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Grade 3 (age 8-9)

grade 3 Properties of Sound

Put your hand on your throat while you talk, and you can feel it buzzing slightly. Sound is made when something vibrates like this, and the vibration travels through the air to your ears so you can hear it. Fast vibrations make a high sound and slow ones a low sound, while big vibrations make a loud sound and small ones a quiet sound. In the first picture, change how fast a string vibrates; in the second, change speed and size separately and compare how pitch and loudness are drawn.

Sound comes from vibration

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🎵 What sound needs
①Something has to vibrate for a sound to happen
②Pluck a guitar string and the string vibrates; hit a drum and the drumskin vibrates
③The vibrating object pushes and pulls the air around it, and the vibration travels through the air to your ears
④When the vibration stops, so does the sound: press your hand on a ringing drum and it goes quiet at once

Pitch and loudness

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💡 High and loud are different
①The more times something vibrates each second, the higher the sound, and the waves in the picture get closer together
②The bigger the vibration, the louder the sound, and the waves in the picture get taller
③Pitch and loudness change separately, so a sound can be high and quiet or low and loud
④On a guitar, thin strings vibrate fast for high notes, and thick strings vibrate slowly for low notes

Summary

Pitch
Fast vibration → high sound / Slow vibration → low sound
The number of vibrations each second (frequency) sets the pitch
Loudness
Big vibration → loud sound / Small vibration → quiet sound
The size of the vibration (amplitude) sets the loudness
🎯 Key points
①Sound is made by things vibrating
②Fast vibrations make high sounds, and slow ones make low sounds
③Big vibrations make loud sounds, and small ones make quiet sounds
④Sound travels not only through air but also through water, wood, and metal
⑤Where there is no air, as in space, sound cannot travel

Examples and Unit Test

Example 1
Why does a sound happen when you pluck a guitar string or hit a drum?
1
Sound is made when something vibrates.
2
The guitar string or drumskin vibrates, and the vibration travels through the air to your ears, so you hear a sound.
▸ The string or drumskin vibrates, and the vibration travels through the air
Touch a vibrating string lightly and you feel a tickly buzz; grip it tightly and the sound stops.
Example 2
To make a sound higher, and to make it louder, how should the vibration change in each case?
1
The faster the vibration (the more vibrations each second), the higher the sound.
2
The bigger the vibration, the louder the sound. Speed sets the pitch, and size sets the loudness.
▸ Vibrate faster for a higher sound, and bigger for a louder sound
In the second picture, raising the speed packs the waves closer, and raising the size makes them taller.
Unit-test style
Which statement about the properties of sound is correct?
①Sound is made when something vibrates
②The slower the vibration, the higher the sound
③The smaller the vibration, the louder the sound
④Sound travels well even where there is no air
⑤Sound can happen without any vibration
▸ ① Sound is made when something vibrates
1
Sound is made when something vibrates, and the vibration travels through the air.
2
Faster vibrations make higher sounds (②), bigger vibrations make louder sounds (③), sound cannot travel where there is no air (④), and sound needs vibration to happen (⑤).
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