Making links - a fundamental part of physics

Making links explicit: fitting representations together

One of the distinctive features of physics as a subject is that it involves representing ideas and phenomena in a whole range of different ways. This is certainly the case in the topic area of radiation.

Think, for example, about the different ways we talk and think about sound:

• Sound waves have a velocity, a frequency, and an amplitude. All three can be measured.
• Sounds need a medium to pass through.
• Sound waves consist of groups of particles oscillating back and forth.
• Sound waves belong to the family of longitudinal waves.
• Sound provides a pathway by which energy can be shifted.
• Sound waves can be represented in terms of graphs that show the variation in density of the air through which they are passing.

This list captures just some of the distinctive features of sound waves: sometimes on a macroscopic scale (the speed is 330 metre inverse second); sometimes on a sub-microscopic scale (picturing the air particles moving back and forth); sometimes in terms of energy; and sometimes graphically.

A deep understanding of sound waves involves being able to fit all of these representations together in such a way that they all make sense. This is often not easy. Students are likely to need help from their teacher in making these key links, and in drawing attention to the nature of the explanations and representations that are currently being used:

Teacher: OK! Let's get those atomic spectacles on and try to picture what is happening in the sound wave in terms of the air particles.

The next step on from making links within the topic area of sound is to start identifying the links (similarities and differences) with other radiations, such as light.

Odd as it may seem, knowing how light and sound radiations differ from each other is a big help in appreciating the key features of each.