Air PressureAir PressureCH 15 Prentice Hall

p.509-514CH 15 Prentice Hall

p.509-514

At15

15. 3ppt

• Problem:– Does Air Have Mass?

• Hypothesis:– Air has mass.– Air doesn't have mass.

• Materials:– Stopwatch Graduated cylinder balance

beaker metric ruler

Air Lab

Air Lab

• Procedure: – 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.

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.

Balloon In Jar (Observations)

Demonstrations

Empty Water Bottle

Shaving Cream

Peeps

Empty Water Bottle

• Problem: – What will happen to the water

bottle in the vacuum?

• Hypothesis:

• Observations: – The water bottle expanded.

Peep Show

• Problem: What will happen to the peeps in the vacuum?

• Hypothesis:

• Observations: – The peeps grew larger.

Shaving Cream

• Problem: – What will happen to the shaving cream in

the vacuum?

• Hypothesis:

• Observations: – The shaving cream grew and expanded

upward.

• Air has the following Properties:

Properties of Air

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.

• The amount of mass in a given volume of air.

• Density=mass/volume

Density

Air Molecule ModelCalculate the density in each box.

Calculate the density for each side.Draw a line to show where the wall should move?

Air Molecule Model Situation 1

Air Molecule Model Situation 1

• 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.

Calculate the density for each side.Draw a line to show where the wall will move?

Air Molecule Model Situation 2

• 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.

Air Molecule Model Situation 2

• The force on an area or surface.• More mass in a given volume = a higher

density. As a result pressure will be greater.

Pressure

• The result of the weight of a column of air pushing down on an area.

(Air) Pressure• The weight of a column of air above the desk = the weight of a large school bus.

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.

Balloon In Jar (Explanation)

Balloon In Jar

• Problem:– 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.

Egg Demonstration

• 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

1,2,3 Candle

1,2,3 Candle Diagram

• Problem:– What will happen to the heated

can when the opening is sealed with water.

• Hypothesis:– The can will….

• Observations:– The can is crushed.

Soda Can

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?

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?

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?

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?

• 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 EnergySlow

Less Energy

Thermal Energy

• The average amount of energy of motion in the molecules of a substance.

• It is a measure of how hot or cold something is.

Temperature

More EnergyWarmer

Less EnergyCooler

• 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

Measuring Temperature

Temperature and Volume

• What happens to the volume of a gas when it is heated?

Temperature and Volume

• What happens to the volume of a gas when it is heated?

Temperature and Volume

• What happens to the volume of a gas when it is heated?

Temperature and Volume

• What happens to the volume of a gas when it is heated?

• 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.

Air Molecule Model Situation 3

FasterMolecules

SlowerMolecules

• 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.

Air Molecule Model Situation 4

FasterMolecules

SlowerMolecules

1,2,3 Candle Diagram

1,2,3 Candle Diagram

• Diagram Explanation:

• Written Explanation:

Egg Demonstration

• Diagram Explanation:

• Written Explanation:

Can Demonstration

• A barometer is used to measure air pressure.– Mercury Barometers– Aneroid Barometers

Measuring Air Pressure

• 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.

Mercury Barometer

• Which barometer shows a higher pressure?

• Which barometer shows a lower pressure?

Feeling the Pressure

• “without liquid”

• Uses an air tight metal chamber.

• The chamber is sensitive to changes in air pressure.

Aneroid Barometer

• Weather Reports use inches of mercury.

• National Weather Service Maps use millibars.

• 1 inHg = 33.87 millibars

Units of Air Pressure

Air Pressure and Density

• Altitude – elevation• Air pressure is the

weight of a column of air pushing down on an area.

• Where is the pressure greater/less?

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.

Altitude Affects Pressure

• As you increase in altitude, the density of air decreases.

• Air pressure decreases as altitude increases.

• As air pressure decreases so does density.

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

Altitude Affects Density

Isobar Maps

• Lines connect areas of __________pressure.

Rules for Drawing Isobars

• 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.

Sunny(Happy)Weather

Cloudy(Lousy)

Weather

Practice Drawing Isobars

. 1008

. 1006

. 1005

. 1008

. 1008

. 1006

. 1004 . 1003

. 1007

. 998

. 1004

. 1002

. 1001

. 1007

. 1005

. 1002

. 1002

. 1003

. 1007

. 1004

. 1005

.998

.996

.1000

.1012

.1013

.1007

.1000.1000

.1009

.1015

.1004

.1010

.1020

.1005

Practice Drawing Isobars

Draw Isobars on the diagram below. Mark the center of low pressure and high pressure with an H and L.

Interval = ___________________

Drawing Isobars

• Isobars connect lines of equal pressure.

Isobar Maps on RHW

Sunny(Happy)Weather

Cloudy(Lousy)

Weather