Break - dancer

From TOYS AND TALES WITH EVERYDAY MATERIALS, Tara Publishers

Head over heels This dancer reels If he's not careful He'll throw up his meals

What it is made of

An empty thread reel A thin and flexible stick, 35 cm 2 pieces of string, 25 cm each Chart paper as needed

How it is made

1. Make two holes through the reel, one below the other, fairly close together. The holes should not be too close to the centre.

2. Pass two pieces of string, one through each of the holes.

3. Bend the stick into a U. Tie the ends of the two strings to one arm of the U. Then tie the other ends to the other arm. Make sure that the longer part of the reel is towards the top and the holes are near the bottom.

4. Of course, this doesn't look like a Break-dancer yet. Paint a face and body on the reel or make a head, hands and legs of chart paper and glue them on to the reel.

What it does

Gently press the two sides of the U together and release them. The Break-dancer flips over, performing amazing feats.

When it doesn't

Is the string stretched tightly enough? If it is loose, the dancer falls sloppily and does not flip over. Check again if the holes are near the base of the reel.

If you are using a bamboo stick, use the outer layer of the bamboo. It bends easily because it is fibrous and flexible. The inner part has short fibres and snaps in two when you try to bend it.

Thirst Prize

Instead of an acrobat, make a crow with a long neck. To do this, all you have to do is attach two more reels on top of the first one. You could glue them on, or easier still, wedge a roll of paper into the first one, leaving a bit of the roll jutting out. Then push the next reel over the part that is sticking out. Do the same with the third reel. To make the whole thing look like a crow, add a beak and a tail. You could also paint it black, if you are particular. When you press the U-shaped stick, the crow dips its head.

Now fill a bottle-cap with water and place it on the floor. Let each of your friends try to make the crow drink the water. The one who does it in the least number of tries wins the game.

The winner gets a glass of water - as thirst prize.

Centre of gravity

The reel is held up because of the tension (T1 and T2) in the strings. The weight of the reel acts downwards at the centre of gravity. When you press the two sides of the stick, the tension acts on the strings again. The tension along the upper string pulls the lower part of the reel upwards and the tension along the lower string pulls the upper part downwards. The reel flips back into its initial position.

Try

Traditionally, this toy was made of shola-pith, a light but firm material found inside the stems of some plants. You could use wooden ice-cream spoons, glued together, with the strings passing between them.

Think

The "Law of Conservation of Energy" states that energy can neither be created nor destroyed. How is this law applied in the Break-dancer?

Hint:Elastic energy or tension is converted to kinetic energy and vice versa.

What would happen if the two holes were near the top of the reel? Would the Break-dancer dance then? And what if the holes were exactly at the centre of the reel?

Hint: When an object is not balanced, it tries to reach a position at which its centre of gravity is the lowest.

SUDARSHAN KHANNA

GITA WOLF

ANUSHKA RAVISHANKAR

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