Energy and Sound

  • How does sound travel from where it is made to where it is heard?
  • How can we make loud or soft sounds?
  • How can we make low or high sounds?
  • What is noise pollution?

For this chapter, keep the musical instruments which were made by the learners in the previous chapter on display in the classroom. You can then use these instruments to demonstrate various concepts in this chapter. Alternatively, this chapter could be done before the chapter on "Movement and Energy in a System" where a musical instrument is made as this chapter deals with a lot of concepts and investigations into sound that can then be explored when making the musical instrument. Or else, if you are doing this chapter now after making a musical instrument, then use what they first experienced by investigating hands-on when you now deal with the theory.

Vibrations and sound

We have seen that musical instruments make sounds through vibrations. You saw in the previous chapter that when you plucked the strings on some instruments the strings vibrated and made sound.

We can hear and feel vibrations

We know that vibrations cause sound. But can sound can also cause vibrations?

Observing vibrations


  • adeep glass dish
  • cling film
  • some rice grains (or any other small, dry particles)


Part A:

  1. Cover the bowl with the cling film.
  2. Make sure it is tightly covered, but not too tight to start tearing.
  3. Put the rice grains between the middle and the edge of the cling film.
  4. Tap the cling film lightly. Do this away from where you put the rice grains.
  5. Now tap it harder.
  6. Do you see that your rice grains are moving or jumping up and down?

Part B:

Can you get the rice grains to jump using just your voice? When they jump you know the cling film is vibrating.

  1. Hum over the bowl. Near the cling film but away from the rice grains.
  2. Make your voice deep and try again.
  3. Make your voice high and try again.
  4. Hum louder. Hum softly.
  5. Try SHOUTING, but do not blow on the cling film or the rice. Your sound must make the rice jump about, not your breath.


What happens to the rice grains when you tap the cling film?

The rice jumps when the cling film moves.

When you hum, the cling film vibrates. Explain why there is a vibration.

The cling film vibrates because of the sound waves traveling through it make it vibrate.

So what did we learn from this activity?

  • Tapping the cling film gives it energy to vibrate.
  • The rice grains are only there so we can see the vibrations. They do the job well!
  • Making a sound near the cling film causes the rice grains to move.
  • This means the cling film is vibrating from the sound.
  • Sound causes vibrations that you can see.

Can we feel vibrations too? Let's find out!

How do we make sound when we talk or sing?


  1. Rest your hand gently on your neck and hum.
  2. Make low humming sounds and higher humming sounds.
  3. What do you hear?

  4. What do you feel?

There is a vibration in your throat when you hum which you could feel with your hand. It causes the sound you make when you speak and when you shout and when you sing.

What is vibrating in your throat? You have vocal cords in your throat. As air moves over them they vibrate. As they vibrate they cause sound. Look at the picture below. The vocal cords are almost like the layer of cling film over the bowl in the previous activity which vibrates.

Can you see the vocal cords which vibrate to make a sound when we talk or sing?

So we make sounds when our vocal cords vibrate, but how do we hear sounds? In your ear you have eardrums. Eardrums helps us to hear the sound. Your eardrum acts like the cling film. Your eardrums vibrate when a sound goes into your ear. This is how you hear sounds!

The human ear is actually made of many small parts! Your outer ear is what you can see on the sides of your head. Your inner ear is inside your skull and made of small bones. Look at the picture below. Can you see the eardrum which vibrates? This vibration then bumps the little bone next to it and the brain can read this as a sound.

Wow, that all sounds quite complicated! And it's all happening in both my ears every time I hear a sound!

That's right Jojo, the human body is amazing!

Vibrations travel through a material

Sound vibrations need a material to travel through. We call this material a medium. When you are listening to your teacher talk in class, the sound vibrations are travelling through the air to your ears.

How does sound travel through air?

The following idea seems quite tangible... just letting the kids "move" to experience how the vibration is transmitted from one place to another by vibrations of the air is valuable. This interpretation requires no mention of waves. Sound waves are only introduced in the later grades. This activity can help to entrench most of the ideas developed so far (vibrations, how energy gets from one place to another etc) in a tangible way.


