Chapter 1 of 8

All 8 chapters
  1. 1Sounds come from vibrations, readunderstood
  2. 2Sound travels, readunderstood
  3. 3Echoes, readunderstood
  4. 4A string telephone, readunderstood
  5. 5Loud and quiet, readunderstood
  6. 6High and low notes, readunderstood
  7. 7How we hear, readunderstood
  8. 8Noise and our ears, readunderstood

S2.7.1 Chapter 1

Sounds come from vibrations

What is happening when something makes a sound?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

By the end you can

  • Show that a sound is made when something vibrates
  • Show vibrations with rice grains on a tin or tight paper

Pluck a rubber band. You hear a sound. What made it?

To vibrate is to move back and forth very fast. This fast movement is a vibration.

Every sound comes from something that vibrates.

Draw it first

Draw how a plucked string makes a sound

  1. A string stretched between two posts, labelled string. Dashed lines show the string bent up and bent down, labelled back and forth. Three arrows point away from the string, and the word sound sits below them.string

    1 Draw two posts with a tight string between them. Write string.

  2. A string stretched between two posts, labelled string. Dashed lines show the string bent up and bent down, labelled back and forth. Three arrows point away from the string, and the word sound sits below them.stringback and forth

    2 Pluck it. Draw dashed lines for where the string goes up and down. Write back and forth.

  3. A string stretched between two posts, labelled string. Dashed lines show the string bent up and bent down, labelled back and forth. Three arrows point away from the string, and the word sound sits below them.stringback and forthsound

    3 Draw arrows going out from the string. Write sound.

You can see a plucked string blur. It moves too fast to follow.

A drum skin vibrates when you hit it. A string vibrates when you pluck it.

A drum seen from the side, labelled drum. Its skin is a straight line across the top, labelled drum skin. Dashed lines bend up and down from the skin, and the word vibration is written beside them.drumdrum skinvibration
The drum skin moves up and down very fast.

A ruler can show it too. Press one end flat on a table. Let the other end stick out.

Flick the free end and keep it away from your face. It buzzes up and down. That is a vibration, and you can hear it.

A ruler lies on a table, labelled table. An arrow labelled hold down presses on the part over the table. The other part sticks out past the table and is labelled free end. Dashed lines show the free end bent up and bent down, and the word vibration is written beside them.hold downfree endtablevibration
The held part cannot move. The free end vibrates.

Your voice works the same way. In your neck is your voice box. It vibrates when you talk.

Put your fingers on your throat. Hum a long note. You feel a buzz. That is your voice box vibrating.

A head and neck seen from the side. A small circle in the neck is labelled voice box. Three short bent marks beside the neck are labelled buzz.voice boxbuzz
Your voice box vibrates, and your fingers feel the buzz.

See it three ways

As a picture

A drum on the left, labelled drum, with a stick on top of it. Short shake marks sit between the drum and a wavy line. The wavy line goes out to the right and is labelled sound.drumsound

In words

A hit drum skin vibrates. The vibration travels out as sound. When the skin stops, the sound stops.

Try it

See a sound shake rice

You need: a bowl or a tin with no lid, a sheet of thin paper or a clean plastic bag, string or a strong rubber band, a spoonful of rice, or sand or salt, a pan and a spoon.

Be safe: Never taste or eat the rice from this activity. Wash your hands afterwards.

  1. Stretch the paper tight over the bowl. Tie it with string so it stays tight.
  2. Sprinkle the rice on the paper.
  3. Tap the paper gently with one finger. Watch the rice.
  4. Hold the pan close above the paper. Hit the pan with the spoon. Watch again.
  5. Now hit the pan harder. Does the rice jump more?

What you will see: The rice grains jump and dance. They jump more with a louder sound. The sound makes the paper vibrate, and the paper shakes the rice.

If you cannot try it, this is what happens.
A bowl with a sheet of paper stretched tight across its top, labelled bowl and paper. Small round rice grains, labelled rice, are jumping up from the paper.ricepaperbowl

A wrong idea many people have

Nothing moves when a sound is made.

Why it feels right: A drum looks still when it sounds. You cannot see the shaking.

The test that breaks it: Do the rice test. The paper looks still, but the rice jumps. Or put your fingers on your throat and hum. You feel the buzz. Stop humming and the buzz stops too.

What is true: Every sound comes from something that vibrates. The movement is too fast and too small to see.

Key words

vibrate
to move back and forth very fast.
vibration
the fast movement back and forth.
voice box
the part of your neck that vibrates when you talk.

Back to your guess

The answer is B: Something shakes back and forth very fast.

Something shakes back and forth very fast. That shaking is a vibration. Every sound starts with one.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. What makes a sound?

    Tap your answer.

