Science corner

14th March 2003 at 00:00
Under pressure: Sophie Duncan keeps a weather eye open

Barometers were invented in the mid-17th century to measure the height of hills, as air pressure decreases the higher we climb, but they soon became popular in Britain because of our obsession with the weather. Initially they made use of mercury, but as this made them difficult to transport an aneroid mechanism was soon created.

You can try these simple designs to make your own barometer. The first makes use of liquid, and the second does not.

Attach some narrow plastic tubing along a rules, starting at the 2cm mark.

Place the ruler and tube into a straight-sided glass, and fix the ruler in place. Half fill the glass with water. Carefully suck water into the tube, until the level of water in the tube and the glass are the same. Seal the end of the tube using Blu-tac.

Position your barometer away from heaters and draughts to avoid changing temperature. Take measurements of the water level in the tube regularly.

When the air pressure is high, the water is forced into the tube, and the level rises. When the air pressure drops the level falls.

Another barometer design can be made using an opened can. Cut a piece of balloon to fit over the opening of the can. Fix it in place with an elastic band. Stick a straw horizontally across the surface of the balloon, with the straw tip in the centre.

Place a vertical card with a scale on it opposite the end of the straw. The straw will move up and down as the air pressure changes. When it increases, the balloon will be pushed downwards, and the straw will move upwards.

By encouraging your students to make regular measurements with their barometer and noting the weather conditions, they will soon be able to have their own forecasts.

Sophie Duncan is project manager for science at the BBC www.bbc.co.ukscience

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