  1. Get a group of your friends and stand in a straight row.
  2. Stand side by side all facing the same way. Your shoulders must not touch, but you must be close
  3. Each one of you is an air particle.
  4. Two more friends must stand at the ends of the row. One friend is a vocal cord. The other friend is the eardrum
  5. The 'vocal cord' must bump the first 'air particle' and move back and stand still.
  6. The first 'air particle' must bump the second 'particle' and then move back and stand still.
  7. The second air 'particle' must do the same to the third and move back and stand still and so on...
  8. When the last air particle bumps the eardrum, the eardrum moves and then stand still

So sound is able to move from where it is made to where it is heard by air particles vibrating and passing the vibration from one particle to the next particle.

But does sound travel through other materials?

Making a telephone

This activity can also be done as a class demonstration and you only need to make one telephone instead of each pair making one. This activity and the next one on tapping and listening through the wall demonstrate the same concept. So, if you do not have time to do both, then just perform one of them.


  • two old tin cans or two yogurt containers (ask an adult to make sure the tin cans have no sharp edges that might cut someone!)
  • some string (2 to 5 m long)


  1. Work in pairs.
  2. Ask your teacher to make a small hole at the bottom of each of the tins. You want to connect the two tins with the string.
  3. Tie a big knot at one end of the string, and make sure that the knot is bigger than the hole in the tin.
  4. Pull the string through the hole in one of the tins. The knot must be on the inside of the tin.
  5. Feed the other end of the string through the hole in the other tin. Feed it from outside the tin.
  6. Tie a big knot at the end of the string.
  7. Now you have a funny sort of telephone!
  8. Get a friend to hold one tin to his or her ear.
  9. Take turns to speak into the tin and listening to your friend speak to you.


  1. Why does this tin-telephone work? How does the sound you make get to your friend? After discussing this in class, write down your answer below.

The sound travels along the string. It also travels through air, but its not the same as the sound travelling through the string. The conclusion is that sound exists only in a medium, and it travels better through the string than through the air. For interest, a quick discussion about sound in space: sound cannot travel in space even if vibrations occur - there is no medium for it to move through. Here, sound is carried in three stages: through the air from the vocal cords to the base of the tin; through the string from the base of the first tin to the base of the second tin; through the air from the base of the second tin to the eardrum. A rich and valuable class discussion can evolve from asking how exactly the vibration energy of the speaker's vocal cords ends up as vibration energy of the hearer's eardrum.

Let's do another fun activity to see how sound travels through other mediums!

Secret code through a wall


  1. Work in pairs.
  2. Make up a secret tap code: maybe three quick taps means hello. You can make up words using taps.
  3. Sit on opposite sides of a wall with your partner.
  4. Put your ears to the wall and talk with your tap code through the wall.
  5. You may have to knock if tapping is too soft.
Sit on opposite sides of a wall and communicate to your friend!

Let's summarise what we have learnt about sound and how vibrations move:

  • Sound must travel through something.
  • Your voice can travel through air.
  • Your voice can travel through string.
  • The tapping sounds can travel through a wall.
  • We say that sound needs a medium to travel through.
  • The medium your voice travels through is air.
  • Sound travels through wood and bricks.
  • Sound travels very well in solids.

Why does sound travel well through solids?

This might be hard for learners to answer as it has to do with the arrangement of particles in solids and gases. It is because the particles in solids are close to each other. In gases they are quite far apart compared to solids. This is why solids can carry sound energy better and further than gases.

Whales communicate (talk to each other) under water even when they are very far from each other. Explain how the sound that one whale makes travels to another whale.

The whale causes the particles in the water to vibrate. As water particles are close to each other, the vibrations can move from one particle to the next and the sound can travel through the water.

What happens when there is no medium? If you are able to watch the video of a bell ringing in a vacuum, then do so. Sound needs a medium to be able to travel. A vacuum is where there is no air or any other matter. So do you think you will be able to hear a bell ringing in a vacuum?!

As an extension, if you are able to watch the video, then it shows a bell ringing in a vacuum. First the bell is in a jar that is full of air. We can hear the bell ringing. Slowly, the air is pumped out of the jar by the vacuum pump. The bell sounds softer and softer until you can't hear it all. Explain the observations: Initially there is air in the jar so the vibrations from the bell can be carried through the air by one particle of air causing the next particle of air to vibrate. Once the air has been removed, the bell can't cause anything to vibrate so the sound cannot be carried from the bell to your ear.

Can sound travel from the Moon to the Earth?

No. There is no air between the Moon and the Earth - no molecules of anything to act as medium.

Making sounds

Sometimes you need to speak softly when you whisper a secret to a friend. But other times you need to shout loudly to your friend on the other side of the playing field! Sounds have different volumes.

Also, a mouse makes a very squeaky, high sound. But a lion makes a low growl. The sounds that these animals make have different pitches.

