# How to make a barometer

You may ask how to make a barometer quickly and easily.  Or how to demonstrate the principles involved to your class if you teach science.

This fun-to-build device should work well once completed, and making a barometer will help demonstrate the principles outlined in the second half of this article.

To make your own barometer, find a jar, some water, a metric ruler, a drinking straw, some good tape that will work even when wet, and chewing gum (pick a flavor you like). Then come back here.

First of all, tape the ruler to the inside of the jar so that you can read the numbers and it stays standing upright.

Second, tape your straw to the ruler, but don't cover the numbers. Leave a small space between the end of the straw and the bottom of the jar.

Third, chew your gum for a while.

Fourth, put some water in the jar - half-filled should do.

Fifth, suck up a little water into the straw, but not all the way to your mouth. Halfway up will be fine.  Then plug the top end of the straw with your gum. Make a good seal. This may take a little practice.

Sixth, make a tick mark to remember where the water level is in the straw. Use a permanent marker.

Seventh, wait and watch. The water level will change up and down. When it moves up, it means higher atmospheric pressure.

Eighth is really How to make a barometer work, calibrate:  compare the movements in millimetres with the changes in reported barometric pressure.

You can get actual pressure readings from your local weather reports or another barometer if you have one.  Determine how many observed pressure units, either kiloPascals or hundredths of an inch of mercury each millimeter on the ruler represents.

For best results, use your barometer indoors where the temperature remains nearly constant.  Changes in the water temperature can have some undesired effect on your pressure readings, and the fewer variables affecting the readings given by a precision instrument, the better your experiment will work.  If you're really curious, here are a few other barometer designs for the kids to try.

Make a barometer - using an air balloon.

How to make a barometer - with a can and a pin.

Projects like this encourage kids to think and interact with their world.  The activity feeds their fascination, gives them reasons to ask questions and explore and discover themselves as well as their surroundings.

Some of many people's favourite childhood memories revolve around classroom projects like this, whether they are socially-interactive and independently undertaken.  Let them love their learning years.

## How to make a barometer work?

The air pressure on the surface of the water in the jar in our simple example causes it to push upward on the water in the straw.

That's why increasing the ambient pressure causes the column to go up.

The mass of air above the water inside the straw does not change, but the increased pressure causes it to occupy a smaller space, provided the temperature does not change. The whole system seems to know how to make a barometer respond appropriately.

One of Galileo's students, Evangelista Torricelli, wrote We live submerged at the bottom of an ocean of elementary air, which is known by incontestable experiments to have weight. This has become a famous quotation in the science of meteorology.

Barometers have been developed to help us determine how much weight that is. Traditional barometers come in two types:

Liquid barometers - someone figured out how to make a barometer with a vertical tube containing either water or mercury. If it has mercury, which is far more common, its height changes from around two to nearly three feet at ground level as the atmospheric pressure changes.

How often does that happen? Every day, but not by a lot, usually. When people, usually American citizens and pilots, say that the pressure is 29 inches or some number close to that, they are talking about mercury.

Most often, this is the height the mercury column would be if it were "corrected to sea level". Mathematically adjusted to give the correct pressure if the elevation were equal to zero.

What does elevation have to do with it? The air pressure drops off quickly as you climb uphill and this effect cannot be ignored when interpreting pressure data.

Aneroid barometers - a sealed container cannot let air escape. When you have a  sealed container with flexible walls, the walls move inwards and outwards as the air pressure outside to chamber changes. And we can measure how much they move.

How to make a barometer improve aviation safety? Airplanes have an aneroid barometer on board to help pilots figure out how high they are above the ground. They call this device an altimeter. See more about this on the Weather Equipment web page.

Have fun with your barometer experiments.

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Make your own barometer for measuring air pressure.

How to construct a barometer using everyday items.

A few minutes spent making a barometer can be time well spent.