Homemade barometers are very easy to make, because, despite the fine appearance of the best quality instruments designed for decoration, barometers are really quite simple devices.
The complexity comes when accuracy, consistency of measurement and clear display of the air pressure measurements are needed.
For a basic barometer, all that is needed something that changes in position with changing air pressure, and a means of seeing the change. And that's very easy to do, using stuff that's easy to find in almost every home.
But before building barometers all over the house or classroom, it's worth remembering that barometers measure Air Pressure, and here's a very simple air pressure experiment that demonstrates that air has weight and that it exerts pressure.
The Air Has Weight Experiment
Take two party balloons and partially inflate them. Tie
them to the ends of a stick or a long ruler and balance
it over some sort of pivot - the back of a wooden chair
will do. While holding the apparatus in place at its pivot
point, put a small hole in the neck of one of the balloons
where the rubber is thickest. It shouldn't burst, but will
start to leak.
As it leaks, the end of the ruler with the inflated
balloon will slowly go down.
What's going on?
Firstly, when you inflate the balloon you are forcing air
into it, at higher pressure than the air surrounding it.
The same thing happens when you breathe in and inflate
your lungs - your chest expands because of the higher
pressure inside. You have also added air to the inside of
the balloon - more air is in the balloon than in the same
amount of space outside it, and the extra weight of air
inside the balloon is the reason for the higher pressure.
When the balloon is punctured, air leaks out, and because
there is less air in the punctured balloon than the
inflated one, the inflated balloon is now heavier, and
weighs its end of the ruler down.
You'll find a neat experiment demonstrating Air Pressure here, involving a tin can. It's a bit
dangerous at home without adult supervision, so here's
The Air Pressure Experiment
You'll need a plastic milk bottle with an air tight lid -
screw on lids are probably best. Partly fill it with hot
water and put on the lid. It now contains water, warm air,
and a little water vapor. Watch what happens as it cools.
The bottle has partly collapsed in on itself. This is
because the warm air has cooled. Normally the air would
take up less volume, but it can't because the bottle is
sealed. So by a fundamental physical law, if the volume
stays the same, which it does, the pressure of the air
must also fall as the temperature drops. This law is
named after Robert Boyle, who also gave the barometer its
name. Nothing more will be said about Boyle's Law, but
it's a very important foundation for engineering and
Back on track then. Because the pressure dropped as the
temperature fell, the pressure inside the bottle is less
than that outside, and the outside air pressure presses
in on the bottle, which, being flexible, starts to bend
and collapse. The process is slightly helped because the
water vapor in the bottle starts to condense from gas
to liquid as the temperature drops, also causing a
If you want to know more about Home Experiments Related to Weather, just follow the link to an
excellent book, and I know from experience it's not just
for kids. And here are some other top introductory weather
And while most scientific attention was concentrated
on the mercury barometer, water based barometers were also
in use, and in big numbers. They were known as the Weather Glass or Storm Glass. Follow the link to find
out more about these elegant weather instruments.
But both of these barometers had their problems, not the
least of which was keeping the mercury or water in its container.
As technology improved, the better, more convenient Aneroid Barometer appeared, and that
is the most common form we see today.
You can also find information on
Setting and Calibrating Your Barometer, elsewhere in this
site, together with reviews of Modern Barometers.
This link will take you back to the Top, or, when you're ready, here's how to return to the Home page. But just before you move on...
You may be interested to know that you can find out more about weather and home weather stations by receiving our newsletter ,"Watching Weather". It's published more or less weekly, and apart from tips on how to use your weather station and understand what it's telling you about the weather around you, it also covers many other weather related topics.
If this sounds interesting, just add your name and email address to the form below. When you join, you'll also receive, totally free, a 20 page guide to setting up and trouble shooting problems in home weather stations.
And I promise that you won't get spammed, and that your sign up details will remain totally confidential.
Sign up now and receive your first issue almost immediately.
ADD TO YOUR SOCIAL BOOKMARKS:BlinkDel.icio.usDigg FurlGoogleSimpySpurlTechnoratiY! MyWeb