Here we construct an aneroid (without
fluid) barometer from a
collection of simple materials that you can find at the supermarket and
local hardware store. Your barometer can be used to track changes in
with weather or it can be used as an altimeter. It is also affected by
temperature, so it will provide good practice in the experimental
technique of "holding independent variables constant".
While we've posted this exercise on the L. M. Nixon Noon Science
website, the calibration and analysis is probably at the extreme limits
of the skill level of
the typical 5th grader, even for our recently-simplified version.
But let me know if I'm wrong!
1. Large balloon, 11" or
larger. Get a good quality balloon; the cheap ones slowly leak.
2. Rigid plastic or glass cup. If you select plastic, spend a
little extra and get very heavy-grade cups.
3. Rubber bands (#30 size seems good, they are about 2" long.
They'll need to fit tightly around whatever cup you select.).
4. Hardwood dowel (1/8" diameter x 12" long).
5. Hot glue gun and glue.
6. 8-1/2" x 11" sheet of heavy card stock, such as 90lb Bristol board.
7. Paper ruler, divided into millimeters (pick one from here,
8. 3" x 1/2" x 16" piece of lumber for a base.
9. Sharp scissors.
10. A piece of #100 grit sandpaper or an emery board for filing a point
onto the dowel.
Prepare the Aneroid Chamber
1. Blow up the balloon to stretch it out, and then release the air. Cut
off the neck of the balloon so that you can reach into the balloon with
your fingers and stretch the balloon out and over the top of the
Make sure that the inside
surface of the ballon ends up on the outside
so that humidity trapped in the inside of the balloon will not be
trapped in the chamber. You may have to practice this several times to
do it without ripping
the balloon, yet at the same time obtaining a good seal over the top
of the cup.
Note: Some like to stretch out the balloon by simply pulling it in
hands. My personal bias is that this does not stretch the balloon
uniformly. But blowing up heavy balloons is sometimes difficult for
2. Wrap several rubber bands around the top of the cup and over the
balloon to help insure a tight air seal.
Add The Pointer
The long dowel will be glued to the balloon surface so that it extends
from the center of the balloon outwards over the edge of the cup.
Use two dabs of glue; one at the center of the balloon and one at the
rim of the cup.
Assemble The Stand and
Load your computer printer with some heavy paper (80 lb Bristol board,
8-1/2" x 11") and print this
on the paper. Cut it out and
fold it up to make the stand. Glue (or double-stick tape) the
"tabs" to the "base".
Cut out and attach this
ruler scale to the middle of the stand. Put "zero"
toward the base of the stand.
Attach All Parts to the
1. Position the cup and scale/stand (without glue) onto the wood
base. See the picture below.
2. Use hot glue to attach just the bottom edge of the cup to one
the base by applying two or three blobs of glue, evenly spaced, around
the outside edge of the cup. Position the cup so that the end of
the pointer is near the front edge of the base.
3. Use a small sanding board to sharpen the
end of the pointer so that its position can be determined
precisely. Then attach the scale/stand to the base so that the
touching the scale and is free to move up and down. .
Your First Experiment
1. I'll bet that you've assembled your barometer in your
classroom or your work area at home, and that the room temperature is
about 70F. When your assembly is complete, wait about 10 minutes
for the cup of your barometer to come to room
temperature. Then note the position of the pointer on the
2. Wrap your hands around the cup snugly, but gently (don't
distort the cup with the force from your hands). Wait several
minutes, and record the position of the
If you are a human and not a lizard, your
body temperature is about 98.6F, while the temperature of
your indoor, air-conditioned surroundings is about 70F. By
wrapping your hands
around the cup (the aneroid chamber) you've heated the air in the cup
to nearly your body temperature.
Look at the position of your
barometer pointer. What do you think happened to the pressure in
(chamber)? This picture shows the difference in the pointer
position when my barometer is at room temperature and body
temperature. Which side shows what happens when my hands are on
the cup? Look at the results from your own experiment to find
Using the Barometer to
Measure Altitude - an Introduction.
you live near some hills that are high enough to show a large change in
atmospheric pressure between the bottom and the top (if you're in
Kansas, you're out of luck, in more ways than one). A hill of
1000 feet elevation is certainly enough to show a large motion of the
your barometer. The elevator in a ten story building will show
enough change on your barometer to be visible. Next time you go
to San Francisco, take the elevator up the Transamerica Tower and watch
the change on your barometer! Take a picture of yourself with
your barometer at the ground floor and at the top floor. Make
sure your photo shows the pointer on your barometer.
