Science corner

16th May 2003 at 01:00
Through thick and thin: Sophie Duncan looks at ways of measuring viscosity.

Oil and water have very interesting properties and make great materials for science activities. Try these with your students to explore properties of density and viscosity.

Take a couple of jars with lids. Baby food jars work well. Fill one with golden syrup and one with water. Do not completely fill the jars, but leave a small air bubble. Turn each of the jars over and watch how quickly the air bubble moves.

Now put the jars in the fridge for 30 minutes and repeat the experiment.

Finally, stand the jars in a dish of hot water for five minutes and try the experiment again.

The speed with which the bubble moves depends on the viscosity of the fluid inside the jar. Viscosity is a measure of how easy it is to move a liquid, and the viscosity of a liquid depends on its temperature. As the liquid gets hotter it becomes less viscous.

You can follow up this experiment by trying lots of other types of liquid, such as honey, ketchup or shampoo.

Take a number of narrow jars and fill them with the different liquids. Make a line five centimetres from the top of each jar. Put a marble or a piece of chocolate into the jar and time how long it takes to move from the line to the bottom. You can make a graph of your results.

A different activity looks at the difference in density of water and ice.

Make some coloured ice cubes. Give each of your students a small glass three-quarters full of oil. Ask them to place an ice cube into their glass and observe what happens.

The ice should float as it is less dense than oil. As the ice cube melts the water will sink to the bottom of the glass as it is denser than oil.

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

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