Weather

Brenda Lewis                   George M. Pullman Elementary School
                               11311 S. Forrestville Ave.
                               Chicago IL 60628
                               (312) 535-5395

Objectives:

The students in grades k-8 will be able: to define weather, to understand 
pressure, specifically air pressure, to demonstrate the pushing power and
other properties of air, and to be able to understand how a barometer is used 
to measure air pressure. 

Materials Needed:

Teacher-made charts illustrating pressure
High-heeled shoe
Gym shoe
Graph paper
Chalk
Scissors
Masking tape
Teacher made anemometer
Teacher made barometer
Teacher made rain gauge
Balloons
Straws
Glass jars
Erlenmeyer flask
Water
Overhead transparency
Tape
Transparency markers
Chart paper
Poster board

Strategy:

A.  Introduction: Today we are going to learn the answers to the following three
    questions:
1.  What is air pressure?
2.  How do we measure air pressure?
3.  What is weather?  (The working definition of weather is written on the 
    board.)  Weather is the condition of the atmosphere around us.  We see and 
    feel the weather in the wind, rain, sunshine, frost, or fog.  What is 
    atmosphere?  Atmosphere is the blanket of air around the earth.  Wind is 
    defined as moving air. 

Atmospheric pressure pushes downward and affects everything on the earth, 
including your body.  You would be crushed by this force if your body did not 
have its own internal forces which push outward.  One body force that you may be 
familiar with is air in your lungs. 

B.  Experiments and Activities:
To demonstrate that wind is moving air and that air is present, instruct the 
students to wave their hand in front of their face.  The students should 
conclude that wind is moving air. 
Pressure is defined as force per unit of area, and it pushes against the earth's 
surface all the time, but air is constantly moving and changing so the amount of 
pressure it exerts on any one particular place varies.  The weight of the air 
depends to some extent upon its temperature.  Because air is made up of gases, 
it can expand and contract easily.  When air is heated, it expands.  When it 
cools, it contracts.  Warm air is lighter than cold air, so cold air exerts more 
pressure on the earth.  Note: Air is a gas.  How do you measure air pressure? 

Activity

Materials: Graph paper for tracing, Markers, Gym shoe, High-heeled shoe, chalk,
Over-head projector, transparencies, transparency markers 
1. Have the students press their hands down on paper and trace around their 
   hand.  (Graph paper should be used.)
2. The students will count the number of squares that are in the outline of 
   their tracing.  (Partial squares count as one square.)
3. The students are instructed to get into groups of two.
4. The students will trace their partner's shoe, while he stands on one foot.  
   The partner will count the number of squares in the drawing.
5. Now the other partner will stand on tiptoe, while his partner traces that 
   portion of his foot.  The squares are counted.

Special note:  Pressure is expressed in force per unit area.

Activity:  Display a gym shoe and a high-heeled shoe.  Ask, "Which shoe has 
more surface area touching the floor?"   (The teacher writes the following
formula on the chalk board:  Pressure = Weight/surface area = ---lbs. per square 
unit.

Atmospheric Pressure:

Objective: To be able to demonstrate the effects of atmospheric pressure, 
especially its relation to expansion and contraction.

Materials: An Erlenmeyer flask, a balloon, hot plate, and water.

Procedure:  Place a small amount of water in the flask and heat it.  As the 
water begins to boil, place a balloon over the top of the flask.  The balloon 
will inflate.  Remove the flask from the heat and let the water cool.  As the 
water cools, the balloon will be drawn into the flask.  Have the class decide 
why the balloon inflated and then why it collapsed.  The balloon inflated 
because the liquid in the flask changed to a gas and the hot gas pushed out into 
the balloon harder than the outside air pushed on the balloon; the balloon 
collapsed when the steam condensed back to water and the cooler air took up 
less space, generating less pressure inside the balloon, letting the air outside 
push the balloon into the flask.

Activity:  Teacher/Student Made Barometer.
                        
A Barometer is an instrument used to measure changes in air pressure.


How To Make And Use A Barometer

(Make it on a rainy day when the air pressure is low, or it will not work.)

Materials:

1.  Bottle
2.  Bowl
3.  Rubber bands
4.  Thin cardboard
5.  Food Coloring
6.  Metric ruler

Procedure:

1.  Cut a 2.45 cm (1 in.) strip of thin cardboard and draw a scale along both 
    edges.  Attach the cardboard to a bottle using the rubber bands.
2.  Fill the bottle with water so it is three quarters full. Add red food 
    coloring to the water.  Also fill the bowl nearly to the top with water.  
    Turn the bottle over carefully.  Try not to let any water out.
3.  Place your hand over the top of the bottle and turn it upside-down.  Put 
    your hand into the bowl so that the neck of the bottle is under the water.  
    Remove your hand from under the bottle and stand it in the bowl. 
4.  The water level in the bottle will rise and fall with the air pressure, as 
    more or less air pushes down on the water in the bowl.

Note:  Mark the water level on the day you make your barometer.  Find out what 
the air pressure is and write this too.