In our neighborhood close to L. M. Nixon Elementary near Palo Alto, CA,
are lucky to be close to "mountains" of about 2000 feet in
altitude. Our students can use a topographic, or "topo" map, and
ask an adult to
drive them up Page Mill Road from near sea level at the bottom near
Nixon Elementary, up to the top at Skyline Boulevard. By stopping
at identifiable landmarks at intervals of 500 feet or less, you can
of the pointer at each spot. But as you do this, think about the
effect of temperature on the position of the pointer of your
barometer. What can you do to keep the temperature of your
barometer constant? Your car may have "climate control" that can
help. But you might also try to use your hands as a
temperature control. Remember, unless you are feeling sick, your
body temperature is quite constant!
If you are an L. M. Nixon Elementary student, we've posted all of the
relevant topo maps for our drive from Hwy. 280 all the way
up to Skyline Blvd here. Here is a
"topo" map for Nixon school; can you use it to find the elevation
at school? (about 140 feet
mean sea level).
Atmospheric pressure decreases by about 0.25 inches of mercury for each
250 feet in altitude (or 10 millibars per 100 meters). So a climb
thousand feet in altitude will show a change in pressure of about 2
inches of mercury, which is a greater pressure change than you
might usually expect to see due to changes in the weather. But it
will allow us to "calibrate" our barometer so we will know how much
motion to expect as the weather changes. This is about how far my
barometer moves when I drive from Skyline Boulevard down to sea level.
Using the Barometer to
Monitor the Weather - More Introduction.
We'll need to know the actual pressure at
"Nixon School Level" (nearly sea level). The World Wide Web helps
us to do this. In our location, use this
to find the current atmospheric pressure at San Francisco
(SFO) airport. We'll use this to find the atmospheric pressure at
If you are a Nixon student, you will need some help from a
parent! See if you can convince them to read the instructions
first and help you finish your project.
1. Before you start your day's adventure of collecting barometer
data, you will need to find the atmospheric pressure at sea
level. Here is a part of the page for the SFO website
that I "grabbed" on
the morning of April 21, 2006. The column on the far left is the
time of day and the column on the far right is the atmospheric pressure
in "inches of mercury". What is this number? This is the
height of a column of mercury that can be supported by the pressure of
You will need to put this information into a chart. Get a copy
here, and print it out for your experiment.
Write down the date and time
that you start
your data collection, and put the atmospheric pressure at SFO into your
chart like this:
Now start your journey at Nixon school. You might like to use
our already-prepared map that shows a list
of identifiable landmarks
and the corresponding altitude. Decide what temperature control
technique you intend to use with your barometer (either the
air-conditioned-car-and-home technique or the hold-it-in-your-hands
technique). Record the pointer position of
your barometer at Nixon school, and again as you reach each 250 foot
Here is what the information looks like for my barometer; yours will be
different because many things about your barometer will be different.
Now we're ready to fill in the rest of the numbers in the "Pressure"
column. Atmospheric pressure changes by about 0.25 inches of
mercury for each
250 foot change in altitude. So start with the number for the pressure
at SFO and subtract 0.25. Your answer goes in the "250 ft." space.
Keep going all the way down the "Pressure" column, subtracting 0.25"
for each change of 250 feet.
Your calibration is all finished! If you want, you can even
calculate what your pointer position should be at the San Francisco
Airport, and what the air pressure would be at Nixon school (about 0.14
inches of mercury less than at SFO). See
if you can think about how that might be done with the information you
have on your chart.
Now you can use your barometer to monitor the weather! I added
the actual air pressure values to the scale of my barometer so that I
could monitor the barometric pressure without looking at my
When the weather is turning from clear to stormy, the air pressure
often falls. See if you can predict the change in the weather
just from watching your barometer.
Try to build a science fair project with your barometer!