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Summaries · Grade 4 Natural Sciences › Sound: vibration, pitch and loudness
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Sound: vibration, pitch and loudness

Vibration, pitch and loudness, and how the ear sends sound to the brain. Read one part at a time and tap “I know this”. Then test yourself in the quiz.

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High and low

High pitchLow pitch
Short strawLong straw
Thin guitar stringThick guitar string
String tightenedString looser
Bottle with little water (tap)Bottle with lots of water (tap)
A bird chirpingA big bass drum
Rule

Fast vibrations = high sound. Slow vibrations = low sound.

If you blow across the top of the bottles instead, the bottle with the most water gives the highest sound, because there is less air to vibrate.

Short strings sound high, long strings sound low.
Short strings sound high, long strings sound low.
Tap when you could tell someone without looking.

Loud and soft

Big vibrations make a loud sound; small vibrations a soft sound. Rustling leaves are soft. Very loud sounds can damage your hearing, so workers at machines wear ear protectors.

  • To make a sound louder or carry further: hit, pluck or blow harder (bigger vibrations).
  • Cup your hands around your mouth, or speak through a cone (megaphone): the sound then goes in one direction.
  • A hollow box or calabash that vibrates too makes the sound louder, like a guitar’s body or the uhadi’s calabash.
  • A loudspeaker makes sound much louder.
outer earear canaleardrumtiny bonescochleanerve
The parts of the ear.

A string telephone only works when the string is tight: the vibrations travel along the string.

Tap when you could tell someone without looking.

How we hear

Outer earEar canalEardrumThree tinybonesCochleaNerve tobrain
Sound goes step by step through the ear to the brain.

The outer ear collects the sound. The eardrum starts to vibrate, and three tiny bones pass the vibration on. The cochlea looks like a snail shell and is full of liquid. A nerve sends signals to the brain, and that is where we really ‘hear’.

Meerkat tip

The Karoo’s bat-eared fox hears the soft sounds of insects underground with its big ears.

Tap when you could tell someone without looking.

Remember this and test yourself

Remember this: your summary
  • Something must vibrate to make a sound.
  • Pitch is how high or low a sound is: short, thin and tight gives a high sound.
  • Loudness depends on how big the vibrations are; we measure it in decibels (dB).
  • Sound travels through air, water and solids, but not through empty space.
  • The path through the ear: outer ear → ear canal → eardrum → three tiny bones → cochlea → nerve → brain.

Write these points in your book. Read them again the night before the test.

Memory trick

Short, Thin, Tight = high like a little bird. Long, thick, loose = low like a bass drum.

Flash cards · Tap to turn over

Important words

First say what the word means, then turn the card over.

Test yourself · Part 2

True or false?

Read the question and the answer. Is the answer right? Tap True or False.

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