Let's make sounds with an elastic band

This activity can also be done as a demonstration. Instead of cutting the elastic bands, it can be pulled over a lunch box. Pulling it tighter or more loosely will change the sound. You can also use elastic bands of different thickness to produce different sounds.


  • The biggest elastic or rubber band you can find (a hair band will not work very well)


  1. Work in pairs.
  2. Cut your elastic band in one place to make one long elastic strip.
  3. One partner must hold the elastic at both ends.
  4. The other partner can pluck the elastic to make it move.
  5. Try to make loud and soft sounds with your elastic.
  6. Try to make high and low sounds as well. (High sounds are squeaky like a mouse, low sounds are deep like a lion's growl.)
The elastic makes a sound when it moves.


  1. Describe how you made the sound loud.

  2. Describe how you made a high sound.

  3. Describe the movement of the elastic band.

The teacher should emphasise here that the we get different types of movement - running, riding a bicycle, water flowing, clouds blown by the wind. Teach learners that the movement made by the elastic is another type of movement that we call vibration and that this vibration causes sound.

In this activity we have seen that movement causes vibration that causes sound. Different types of movement cause different sounds.

  • When the elastic is plucked (pulled) hard, the sound is loud. You can see the elastic makes big movements.
  • When it is plucked gently (pulled just a little) the sound is soft. You can see the elastic band makes small movements.
  • When the elastic is looser and your partner's hands are closer together, the sound has a lower pitch. Did you see the elastic move slower?
  • When the elastic is tighter and your partner's hands are farther apart, the sound has a higher pitch. Did you see the elastic move quicker?

What we have learnt about volume:

  • Soft sounds are caused by small vibrations.
  • Loud sounds are caused by big vibrations.

What we have learnt about pitch:

  • Ahigh sound is made by fast vibrations.
  • A low sound is made by slow vibrations.

Use some of the instruments made by the learners to show the difference between loud and soft sounds, for example, hitting softly or loudly on a drum to make small and big vibrations respectively. Or if you have another instrument with different length strings, pluck the strings to show the difference in pitch. The shorter strings will vibrate quicker and therefore produce a higher pitch, whereas the longer strings will vibrate more slowly and produce a lower pitch.

Making a water marimba


  • Six or more glass bottles or jars (they must all be the same kind)
  • Water


  1. Pour a small amount of water into one bottle.
  2. Pour a lot of water into another bottle.
  3. Pour water into the other bottles - all bottles must have different amounts of water as shown in the picture.
  4. Arrange the bottles from the fullest to the emptiest, like in the picture below..
  5. Blow over the mouth of the bottles or tap them with a pencil.
  6. You have made a water marimba!
  7. Try making up a song.
A water marimba


  1. If you hit the bottles with the same strength, which bottle made the highest sound?

  2. If you hit the bottles with the same strength, which bottle made the lowest sound?

  3. Compare the sound made by the same bottle when you tap it gently or tap it hard.

Tapping gently makes a soft sound. Tapping hard makes a loud sound.

What did we learn from our water marimba?

  • The height of water in the bottle changes the pitch of the sound made.
  • When you tap a bottle gently or hard, you change the volume of the sound.

How can we make sounds louder? Have you ever seen someone talking over a megaphone? A megaphone makes our voices louder and travel further. Let's make our own megaphone.

Make a megaphone

This activity can also be done as a class demonstration. Each child does not need to make one.


  • thin cardboard or stiff paper
  • sticky tape
  • a pair of scissors


  1. Roll the card or paper into a funnel shape. There must be a hole at the narrow end (about 5cm wide).
  2. Tape the card so that the funnel will keep its shape.
  3. Neaten up the funnel. Use the pair of scissors to cut off any pointy bits at the two open ends.
  4. If you have some extra paper you can make a handle for your megaphone. Decorate your megaphone.
  5. Now you can speak or sing through the small opening.
  6. Test the difference if you speak normally or into the megaphone.
Speak into your megaphone like this.


The megaphone (also called a loudhailer) makes your voice sound louder. How do you think it does this? Discuss this as a class and write an answer down.

This can be quite tricky for learners to answer by themselves so do it as a class discussion. This presents a good opportunity to allow a bit of reasoning to take place in these discussions. There is a paradox to be resolved: louder sounds mean more sound energy reaching your ears, but if you speak in the same way with and without a megaphone, the sound must have the same energy. The idea is that the sound is reflected from the internal walls of the funnel and projected forwards towards the large opening. The sound is therefore concentrated in one direction meaning that more of the sound energy travels towards the hearer making it seem louder than it is without the device.

