Sound Wave
Light, Sound and Waves

Hearing things - teaching and learning issues

Teaching Guidance for 5-11

The Teaching and Learning Issues presented here explain the challenges faced in teaching a particular topic. The evidence for these challenges are based on: research carried out on the ways children think about the topic; analyses of thinking and learning research; research carried out into the teaching of the topics; and, good reflective practice.

The challenges are presented with suggested solutions. There are also teaching tips which seek to distil some of the accumulated wisdom.

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Think again

Sound Wave
Light Sound and Waves

Think again - about hearing

Teaching Guidance for 5-11 11-14

Pupils' views on how we hear

Our experience tells us that there is not a big variation in the views that children of this age bring to their science lessons. Nevertheless, it is a good idea to probe the understanding of your pupils at the start of any lesson sequence or module.

A worksheet (see below) might be used to probe pupils' thinking on sound, allowing them to show what they understand. Included are the responses of six pupils to the sheet.

See if you can spot any common patterns, things to avoid and things you'd want to reinforce in your teaching.

Resources

Download the support sheet / student worksheet for this activity.

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Sounds and vibrating sources

Sound Wave
Light Sound and Waves

Sounds and vibrating sources

Teaching Guidance for 5-11 11-14

Vibration

Wrong Track: If you hit a cymbal it vibrates to make the sound. If you drop a spoon on the kitchen table it just makes a noise.

Right Lines: All sounds are produced by vibrations. If you drop a spoon on the table, the sound you hear comes from the vibrations that are set up in the table and spoon.

Teaching and learning about vibrations

Thinking about the learning

The challenge here is for pupils to come to appreciate that all sounds are generated by the vibration of a source.

In some situations the vibrating object is obvious; in others it is less so. Where the vibration is less obvious, pupils tend to revert to ad-hoc explanations for the generation of the sound, often focusing on human action. For example, The hammer makes the bang because you hit the wood hard with it. The learning challenge for pupils is to develop the general idea that all sounds are produced by vibrations.

Thinking about the teaching

In your teaching it is worth identifying where the sound is coming from each time you consider a new sound-making context. Take the time to chase down what it is that is vibrating to act as the source of the sound.

A teaching colleague entertains her classes each year with the invitation:

Teacher: Let's play spot the vibration!

She uses a range of examples in class:

  • In a reed instrument (clarinet, saxophone, oboe): the reed vibrates, setting all of the air in the instrument tube vibrating.
  • In a stringed instrument: the strings are first set into vibration, by either bowing or plucking, then air is set in motion in the box behind the strings.
  • In a flute or recorder: the mouthpiece is shaped so that the air striking one edge of it is set into vibration. This small vibration sets up a larger vibration of the air in the instrument tube.
  • When two stones are clinked together: it is the stones that vibrate, changing shape as they do so, much like the surface of a drum.

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Sounds - groups of particles moving to and fro

Sound Wave
Light Sound and Waves

Sounds - groups of particles moving to and fro

Teaching Guidance for 5-11 11-14

The physical nature of sounds

Wrong Track: Sounds travel to your television through the cable from the TV company.

Right Lines: Electrical signals pass down the cable to your television. Here they are decoded and the loudspeaker in the television produces the desired sounds.

Codes are not sounds

Wrong Track: You buy CD sounds at a record shop.

Right Lines: The sound does not just sit on the CD. The code on the CD is read by the CD player, which drives the speakers in the headphones and they produce the sounds (music to your ears!).

The nature of sound in teaching and learning

Thinking about the learning

This learning challenge involves being clear about the physical nature of sounds… what they really are.

The challenge here is for pupils to come to recognise and to understand the scientific view of what sound is: the disturbance created by the source, which travels out through the surrounding medium. The disturbance itself consists of successive regions of high and low-density air created by the forwards and backwards motion of millions of air particles. No to and fro motion – no sound.

Thinking about the teaching

It is worth emphasising the message:

Teacher: If it does not involve the to-and-fro movement of a medium, is is not a sound.

So sound is not stored on a CD; it is not transmitted to a radio set; it is not delivered down a cable to a television.

Sounds can be produced by decoding what is stored on these artefacts. You need to take care to refer to sound only when you want to speak of the to and fro movements of the medium. Sound only exists in each of these cases after the loudspeaker.

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To and fro motion

Sound Wave
Light Sound and Waves

To and fro motion

Teaching Guidance for 5-11 11-14

Vibrating sources

A fundamental property of sound is that it is produced by a source that vibrates. This to and fro motion applies to all sounds, whatever the medium.

Teacher Tip: Regions of high pressure and low pressure happen as a result of to and fro motion in air. (The to and fro causes increases and decreases in the density of the air, thus changing the pressure). Changes in pressure can only happen in fluids; sounds can travel in solids as well. So keep it simple and general: to and fro is both accurate and sufficient.

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What travels and what doesn't travel?

Sound Wave
Light Sound and Waves

What travels and what doesn't travel?

Teaching Guidance for 5-11 11-14

Sound as a disturbance in the air

Wrong Track: The air just in front of the loudspeaker is pushed forward by the cone and it then travels to your ear so that you can hear the sound.

Right Lines: Vibrations travel as the disturbance from the speaker cone spreads out through the air. First of all the air next to the cone is made to move to and fro. Since neighbouring particles affect one another this pattern is passed on to groups of particles all around. So the pattern of vibration travels from one block of particles to the next, and the sound travels without the particles needing to make the trip themselves.

Vibrations travelling

Thinking about the learning

Some children have the idea that sound is an entity that itself travels from speaker to ear. This view needs to be countered with the scientific view that sound is not an object but a process – the travelling disturbance of the medium.

