Tornadoes and the devastation they cause have recently been in the news again. This activity allows you to create a safe tornado. It is best prepared in advance by adults for pupils to investigate during the lesson.

To make a tornado, you need two plastic drink bottles, some water and some strong adhesive. Remove the labels from the bottles (two-litre bottles work best). Take the bottle lids and glue them together. Make a hole, 1cm diameter, through the centre of the lids. (This is the hardest part and should be carried out carefully.) If it is impossible to make the hole, an alternative is to use a rubber washer.

One of the bottles should be filled with water to about 10 cm from the top. The double lid should be attached to this bottle. The empty second bottle should now be attached to the double lid, which should be taped to provide support at the join. If you are using a washer you must attach it between the bottles securely, and tape over the join to ensure that the full bottle does not pull away from the empty one.

Standing over a bath or sink, turn the bottles over to check that your seal is tight. The water will drip slowly into the lower bottle, and, as the pressure increases in the lower bottle, air will be forced up into the upper bottle. The water cannot pour into the lower bottle, because it needs to displace the air, and there is nowhere for the air to go.

Place the bottles vertically on a table and shake them in a circular motion to start the water moving. After a few shakes, the water will form a tornado and will pour into the lower bottle. The displaced air will travel upwards through the centre of the vortex. To see the motion more clearly you should add glitter to the water.

It is possible to buy a ready-made connector for the two bottles. This makes it easier for students to assemble and leads to more predictable results.

Sophie Duncan is a physicist and programme manager with Planet Science (formerly Science Year) www.planet-science.com