Is your voice really louder or does the funnel shape just make it seem that way?

The funnel makes your voice seem louder.

Many instruments make sounds louder in some way. Wind instruments (tube instruments) use a tube as a funnel to make sounds seem louder, similar to what you did with the megaphone. String instruments do the same, but using a hollow shape.

Making sound louder with a box

This activity can be combined with the elastic band activity earlier on.


  • acardboard shoe box or plastic box (a margarine tub or lunch box will work well)
  • an elastic (rubber) band


  1. Stretch the elastic between your hands and ask a friend to pluck it.
  2. Now pull the elastic band over the box. The elastic must be tight. If it is not tight use a smaller elastic or a bigger box.
  3. Pluck the elastic.
  4. Feel the sides of the box as the elastic vibrates. Can you feel that the box is also vibrating? You may put a few rice grains inside to show the vibration of the box.
The box makes the sounds louder.

Let's summarise what we learnt from this activity:

  • The box makes the sound seem louder.
  • The box vibrates with the elastic.
  • The vibrations of the box make sound inside the box.
  • This makes the sound seem louder.
  • Some musical instruments have a hollow shape.
  • The sound is reflected inside the hollow.
  • The walls of the hollow shape also vibrate as the sound echoes inside.
  • This makes the sound seem louder.

Do you know what an echo is? An echo is when the sound bounces back off a surface and you hear it many times. Look at the following picture.

An echo occurs when sound bounces back off a surface and you hear it again.

Why do you think a guitar has a big hollow base?

This question leads on from the previous activity and from the previous chapter. The hollow base makes the sounds louder when the strings are plucked as the sounds reflect off the walls in the base causing the sound to be amplified as the vibrations are intensified.

Noise pollution

There are many kinds of pollution. Unfortunately, we are familiar with litter lying around the pavements and waste and rubbish in our rivers and dams. This is ground and water pollution.

Litter polluting the side of the road
Look at the pollution in this pond!

Air pollution is when smoke and chemicals end up in the air which means it is not good for us to breathe it in.

Can you see the air pollution in this city which makes it look smokey? This is called smog.

There are other types of pollution as well, including light and noise pollution. Noise pollution is any sound that continues for a long time and is loud, unpleasant or harmful to our ears.

Identifying noise pollution


List five sounds that are very noisy, sounds that can hurt your ears, or just sounds that are difficult to live with.

Teacher to bring 'noise making instruments' to school - pots and pans to bash together, lids of the pots and pans to bash together, repeatedly running nails over a chalkboard, playing a trumpet or other similar instrument without any knowledge of how to do this - all just MAKING NOISE! motor bike revving, loud music, cheering at sports games, aeroplane taking off, formula 1 racing, drilling holes with a drill

Look at the picture of a learner in a very noisy environment. Identify all the sources of noise pollution.
This is a very noisy environment!

People talking, noise from the taxi, people shouting out the taxi, the jackhammer on the pavement, the aeroplane in the sky, the exhaust and hooter from the red car, the music blasting from the stereos in the furniture shop.

List some sounds that are sometimes not noisy, but other times can be noisy.

music from other cars/neighbours, children playing, sports games, car driving, barking dog

Are there any noises at school which you find distract you during class and cause a disruption? This is also noise pollution. Write down some of these, and also some ways which you think your class could minimise the noise pollution in your class.

Can include noise pollution from other learners walking past the classroom outside, perhaps workers or builders are at the school and making a noise, perhaps there are noisy lawnmowers outside. Possible solutions would be to put up signs outside the classroom to tell learners to be quiet when walking down the corridors during lesson time, or working out a solution with the school that the most noisy activities, whether building or lawn-mowing happens outside of lesson time (i.e. in the afternoon).

Role-play about noise pollution

You will have to facilitate this activity with the class. Go through the brief with them and give them time to develop a script. Then give the pairs an opportunity to act out their situation. It is very important to open the situation up to a general discussion. There is usually no clear right or wrong in these matters. Only consideration and respect for others. Sometimes noise is a necessary result of work and sometimes it is a natural result of relaxation activities. Allow the learners to see their own responsibility towards others in a situation, no matter whether they are the noise makers or the noise sufferers.


