Science corner

9th September 2005 at 01:00
Sophie Duncan makes an Archimedes screw

Invented in the third century BC, the Archimedes screw is a simple mechanical device that enables water to be moved upwards. It has been mainly used in irrigation, but can be found in other places too. These devices are easy to make, giving your students the opportunity to find out how they work.

Take a one-litre plastic bottle and cut off the bottom. Find a thin stick at least 6cm longer than the length of the bottle. Cut a window from the top of the bottle - before it tapers inwards - about 4 cm wide and 4 cm high.

Hold the stick against the bottle and mark the position of the top of this window on the stick. Draw around the bottom of the bottle and use this template to cut out six circles of thin card and number them one to six.

The circles need to fit snugly inside the bottle.

Make a hole in the centre of each piece of card, large enough to push the stick through the centre. Cut from the edge of the circle into the centre on all six pieces of card. With the cut at the top, mark the left side of the cut A, and the right side B. Attach flap B on circle 1 to flap A on circle 2, and then attach flap B on circle 2 to flap A on circle 3. Repeat with each circle until you have a long screw shape.

Hold the circles together and push the stick through them. Attach flap A of circle 1 to the bottom end of the stick, pull the circles so that they are evenly spaced and attach flap B of circle 6 to a line marked towards the top of the stick. Push the stick and screw into the bottle, ensuring that the stick comes out of the mouth. Turn the stick to ensure that the screw works.

Take a bowl full of small lightweight balls (for example Maltesers) and place it on a table. Put an empty bowl on several books. Position the screw with the bottom immersed into the balls and the top window over the second bowl. Turn the screw. The balls should travel up the slope into the upper bowl. Try the experiment with only one ball to follow how it travels.

Consider other materials you could move.

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

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