# Marching model of refraction

##### Class Practical

A kinesthetic experience of refraction can help students to understand and remember what happens to wavefronts.

#### Apparatus and materials

Hard road with straight boundary adjoining soft grass, (alternatively, areas of asphalt marked with chalk can be used)

Small army of students

Discipline

#### Procedure

a Students must first learn to march in step, with a uniform pace and then learn to change to steps half as long with the same frequency. Like a drill officer, count out ‘left-right, left-right’ until they are able to march in both ways.

b Align the army in fours or sixes, each tier with linked arms to imitate consecutive wavefronts. Then let them march on the road meeting the boundary obliquely. As soon as each crosses the boundary s/he must change to steps half as long. This will produce a change in direction of each wavefront, demonstrating refraction towards the normal.

c You may want to try the experiment again, with students marching from the grass to the road: refraction away from the normal will occur.

#### Teaching notes

This does take time to practise, but students are likely to enjoy it and so understand and remember why waves are refracted. On a wet day you could do this indoors, perhaps in a school hall or gymnasium.

You could also make the army march through a converging 'lens' drawn on the ground: the focal point becomes a pile-up of confusion.

Ed: We improved the text to this experiment following a comment from Robert Friedman.

This experiment was safety-checked in February 2006