Developed by Susan Frack and Scott Prickett
Air pressure is a measure of the weight of the air. It is always changing. When air is cold and dry it weighs the most. The barometer shows high or rising air pressure. That tells the meteorologist that fair weather is on its way. Air that is warm and damp weighs less than dry air. Then the barometer shows low or falling air pressure. A drop in air pressure usually signals foul weather ahead. Meteorologists use instruments especially made to measure barometric pressure. They are called barometers. They are important tools for forecasting the weather.
- 4 paper grocery bags or shoe boxes
- Styrofoam packing peanuts
- wooden blocks
- sand or gravel
- multi-colored stick-on dots
- white paper
- aneroid barometer
- 1 soup can per student
- non bending straws
- rubber bands
- silicon glue/adhesive
- Describe the different arrangement of air molecules in high and low air pressure masses.
- Compare the temperature of high and low pressure masses.
- Tell how a barometer works.
- Practice using a barometer for 2 weeks.
Video tape a local weather report and show it to the class. Talk about how the weather person figured out what the weather was going to be like: radar, clouds, air pressure, etc. Tell the students they are going to learn about barometers and how they work and how they can be used to predict weather.
1). Fill the grocery sacks/shoe boxes as follows:
- several inches of Styrofoam packing material
- several inches of sand/gravel
- 8-10 partially blown up balloons
- 8-10 wooden blocks-stacked neatly
Seal/staple the tops shut. Try to make A and B appear to be the same and C and D appear to be the same. Label them with the correct letter and set them on a table/floor in front of the children. Ask the students to figure out how they are different without picking up or touching the bags. After several suggestions, let the children pick up the bags and discover that 2 are heavy and 2 are light. Talk about what could make the bags heavy and light. Now open the bags and look at the contents. Try to discover why the heavy things are heavier than the light ones. Size of the object should not be a factor because the bigger objects are actually lighter than the heavier ones--the balloons and the peanuts are larger in size but lighter in weight than the sand and the blocks. Students should see that the light weight objects have larger spaces between themselves and that the heavy items have smaller spaces between themselves. The lighter items don’t fit as well together as the heavy items.
2). Relate these findings to air masses. Heavy air masses have pieces that are close together and there are more pieces in the mass. Light air masses have pieces that are farther apart and fewer in number. Have the students practice this information by pretending to be air masses. A heavy air mass would have many children, close together while a light air mass would have fewer children spread further apart.
3). Put the children into a enclosed circle on the floor and tell them they are a heavy mass of air. Now the sun comes out and warms them up. They start to feel______ (hot, sticky). Do they want to stick close to each other? (NO!) They should start to move apart. They should spread out all around the room. Now they are no longer a heavy air mass, they are a ___ (light) air mass because they are all spread out and have lots of space between them. Now the sun goes away and they begin to get ____ (cooler). Do they want to stay spread out and freeze? (NO!) They want to move close together to warm each other up. They should move back to the circle. Now they are no longer a light mass but a _____ (heavy) mass. After this exercise, the students should figure out that heavy air masses have cooler temperatures and that light air masses have warmer temperatures and that lots of sun can change a heavy mass into a light mass and vice versa.
4). Activity--Appendix A
- Ask the students to remember the grocery bags from the beginning of the talk. The sacks were hard to tell apart without picking them up to feel the difference. Scientists have the same trouble with air pressure. They can’t tell whether the air is heavy or light without measuring it in some way. They measure the air pressure with a barometer.
- Show the students your classroom barometer and talk about how it works--see the directions with the barometer or Appendix B. OR build the “Weather Frog” (see Appendix C.) and use it. It works on the same principle as a barometer.
- Keep track of the air pressure for 2 weeks.
- Compare the weather that occurs 12-24 hours after the barometer readings are done. You should see a pattern of lower barometer readings equaling stormy or wet weather and higher barometer readings equaling sunny, nicer weather. If the barometer doesn’t change, the weather shouldn’t change much either. Therefore, the barometer can really tell you what the weather is going to do the next day.
Each student can make their own barometer to take home to show to parents and describe how it works. They should bring back a signed form from home that says the student described the barometer and how it works to the people at home.
