Science corner

3rd March 2006 at 00:00
Ray Oliver explains how to create some particle patterns

The particle nature of matter has been of interest to scientists for generations. Van Leeuwenhoek, who developed the use of the microscope, identified particles in the blood he called corpuscles.

Isaac Newton used the same word to describe light. He believed corpuscles of light were material particles travelling at high speeds. At key stages 23 we are more concerned with the arrangement of particles in solids, liquids and gases. Providing accessible models for these ideas is beneficial to understanding. Make the study of particles fun.

First you need large numbers of spherical objects to represent particles.

These can be marbles, golf balls or table tennis balls. Talk about the arrangement of particles in solids, that we believe the particles are in fixed positions and make a regular pattern.

Evidence comes from snowflakes and cubic salt crystals. The interesting question is: how do these regular three-dimensional arrangements, called lattices, arise? Cut a strip of cardboard and fold into a triangle. The side length of the triangle should be about six diameters of the "particles". Using a jug, pour the particles steadily into the triangular shape.

Although a lot just roll away, a three-dimensional pattern gradually builds up, representing the growth of a crystal. This is similar to what happens when a solution of salt water evaporates. Using an overhead projector, add one layer of particles to a transparent dish. It is obvious that the particles pack closely together in lines, in a regular pattern. Adding a few particles of a larger size gives a model of an alloy such as bronze. In an alloy, the particles cannot slip past each other so easily, and these tend to be stronger materials.

Use a large sheet to model what happens when a liquid warms up and evaporates. Add some table tennis balls and get a group to stretch the fabric horizontally. Start to shake the fabric up and down and watch the particles. The more heat energy there is, the more they move and some will escape.

Ray Oliver teaches science at St Albans Girls' School, Hertfordshire

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