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The sense of touch

How sensitive are you? Our skin is covered with millions of receptors that are sensitive to different things - touch, pressure, temperature and pain.

Some parts of our skin are more sensitive to touch than others. Take a paperclip and bend it into a large U shape, so that the two ends are level with each other. Squeeze the paperclip so that the U is very narrow, and the two ends are close together. Blindfold a student and gently touch the ends of the paperclip on the back of their hand, making sure that the two ends touch the hand simultaneously. Ask the blindfolded student to say if they can feel one or two points. They will probably say they can only feel one.

Move the two ends slightly farther apart and try again. Repeat the experiment until the student can feel both points, and then measure the distance between them. You can repeat this experiment by testing different parts of the body, eg the sole of the foot, fingertip, elbow or forehead.

In each case, measure the distance between the two points of the paperclip as soon as the student can feel both points. Compare the different distances. You can then discuss with your students why the distances vary.

Encourage students to explore identifying objects from their sense of touch. Take a box, and cut out holes on two opposite sides, large enough for a hand to fit through. Take two rubber gloves and cut the hand off one glove, leaving a tube shape, which you attach to the inside of one of the holes. Attach the other glove to the inside of the other hole. Make sure the glove is fixed the right way round so that a student's hand can go through the hole and into the glove.

Place an object inside the box, and put the lid on. Ask students to place a hand into the glove and try to work out what the object is. If they can't work it out, they can put their other hand through the tube on the opposite side of the box. Can they work out what the object is now? Take the lid off the box to find out if they were right.

When wearing the glove, students are less able to get sensory information about the object - without the glove they find it easier to work out what it is.

Sophie Duncan is project manager for science at the BBC

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