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Across the pond

Water boatmen, whirligig beetles and DIY pond skaters help make science lessons fun, says Zoe Crompton.

Science

Studying and making a pond skater is a good way for your pupils to find out about different aspects of science and the local environment.

To make the simple pond skater you just need two paper clips. To make a model pond skater you will need small twigs and sticky tape.

For the simple pond skater bend one paper clip so that you can balance a second one on it. Lower the paper clip very slowly into clean water so that it floats; if you are too quick it will sink.

For the model pond skater carefully bend the twigs to make the pond skater's legs. Use a branching twig or join legs together with small pieces of sticky tape.

Make sure the pond skater's legs are all the same length. Cut four 1cm pieces of sticky tape for the pond skater's feet. Use small pieces of sticky tape to attach the feet to the twig legs so the sticky tape of the feet is sticky side out.

Your pond skater is ready to try out on a bowl of water. (Store it on its back or the sticky feet will get stuck.)

It's good to ask the children questions to get them thinking. These might include:

- What will happen when I lower the paper clip on to the water?

- What would happen if I dropped a paper clip into the water?

- What will happen if you touch the floating paper clip?

Get them to look closely at the model pond skater's feet. What do they do to the surface of the water? How could they improve the pond skater?

You can take this lesson further. If you have a school pond you may see pond skaters on the surface, as well as whirligig beetles and water boatmen. Children could find out about other animals that live in the pond and make more models.

Gifted and talented children could use books and the internet to find out more about how the animals are adapted to life in a pond.

Add a drop of detergent to the water and you will break the surface tension and your pond skater will sink.

How does Dash from The Incredibles run on water? His technique is very similar to a basilisk that runs too fast to sink, rather than a pond skater that is very light and does not break the surface tension.

Imagine what life is like for shrunken humans living in the pond with the pond skaters and use a tape recorder to record a story about their adventures

Zoe Crompton is a professional development leader at the National Science Learning Centre. For more information visit www.sciencelearningcentres.org.uk

Skating on the surface

How does the science work?

Water surface tension is like a rubber skin to water. You can see surface tension when water forms a ball on leaves and flowers after it has rained. To show surface tension, carefully overfill a plastic cup or drop water on to velvet or fur and it stays in a ball.

Pond skaters are very light and have tiny hairs on the bottom of their feet. This means that they make a dimple in the surface of the water without breaking the surface tension. When they want to move they row through the water, the dimples are like the oars of a boat.

What skills does this activity develop?

- Problem solving.

- Questioning and reasoning.

- Observation skills.

- Communication skills.

For interactive activities on plants and animals in the environment visit:

bbc.co.ukschoolsscienceclipsages6_7plants_animals_env.shtml

For ideas on pond dipping visit: web.ukonline.co.ukconkerpond-dip

Amazing fact

- The biggest pond skater is the giant Vietnamese water strider, which is 20cm long.

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