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IB DemystifiedMYP Sciences

Sound and hearing

Every sound you hear, from birdsong to a motorbike horn, starts with something vibrating. Sound travels as vibrations passed from particle to particle until it makes your eardrum vibrate, and very loud sounds can damage your hearing for ever.

Recommended for MYP 1 · About 3 lessons · Criteria A, B, C and D

A: originalB: louderC: higher pitchSame screen settings for all three. Height = amplitude; number of waves across = frequency.
Figure 1. The amplitude of a sound wave shows its loudness; the frequency shows its pitch.
On this page
  1. Learning objectives
  2. Before you start
  3. Key vocabulary
  4. Understanding the ideas
  5. Pitch and loudness
  6. Sound in the real world
  7. Worked examples
  8. Assessment tips
  9. Check your understanding
  10. Practice questions
  11. Investigation
  12. Criterion-linked questions
  13. Challenge questions
  14. Topic check
  15. Review your mistakes
  16. Your progress

Learning objectives

By the end of this topic you should be able to:

  • explain how sounds are made and how they travel
  • relate pitch to frequency and loudness to amplitude
  • describe how the ear works and how hearing can be damaged
  • explain echoes and uses of sound such as ultrasound
  • analyse sound data and plan fair tests
  • discuss noise pollution and safe listening

Before you start

You will use these skills. If any feel shaky, review them first.

  • particles in solids, liquids and gases (see States of matter)
  • energy transfers (see Energy stores and transfers)
  • multiplication and division

Key vocabulary

Vibration
A rapid back-and-forth movement.
Frequency
The number of vibrations per second, measured in hertz (Hz); it sets the pitch.
Amplitude
The size of a vibration; it sets the loudness.
Decibel (dB)
The unit used to measure sound level.
Echo
A sound reflected from a surface.
Ultrasound
Sound too high-pitched for humans to hear (above 20 000 Hz).

Understanding the ideas

  1. What is it?

    Sounds are made by vibrating objects. The vibrations are passed on through a medium (a solid, liquid or gas) as particles push on their neighbours. Sound cannot travel through a vacuum, and it travels faster in solids than in liquids or gases.

  2. Why does it happen?

    Faster vibrations have a higher frequency and a higher pitch; bigger vibrations have a larger amplitude and are louder. Humans can hear roughly 20 Hz to 20 000 Hz.

  3. How do we know?

    We can see sound waves using a microphone and an oscilloscope, and measure loudness with a sound meter in decibels. In the ear, the eardrum and three tiny bones pass vibrations to the cochlea, whose hair cells send signals to the brain.

  4. Why does it matter?

    Echoes are used by bats, ships and doctors (ultrasound scans). Loud noise above about 85 dB can permanently damage hearing, so noise limits and ear protection matter.

  5. What does it connect to?

    Sound links to waves, energy and light in physics, and to the ear, nerves and animal senses in biology.

Pitch and loudness

  • Pitch depends on frequency: faster vibrations give a higher pitch (shorter, tighter or smaller vibrating objects).
  • Loudness depends on amplitude: bigger vibrations give a louder sound.
  • On an oscilloscope: taller waves = louder; more waves across = higher pitch.
  • Speed of sound: about 340 m/s in air, about 1500 m/s in water, about 5000 m/s in steel.

Sound in the real world

Doctors use ultrasound to check on unborn babies. Ships use echo sounding to measure the depth of the sea. Traffic police in busy cities are exposed to high noise levels every day, which is why some cities have banned pressure horns.

Worked examples

Example 1: an echo

A shout echoes back from a wall after 0.5 s. How far away is the wall? (Speed of sound = 340 m/s)

  1. Total distance = 340 × 0.5 = 170 m.
  2. This is there and back, so the wall is 170 ÷ 2 = 85 m away.

Example 2: reading waves

On an oscilloscope, sound X has taller waves than sound Y, but the same number of waves. Compare them.

  1. Taller waves mean a bigger amplitude, so X is louder.
  2. The same number of waves means the same frequency, so the same pitch.

Assessment tips

Sound questions often use oscilloscope traces and simple calculations. Expect to:

  • Explain how sound is made and travels.
  • Compare waves for pitch and loudness.
  • Calculate distances from echoes (remember: there and back).
  • Discuss noise and hearing protection.

Common mistakes: saying sound can travel through a vacuum; mixing up pitch and loudness; forgetting to halve the distance for an echo; and confusing hertz with decibels.

Check your understanding

Quick questions on the ideas above. Try each one before using a hint.

Practice questions

Show

Investigation: a string telephone

Partially guided investigation · about 40 minutes · pairs

Research question
How does the type of string (cotton thread, fishing line, wool or thin wire) affect how well a string telephone carries sound?
Scientific background
When you speak into a cup, its base vibrates and passes the vibrations along the tight string to the other cup, which vibrates and makes sound. Some materials pass vibrations better than others.
Hypothesis
Write your own prediction, with a scientific justification.
Variables
Identify your independent, dependent and control variables, and explain how you will control them.
Apparatus
Two paper cups, four different strings of the same length (5 m), sharp pencil, paper clips, a phone sound-meter app.
Method
  1. Make a small hole in the base of each cup, thread the string through and tie it to a paper clip inside.
  2. Pull the string tight and speak at the same volume into one cup.
  3. Measure the sound level at the other cup with the app held in the same position.
  4. Repeat three times for each string and compare the means.

Safety. Take care with the pencil point when making holes. Keep strings away from doorways where people could trip.

Then evaluate: why must the string be kept tight, and what happens if someone touches it?

Criterion-linked questions

Criterion B: inquiring and designing

Criterion C: processing and evaluating

Criterion D: reflecting on the impacts of science

Challenge questions

Harder problems in unfamiliar contexts. Plan before you calculate.

Topic check

Five questions picked at random from the whole topic. Take a new set whenever you like.

Review your mistakes

Questions you got wrong on this device appear here so you can try them again. Answer one correctly and it leaves the list.

Your progress

Tracked separately for each skill, on this device only.

SkillCorrectStatus

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