    1. Not this one. A still thing makes no sound. A sound starts when something moves back and forth. Try another.

    2. Not this one. Warmth does not make a sound. A vibration does. Try another.

    3. Yes, that is right. Every sound starts with a vibration. A drum skin, a string or a voice box all vibrate.

    See the answer

    Something that vibrates

    Every sound starts with a vibration. A drum skin, a string or a voice box all vibrate.

    • If you chose A: A still thing makes no sound. A sound starts when something moves back and forth.
    • If you chose B: Warmth does not make a sound. A vibration does.

  2. You hum with your fingers on your throat. What do you feel?

    Tap your answer.

    1. Yes, that is right. Your voice box vibrates when you hum. Your fingers feel the vibration.

    2. Not this one. Your voice box vibrates when you hum. Your fingers feel it. Try another.

    3. Not this one. No air comes out through the skin of your throat. The buzz you feel is your voice box. Try another.

    See the answer

    A buzz from my voice box

    Your voice box vibrates when you hum. Your fingers feel the vibration.

    • If you chose B: Your voice box vibrates when you hum. Your fingers feel it.
    • If you chose C: No air comes out through the skin of your throat. The buzz you feel is your voice box.

  3. Rice jumps on tight paper when you hit a pan close by. Why?

    Tap your answer.

    1. Not this one. The paper looks still, but it vibrates too fast to see. That moves the rice. Try another.

    2. Yes, that is right. The vibration is too fast to see. The rice grains show it.

    3. Not this one. The rice did not make the sound. It was moved by the paper. Try another.

    See the answer

    The sound makes the paper vibrate, and the paper shakes the rice.

    The vibration is too fast to see. The rice grains show it.

    • If you chose A: The paper looks still, but it vibrates too fast to see. That moves the rice.
    • If you chose C: The rice did not make the sound. It was moved by the paper.

  4. A guitar string is plucked. What does the string do?

    See the answer

    It moves back and forth very fast. This makes a sound.

    A plucked string vibrates. The vibration sends out sound.

  5. Draw a plucked string. Show how it moves.

    See the answer

    A string between two posts. Dashed lines show it bent up and bent down.

    A string moves back and forth. The dashed lines show the two ends of its movement.

  6. Kofi hits a drum, and it sounds loud. He then lays his hand flat on the skin. What happens to the sound?

    Tap your answer.

    1. Not this one. Every sound needs a vibration. Hold the skin still and the sound stops. Try another.

    2. Not this one. His hand holds the skin still. A still skin cannot make a sound. Try another.

    3. Not this one. A hand does not store sound. The skin stops vibrating, so no sound is made. Try another.

    4. Yes, that is right. A sound lasts only while something vibrates. A hand on the skin stops the vibration.

    See the answer

    It stops, because the skin cannot vibrate.

    A sound lasts only while something vibrates. A hand on the skin stops the vibration.

    • If you chose A: Every sound needs a vibration. Hold the skin still and the sound stops.
    • If you chose B: His hand holds the skin still. A still skin cannot make a sound.
    • If you chose C: A hand does not store sound. The skin stops vibrating, so no sound is made.

  7. Look at the picture. Joseph presses one end of a ruler and flicks the other end. Which part vibrates?

    A ruler lies on a table, labelled table. An arrow labelled press points down onto the part over the table, which is marked P. The other part sticks out past the table and is marked Q. Labels: press, table, P, Q.presstablePQ
    Tap your answer.

    1. Not this one. The part pressed on the table is held still. It cannot move. Try another.

    2. Not this one. A solid can vibrate too. The free end moves up and down very fast. Try another.

    3. Yes, that is right. The free end is not held, so it moves back and forth. That vibration makes the buzz.

    See the answer

    The free end, Q

    The free end is not held, so it moves back and forth. That vibration makes the buzz.

    • If you chose A: The part pressed on the table is held still. It cannot move.
    • If you chose B: A solid can vibrate too. The free end moves up and down very fast.

  8. Lucía plucks a guitar string and sees a blur. What is the blur?

    Tap your answer.

    1. Yes, that is right. The string vibrates. It moves too fast to follow, so it looks blurred.

    2. Not this one. You cannot see sound. You see the string, which moves too fast to follow. Try another.

    3. Not this one. There is still one string. It moves so fast that it seems to be in many places. Try another.

    See the answer

    The string moving back and forth very fast

    The string vibrates. It moves too fast to follow, so it looks blurred.

    • If you chose B: You cannot see sound. You see the string, which moves too fast to follow.
    • If you chose C: There is still one string. It moves so fast that it seems to be in many places.

Keep it

Copy this into your exercise book.

A sound is made when something vibrates. To vibrate is to move back and forth very fast. A drum skin, a string and a voice box all vibrate. Rice on tight paper shows it.

Draw: A string between two posts. Dashed lines for the up and down. Arrows going out.

Reading with a child? A short page for the adult: what this chapter teaches and three questions to ask.

No internet tomorrow? Save the whole book as one file (610 KB). It opens on any phone.