure

12. Air Molecule Model Gases consist of molecules which have:
mass and occupy a volume.
Therefore: they have density.
These molecules move randomly and bump into each other.

13. D M = V M D V Density The amount of mass in a given volume of air.
Density=mass/volume M D V x M D V =

14. Air Molecule Model D M = V 1g = M = ? 13g M = ? V 10cm3 = V 10cm3 =
Calculate the density in each box. 1g = M = ?
13g M = ? V
10cm3 = V
10cm3 =
13g
13g D =
D=1.3 g/cm3
D=1.3 g/cm3
10cm3
10cm3

15. Air Molecule Model Situation 1V =
Calculate the density for each side.
Draw a line to show where the wall should move? 1g = M = ?
13g
26g M = ? V
10cm3 = V
10cm3 =
26g
13g D =
D=2.6 g/cm3
D=1.3 g/cm3
10cm3
10cm3

16. Air Molecule Model Situation 1
D=2.6 g/cm3
D=1.3 g/cm3
The density is greater on the left, therefore pressure is higher.
There are more molecules on the left side and there will be more molecules striking the wall.
As a result, the wall will move to the right.

17. Air Molecule Model Situation 2
Calculate the density for each side. Draw a line to show where the wall will move? 1g = M = ?
13g M = ? V
20cm3 = V
10cm3 =
13g
13g D =
D=0.65 g/cm3
D=1.3 g/cm3
20cm3
10cm3

18. Air Molecule Model Situation 2
D=0.65 g/cm3
D=1.3 g/cm3
The density of air is higher on the right, therefore the pressure is greater.
The molecules on the right side will hit the wall more frequently,
therefore the wall will move to the left.

19. Pressure The force on an area or surface.
More mass in a given volume = a higher density. As a result pressure will be greater.

20. (Air) Pressure
The result of the weight of a column of air pushing down on an area.
The weight of a column of air above the desk = the weight of a large school bus.

21. Desk Vs Air Pressure Why isn’t the desk crushed?
Molecules of air push in all directions.
The pressure is balanced by the air pushing up on the desk.

22. Balloon In Jar (Explanation)

23. Balloon In Jar

24. Egg Demonstration Problem: Hypothesis: Observations:
What will happen when the egg is placed on the bottle once the paper is lit?
Hypothesis:
The egg will be pushed into or pushed off the bottle.
Observations:
The egg gets pushed into the bottle.

25. 1,2,3 Candle
Problem: How will placing a drinking glass over lit candles sitting in a pie pan filled with water affect the water in the pan?
Hypothesis

26. 1,2,3 Candle Diagram

27. Soda Can Problem: Hypothesis: Observations:
What will happen to the heated can when the opening is sealed with water.
Hypothesis:
The can will….
Observations:
The can is crushed.

28. Speed of Molecules & Temp
What happens to the speed of the molecules when temperature is increased?
What happens to the amount of times the walls are hit?

29. Speed of Molecules & Temp
What happens to the speed of the molecules when temperature is increased?
What happens to the amount of times the walls are hit?

30. Speed of Molecules & Temp
What happens to the speed of the molecules when temperature is increased?
What happens to the amount of times the walls are hit?

31. Speed of Molecules & Temp
What happens to the speed of the molecules when temperature is increased?
What happens to the amount of times the walls are hit?

32. Thermal Energy
Is the total energy of motion in the molecules of a substance.
Gases are made of molecules that are constantly moving. The faster they are moving the more energy they have.
Fast
More Energy
Slow
Less Energy

33. Temperature
The average amount of energy of motion in the molecules of a substance.
It is a measure of how hot or cold something is.
More Energy
Warmer
Less Energy
Cooler

34. Measuring Temperature
Thermometer- An instrument used to measure the temperature, consisting of a thin, glass tube with a bulb on one end that contains a liquid, usually mercury or alcohol.
Liquids expand when heated or contract when cooled.
It is measured in degrees Celsius or Fahrenheit.
Freezing 0°C = 32°F
Boiling 100°C = 212°F

35. Temperature and Volume
What happens to the volume of a gas when it is heated?

36. Temperature and Volume
What happens to the volume of a gas when it is heated?

37. Temperature and Volume
What happens to the volume of a gas when it is heated?

38. Temperature and Volume
What happens to the volume of a gas when it is heated?

39. Air Molecule Model Situation 3
Heating air molecules increases their energy making them move faster.
As a result, they will hit the wall more often, moving the wall to the right.
Lowers the pressure on the warmer side
Increases pressure on the cooler side.
Faster
Molecules
Slower
Molecules

40. Air Molecule Model Situation 4
Cooling air molecules decreases their energy making them move slower.
As a result, they will hit the wall less often, moving the wall back to the left.
Pressure on the right side is higher, pushes back towards the left side which has a lower pressure.
Slower
Molecules
Faster
Molecules

41. 1,2,3 Candle Diagram

42. 1,2,3 Candle Diagram

43. Egg Demonstration
Diagram Explanation:
Written Explanation:

44. Can Demonstration
Diagram Explanation:
Written Explanation:

45. Measuring Air Pressure
A barometer is used to measure air pressure.
Mercury Barometers
Aneroid Barometers

46. Mercury Barometer The first barometers.
Pressure pushes on the surface of the mercury.
When pressure increases the mercury rises up the tube.
When pressure decreases the mercury falls in the tube.

47. Feeling the Pressure Which barometer shows a higher pressure?
Which barometer shows a lower pressure?

48. Aneroid Barometer “without liquid” Uses an air tight metal chamber.
The chamber is sensitive to changes in air pressure.

49. Units of Air Pressure Weather Reports use inches of mercury.
National Weather Service Maps use millibars.
1 inHg = millibars

50. Air Pressure and Density

51. Altitude Affects Pressure
Altitude – elevation
Air pressure is the weight of a column of air pushing down on an area.
Where is the pressure greater/less?

52. Altitude Affects Pressure
Less weight at the top- so there is lower air pressure.
Sea-level has the weight of the whole atmosphere on it.- Pressure is greatest here.

53. Altitude Affects Density
As you increase in altitude, the density of air decreases.
Air pressure decreases as altitude increases.
As air pressure decreases so does density.

54. Altitude Affects Density
As you go up, there are fewer molecules.
However: The percent of a gas in the atmosphere always stays the same at any altitude.
78% Nitrogen
21% Oxygen

55. Isobar Maps

56. Rules for Drawing Isobars
Lines connect areas of __________pressure. H L
Cloudy
(Lousy)
Weather
Sunny
(Happy)
Weather
Set an interval that is appropriate for the change in pressure.
Make sure all points on one side of a line are higher and lower on the other.

57. Practice Drawing Isobars
. 1008
. 1006
. 1005
. 1004
. 1003
. 1007
. 998
. 1002
. 1001

58. Practice Drawing Isobars
Draw Isobars on the diagram below. Mark the center of low pressure and high pressure with an H and L.
Interval = ___________________
.998
.996
.1000
.1012
.1013
.1007
.1009
.1015
.1004
.1010
.1020
.1005

59. Drawing Isobars

60. L H Isobar Maps on RHW Isobars connect lines of equal pressure. Cloudy
(Lousy)
Weather H
Sunny
(Happy)
Weather