Students will make a model to show the differences between air particles in high and low air pressure masses.
- multi-colored stick on dots
- white paper
WHAT TO DO:
- Give each student one paper labeled, “High pressure/Heavy air” and 1 paper labeled.”Low Pressure/Light Air” and a variety of stick on dots.
- Review: the Heavy air has many pieces, close together; and the Light air has fewer pieces, farther apart.
- Have students complete their models by sticking dots on their pieces of paper.
HOW A BAROMETER WORKS
A barometer has a piece of special metal in it called corrugated metal that squeezes down when heavier air pushes on it and expands up when lighter air does not push so much on it. There is a needle attached to the metal that points to a number on the dial to tell the air pressure. There are also words on the barometer to tell what the weather conditions will do according to the air pressure: rain, change, and fair. Lower numbers indicate low pressure and higher numbers indicate high pressure. Air pressures usually range from 29.00 to 31.00 inches in Nebraska. The number tells how many pounds of pressure the air is pushing down with on every square inch at that time. For example, a barometer reading of 29.5 means that the air is pushing down with 29.5 pounds of force on every square inch of stuff it touches. You don’t seem to feel this pressure because it is spread evenly over everything. Think about someone stepping on your foot with a tennis shoe. The flat sole of the shoe evenly distributes the weight of the person over your whole foot and it doesn’t hurt too much. But if that same person had on a spike heeled shoe and just stepped on your instep with that heel, it could leave a bad bruise. The person’s weight is concentrated all in that tiny, spiky heel!! OUOOOOCH! So, think of air pressure as a tennis shoe and not a spiky heel!
This little frog will “hop” up and down the ladder to tell the weather just like tree frogs in the jungle!! It works on the same principle a barometer does.
- 2 1/2 inch long strip of thin copper metal, 1/2 inch wide
- 2 inch sewing needle
- cardboard disc, 1 1/4 inch diameter
- 1/4 inch glass bead
- fine wire that will support the weight of the paper frog
- cardboard ladder
- 4 inch tall glass jar with straight sides (no slants)
- mylar foil circle, large enough to cover the top of the jar and overlap to be secured with a rubber band and glue
- silicon glue
WHAT TO DO:
- Bore holes in the copper strip and bend it into a u-shape.
- Make the frog from green paper and the ladder from cardboard.
- Insert the needle into the holes of the copper strip. It should turn freely. Put tiny dots of silicon glue on the ends of the needle so it can’t slip out of the holes.
- Attach the frog to one end of the fine wire and wrap the other end around the needle several times.
- Glue the copper strip to the middle of the side of the jar. Glue the ladder to the bottom and the top side of the jar so it looks like the frog is sitting on the ladder.
- Attach the bead to one end of the thread and wind the thread around the needle several times. Push the thread through the center of the mylar circle and the cardboard circle.
- Secure the mylar to the top of the jar with glue and rubber bands to make an air tight seal. Pull the thread tight to make the frog sit closest to what the weather is for the day. Knot the thread and seal the thread hole in the mylar and cardboard with a tiny amount of glue.
- When the air pressure is greater, it will push down on the cardboard/foil and the frog will “climb up” the ladder. When the air pressure is less, it will release the foil and the frog will “climb down” the ladder.
BUILD YOUR OWN BAROMETER
- non bending straw
- large balloon
- soup can, label removed
- rubber bands
- cardboard strip
- silicon glue
WHAT TO DO:
- Cut a circle from the balloon that is large enough to stretch over the top of the soup can.
- Stretch the balloon over the can and secure it with rubber bands.
- Glue one end of the straw to the center of the top of the balloon.
- Set the jar next to the wall where the temperature doesn’t change a lot. Hang the cardboard on the wall so the straw almost touches the center of the cardboard.
- Draw a line with the marker where the straw is. Make a mark about 1 inch above the straw and label it, HIGH. Make a mark about 1 inch below the straw and label it, LOW.
- Watch the straw for the next few days. The balloon will move it up or down as the air pressure changes. When the pressure goes up, the straw will go higher and when the pressure gets lower, the straw will dip lower.
- Higher air pressure indicates fair weather and low air pressure indicates cloudy, wet weather.