  1. You are going to role-play a situation where noise may cause a problem. Do this in pairs.
  2. Choose an activity that may be noisy (watching television, playing music, drilling holes with an electric drill, or any other activity you can think of).
  3. One of you must be the person doing this activity. You must have your own reasons for making the noise. You must also have your own ideas about how much noise you are making.
  4. The other person must be nearby. This person feels that the first person is making too much noise. You must have your own ideas about what too much noise is.
  5. Act out a discussion for the class between the two members of the group.

Think about the following:

The person who is making the noise has rights. The person who is complaining also has rights. Can you get along? Can you come to an agreement? Can you make a compromise?

Each person has their own idea about noise. We need to get along with each other. No one likes to feel uncomfortable. Always be aware of the comfort of others. We also need to understand that sometimes noisy activities are necessary. Always remember: what is okay for you may not be okay for someone else.

Loud noise can damage your ears

Noise pollution makes the area we live or work in very unpleasant. Noise pollution can be harmful and cause permanent damage to hearing. Even music that is too loud is noise pollution.

Most outdoor noise pollution comes from construction sites and noise from cars and trucks. If you live near an airport, there is a lot of noise pollution from the sounds made by the aeroplanes.

  • Loud sounds can damage your hearing.
  • Doctors have found that people who work with very loud machinery become hearing-impaired when they are still young.
  • They have also found that loud music can also cause hearing loss. Powerful amplifiers and speaker systems can be bad for your hearing. Headphones playing loud music can damage your hearing.
  • Do not listen to very loud music, especially through ear phones.
  • Some people are born with a hearing problem and they can use hearing aids to help them hear better.
A hearing aid is very small and fits inside the ear of a hearing-impaired person.
A construction worker wearing ear muffs to protect his ears

At times, noise pollution cannot be avoided. Some factories and building sites are noisy places.

Animals can be harmed by noise pollution. A good example is the whale. Whales communicate with each other by making sounds. The sound can travel over long distances through the water from the one whale to the next. When there are lots of ships present, they make additional noise. Water carries these noises very well and very far. This makes it difficult for whales to communicate with each other. This can cause whales to get lost in the ocean.

A racehorse with ear muffs on its ears

Can you see the ears of this racehorse are covered? Why do you think this is so?

This protects the racehorse from noise pollution from the crowd and stadium so that it does not get distracted when racing.

  • Musical instruments make sound through vibrations.
  • Vibrations can be heard and felt.
  • Sound travels away from the moving part that is vibrating.
  • Sound needs a medium (material) to travel through.
  • Sounds can be loud or soft (volume).
  • Sounds can be high or low (pitch).
  • Sound can be unpleasant and harmful.
  • Loud sounds can damage hearing.

Why is sound important to us?

communication, entertainment

You built a 'telephone' with a string joining two tins. Explain how your telephone works.

Speaking in the tin causes the end of the tin to vibrate. This vibration travels along the tight string. The tin at the other end picks up the vibration which allows you to detect the vibrations and hear them

If a sound is made on the Moon, it cannot be heard even on the Moon. Explain why.

Sound needs a medium (material) to be able to travel through. There is no air on the Moon and so vibrations cannot travel.

Whales can talk to each other over hundreds of kilometers in the ocean. Do you think the particles in water are close together like in a solid or far apart like in a gas?

Close together, as the sound can travel far.

When your doctor has to check your heartbeat she uses a special instrument. It is called a stethoscope.
A doctor using a stethoscope

A stethoscope is simply a long tube of air with a membrane on the side that goes on the patient's chest or back. Explain how you think a stethoscope works.

This is a tricky question and learners might need guidance or a hint when answering. The membrane against your chest or back vibrates as it picks up your heart beat. This vibration travels through the air in the tube to the doctor's ears so they can hear the heartbeat.

When you listen to the radio or TV, you can adjust the volume. What happens to the vibrations making the sound when you increase the volume?

vibrations increase in size

What makes some sounds pleasant, while other sounds are unpleasant?

pitch, volume and personal preference

List three jobs where there is loud noise.

jackhammer operator, ground crew for an aeroplane, working in a steel mill, anything sensible

The people doing these jobs are in danger of damaging their hearing. Give them some advice on how to protect their ears.

wear earplugs

Why is the man in the picture below wearing ear muffs over his ears?
A man wearing ear muffs

He is wearing ear muffs as the car he is driving probably makes a very loud noise. Over time, if he did not protect his ears, they could become damaged.

Why is it a health risk to expose yourself and youngsters to loud music?

It damages your ears and affects your hearing forever.