Barometer

Description:
The aneroid barometer is an instrument that does not use liquid in measuring the pressure of the air.  The atmospheric pressure changes as the weather changes.  It goes up and down.  We say the pressure is rising, is falling, or is steady.  An aneroid barometer works with a small capsule that acts like a bellows.  Air has been removed from the capsule.  When the air pressure increases, the sides of the capsule are pushed in and the connected needle rises (clockwise).  If the air pressure decreases or falls, the sides of the small capsule puff out and the needle moves in the counter clockwise direction.  The numbers are based on the principle that atmospheric pressure supports 30 inches of mercury in a tube of mercury with one end sealed.

Goal:
Students will understand that the changes in weather occur with changes in air pressure and that a barometer is used to reflect the changes.

Instructions for Set Up
At sea level to 300 feet above, the barometer is factory set.  If the instrument needs to be set, call the local airport for the local reading.  With a screwdriver inserted into the slot on the back, gently turn the indicating hand to the desired reading.
When you first receive the barometer, gently tap the glass to make sure the hands are free.  Then set the marking hand over the indicating hand.  A rising hand over a period of hours indicates fair weather.  A falling hand indicates a low pressure system on the way and poor weather.  When the barometer is steady, it reflects an ongoing pressure system:  no changes.  A change of a degree either way in a few hours indicates quickly changing weather.  A slow change of .3 or so a day indicates weather coming in 12 to 24 hours.  A quick rise in the barometer reading often indicates high winds and unsettled weather.

Barometer
Activity:  Water and Air

Objective:  Students will be able to describe one effect of how powerful air pressure is in our world.

Materials:
a glass of water
a piece of strong cardboard larger than rim of glass

Time:  30 minutes

Background Information:
This is a well-known experiment that dramatically illustrates how air pressure is all around us.  It is a great way to start a discussion of air pressure.

Procedure:
Do not tell the students that you are demonstrating air pressure.  Let them predict how this experiment works.  Make sure you have tried it and are comfortable with it before beginning.
    Fill a small glass of water to the brim.  Place a thick piece of cardboard over the top.  The cardboard must be thick enough so  that it will not saturate during the experiment.  Keeping your hand on the cardboard, quickly turn the glass and cardboard upside down.  Take your hand away without breaking the seal.  Air pressure against the cardboard will support it.
    Ask the students how they think the experiment worked.  Discuss the power of air pressure.  We do not feel air pressure because the air in our body pushes out.  But it is a prime factor in our weather and our lives.
    *Experiment adapted from Taylor, Barbara. (1993).  Weather and Climate.  New York:  Kingfisher Books.

Barometer
Activity 2:  Measuring the Pressure of the Air

Objective:  Students will be able to read a barometer and interpret the readings.

Materials:  Aneroid Barometer

Time:
45 minutes day 1
15 minutes each subsequent day for three days
30 minutes last day (day 5)

Background Information:
The air that surrounds the earth creates atmospheric pressure.  As you go higher into mountains or in a plane, the air is thinner and the pressure is less.  At sea level on a normal day, this pressure supports about thirty (29.92) inches of mercury in a glass tube that is sealed at an end.  A man named Torricelli, an Italian scientist, discovered this in the 1600ís.  A man named Pascal discovered that changes in air pressure related to changes in weather.  Within a few years of Torricelliís findings, Pascal had created the first barometer.  They became extremely popular in Europe.  They were used by sailors to predict weather.
    Changes in air pressure are caused by the difference in air temperature above the earth.  Land masses and areas of water change the temperature of the air above them.  These changes create wind and cause pressure patterns to develop.  The wind moves these pressure patterns that change as they pass over mountains, oceans, and other areas.
    When the air is dry, cool, and pleasant, the mercury or barometer reading rises. When the air is warm and wet, the barometer reading falls. When the air pressure falls, it usually indicates some type of storm or wet weather is coming.  When it rises, it often means clear weather.  If the barometer remains steady, there will be no immediate change in the weather.  The more rapid the change, the sooner the weather will change.  A change of even one-tenth of an inch is a significant change.

Procedure:
Discuss air pressure as introduced above.  Have students predict what the current barometric reading might be (high or low) based on the weather outside.  Introduce the aneroid barometer.  (Note:  it is not as accurate as a mercury barometer, which is still used by most professional weather stations.)  Show the students how to set the marking hand.  Find a place to keep the barometer so that the students or a selected student might read it two times each day, placing the marking hand over the indicating hand each time. Have the students begin their journals with this first reading.  At the end of each day the student who has taken the readings shares them with the other students, noting the weather and predicting the upcoming weather.  At the end of the week, discuss what the students have observed and learned.
 Anemometer  Rain Gauge  Hygrometer  Probe Thermometer


This curiculum project was funded by the Colby Partnership for Science Education, the Howard Hughes Medical Institute, and the Bell AtlanticFoundation.