Thinking about the learning

The fact that sound travels through solids, where the particles are restricted to vibrating about fixed positions, provides a good counter-argument to those who think that the particles need to move from source to detector in order to carry the sound.

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Sounds travelling - not just filling

Sound Wave
Light Sound and Waves

Sounds travelling - not just filling

Teaching Guidance for 5-11 11-14

Sound travels

Wrong Track: I had my radio on very loud and the music just filled the house.

Right Lines: Sound travels from the radio to all parts of the house.

Filling or travelling

Thinking about the learning

Some pupils talk about sound as if it is something that can fill a space. Sound can only fill a space to the extent that it travels through that space.

Thinking about the teaching

Each time you talk about sound, try to emphasise the source–medium–detector model, making it the most natural thing in the world to look for paths along which the sound travels.

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Sounds getting softer

Sound Wave
Light Sound and Waves

Sounds getting softer

Teaching Guidance for 5-11 11-14

Sounds dissipating

Wrong Track: Sounds run out as they get farther away from the source, and eventually stop.

Right Lines: The movement (or the energy) from the vibrating source is spread across more and more particles.

Sound energy

Thinking about the learning

Typically pupils are quite happy to say that sounds get quieter as they travel farther away from the source and suggest they die away. Pupils are not concerned with accounting for where the initial motion (or energy) of the vibrating cone and medium ends up.

Thinking about the teaching

One of the ways in which the sound get quieter is that the energy of the vibrations is transferred to more and more particles as the vibrations spread out over a larger and larger sphere.

Imagine throwing a pebble into the middle of a pond, creating waves that spread out over the surface (just like the pattern of high and low density travelling through the air) in an ever-expanding circle. As the circle gets bigger the energy available for each centimetre of the circumference gets less.

Since a sound travels out over a three-dimensional space (rather than a circle), the energy from the source is spread out much more for each centimetre moved away from the source.

In addition, some of the sound may be absorbed by the stuff through which it travels. In this case not all of the vibration of one block of particles is passed onto the next – some of the energy gets spread around, resulting in a disordered jiggling, rather than in the organised vibration of the sound. Materials and structures that do this particularly well are good sound insulators – good at insulating source from detector.

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Light rays but not sound rays

Sound Wave
Light Sound and Waves

Light rays but not sound rays

Teaching Guidance for 5-11 11-14

Don't use the idea of rays in discussing sound

Teacher Tip: Rays are used to model light, but not sound.

Here is why.

In explaining the properties of light we suggest constructing diagrams based on light rays, which are imaginary. Rays can be imagined to represent infinitely thin beams of light.

In optics, light rays are used a lot because real light beams act in much the same way as the model rays. In other words, light really does travel along well defined paths, which do not diverge too much with distance.

Sound does not travel in sharply defined beams. Instead it spreads much more as it goes – beams are very hard to maintain.

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Separating loud/quiet (loudness) from high/low (pitch)

Sound Wave
Light Sound and Waves

Separating loud/quiet (loudness) from high/low (pitch)

Teaching Guidance for 5-11

Frequency and pitch

Wrong Track: There are more vibrations, so it will be louder.

Right Lines: There are more vibrations each second, so the frequency will be higher, giving a higher pitched sound.

Amplitude and loudness

Wrong Track: With bigger vibrations it will be a higher sound.

Right Lines: If the amplitude of the vibration of the source is bigger, the sound produced will be louder.

Describing sound

Thinking about the learning

The central learning challenge for children is for them to develop a clear understanding of the difference between describing sounds in terms of loudness (amplitude) and pitch (frequency). There are two separate ways of describing sounds here, and the aim must be to help children differentiate between them.

Thinking about the teaching

Using terms such as more vibrations or it vibrates more is likely to lead to confusion among your children. Be clear in specifying either.

More vibrations in a second (pitch or frequency) or each vibration involves a greater to-and-fro movement of the source, or of the air (loudness or amplitude)

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Speed of sound: speed of light

Sound Wave
Light Sound and Waves

Speed of sound: speed of light

Teaching Guidance for 5-11 11-14

Different speeds of sound and light

Thinking about the learning

Pupils need to differentiate between the speed of sound in air (about 340 metre / second) and the speed of light in air (about 3 × 108 metre / second).

Teacher Tip: Introduce everyday examples to emphasise that sound and light travel at different speeds.

Thinking about the teaching

Many pupils are familiar with the situations that can be referred to in drawing attention to the difference between the speeds of sound and light. For example, they may know that you can see a flash of lightening before you hear the peal of thunder. They may not, however, be clear about how this observation can be accounted for.

We see the flash virtually instantaneously because light travels so fast. Sound, on the other hand, travels more slowly (about 300 metre / second). If the storm is one mile away – about 1500 m – the sound will take about 5 s to arrive.

Other situations that you might talk about with pupils include:

Sprinters start on the flash of a gun, rather than the bang. On school sports day, the starter actually stands half way down the 100 m track with the starting pistol. How long will it take for the bang to arrive? (About 0.3 s).

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Sounds through solids and liquids as well as gases

Sound Wave
Light Sound and Waves

Sounds through solids and liquids as well as gases

Teaching Guidance for 5-11 11-14

Sounds through solids and liquids

Thinking about the learning

Pupils need to appreciate that sounds can travel not only through gases but also through solids and liquids.

Teacher Tip: Use examples where sound travels through media other than air.

Thinking about the teaching

You can have an interesting discussion with pupils about sounds travelling through solids and liquids. Most of them will be able to tell you that they can still hear muffled sounds while swimming underwater in a swimming pool. They may have seen TV or films in which submarine crews are able to hear the sound of the engine on a passing ship. Some may have played at passing messages down iron railings by tapping one end and getting a friend to put their ear next to the railing at the other end.

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