# Strip show

It's amazing what you can do with a loop of paper, says Mike Driver

Children are fascinated by magic, having seen magicians such as Paul Zenon or David Blaine on television. Magical scientific effects can be used as a powerful motivator to engage children's interest in science, with the explanation stimulating thinking skills.

Here is a "trick" which is popular with primary teachers and pupils. It is called the Afghan bands, or properly, the Mobius strip, and depends upon the fact that the properties of a loop of paper are altered by putting a twist into the paper, as discovered by the mathematician August Ferdinand Mobius in the 19th century.

What children learn from this trick is that the properties of a material depend not only on the material, but also on its form. In this case whether the loop is normal or twisted. This has wider application of course than just paper loops. The most familiar example to children will be that a sheet of paper is very flexible, but paper folded concertina fashion is much stronger.

Another area of the curriculum, of importance in primary science, is the properties of solids. Children tend to think that solids are hard and cannot be poured like a liquid. But powdered solids or crystals can be poured, and thin fibres of solid, for example cotton, can be very flexible and soft to the touch. Such variation can cause children problems in understanding unless they know that the properties of a solid depend also upon its form. For example, is it a block, a thin sheet, fibres or powder or crystals?

The trick requires preparation. Three large paper loops, about 7.5cm wide are prepared from lengths of newspaper. The first loop is prepared normally. The second loop has a single half-twist put in the paper before the ends are taped together. The third loop has a full twist put in the paper before the ends are taped together. Because the loops are large the twists in some of the loops are not readily seen by the children. Label the loops A, B and C respectively.

The children are asked to predict what will happen when the paper is cut down the centre all the way around the loop. They normally predict two separate loops will be formed, which is correct for a normal loop.

Get three volunteers from the class. Make a starter hole in each of the loops. Then ask the three helpers to cut down the middle of each strip until they have cut all the way around. Make some "magical" hand movements over the children holding strips B and C. Loop A produces two narrower loops when cut. Loop B makes one large loop. Loop C makes two linked loops.

This is a dramatic demonstration which shows that the properties of a solid are altered by its form. In this case, whether it is twisted or normal. It is also an interesting starter activity when looking at the properties of solids, liquids and gases.

Follow-up work could involve children classifying a number of materials as solids, liquids or gases. In addition to the normal examples of blocks of wood, metal and liquids, such as water, and air in a syringe, children could be given more difficult examples of solid materials to classify to consolidate the children's understanding that properties of solids are affected by their form. The materials could include a tea cloth (solid made of thin fibres, soft to the touch), sand (solid consisting of grains, fixed volume, but can be poured ) and a bath sponge ( solid containing bubbles of air, can be squashed).

'MASKS: magical activities for stimulating interest in key stage 2 science', by Mike Driver, pound;17.50. 'SNAKS' (stimulating novel practical activities for key stage 2 science), pound;29.95; 'SNAKS2', pound;29.95. Postage: one book pound;3.50; two pound;7; three pound;8.

Books are photocopiable, with teachers' notes and pupil sheets. Follow-up activities provided. Sample materials and free downloads of worksheets: www.strawberryfieldltd.co.uk; tel: 01833 627227; email: orders@strawberryfieldltd.co.uk

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