Sound Waves
In 1992, Australian researchers measured whale song at 188 dB, louder than a jet engine, travelling 3,000 km through the ocean.
At the start of this lesson you were shown sound travelling nearly 17 times faster through steel than air, and how Indigenous Australians pressed their ears to the ground to detect distant vibrations long before European contact.
Now that you've worked through the lesson, how has your thinking shifted? Can you explain that hook idea more precisely using what you've learned today?
Answers
▾MCQ 1
BPitch is determined by frequency. Higher frequency means higher pitch; lower frequency means lower pitch.
MCQ 2
AIn solids like steel, particles are close together and tightly bonded, so vibrations transfer from particle to particle very quickly. In gases like air, particles are far apart, so vibrations take longer to transfer.
MCQ 3
CThe didgeridoo produces a sustained low note because its long tube creates a low-frequency standing wave. A clapstick produces a brief, sharp percussive sound with a broad range of frequencies, including higher-frequency components.
MCQ 4
DThe Moon has virtually no atmosphere, so there is no medium for sound to travel through. The astronaut sees the flash because light is an electromagnetic wave that does not need a medium.
MCQ 5
BThe speed of sound in air depends on the temperature and properties of the air, not on the amplitude of the sound. Shouting louder increases the amplitude (making the echo louder) but does not change the speed or the time it takes to return.
Short Answer 1
Model answer: Sound is a longitudinal mechanical wave because the particles of the medium oscillate parallel to the direction the wave travels. As sound travels through air, vibrating objects push air particles together to form compressions (high pressure) and then let them spring back to form rarefactions (low pressure). These compressions and rarefactions travel outward from the source. Sound cannot travel through a vacuum because it is a mechanical wave that requires a medium. In a vacuum there are no particles to compress and rarefy, so no sound wave can form or propagate.
Short Answer 2
Model answer: For the first singer, singing high then low notes at the same volume: the frequency changes (high note = high frequency, low note = low frequency), which means the pitch changes. The amplitude stays the same, so the volume stays the same. For the second singer singing the same notes much more quietly: the frequency still changes between high and low notes (so pitch still changes), but the amplitude is lower for both notes, meaning the volume is quieter for both. In summary, the first singer changes pitch only; the second singer changes both pitch and volume.
Short Answer 3
Model answer: The didgeridoo produces sound when the player vibrates their lips at the mouthpiece, setting up a standing wave inside the hollow tube. The air column inside vibrates with compressions and rarefactions travelling along its length. The length of the didgeridoo affects its pitch because a longer tube supports a longer wavelength standing wave, which corresponds to a lower frequency and therefore a lower pitch. This demonstrates understanding that sound is a longitudinal wave whose properties (frequency, wavelength, pitch) depend on the dimensions of the resonating chamber, the same principles that govern all wind instruments in Western and non-Western music traditions.
Wave Jumper
Jump through the sound wave platforms while testing your knowledge of pitch, volume and the speed of sound. Can you hear your way to the top?
Model answers (click to reveal)
Answers
▾MCQ 1
BPitch is determined by frequency. Higher frequency means higher pitch; lower frequency means lower pitch.
MCQ 2
AIn solids like steel, particles are close together and tightly bonded, so vibrations transfer from particle to particle very quickly. In gases like air, particles are far apart, so vibrations take longer to transfer.
MCQ 3
CThe didgeridoo produces a sustained low note because its long tube creates a low-frequency standing wave. A clapstick produces a brief, sharp percussive sound with a broad range of frequencies, including higher-frequency components.
MCQ 4
DThe Moon has virtually no atmosphere, so there is no medium for sound to travel through. The astronaut sees the flash because light is an electromagnetic wave that does not need a medium.
MCQ 5
BThe speed of sound in air depends on the temperature and properties of the air, not on the amplitude of the sound. Shouting louder increases the amplitude (making the echo louder) but does not change the speed or the time it takes to return.
Short Answer 1
Model answer: Sound is a longitudinal mechanical wave because the particles of the medium oscillate parallel to the direction the wave travels. As sound travels through air, vibrating objects push air particles together to form compressions (high pressure) and then let them spring back to form rarefactions (low pressure). These compressions and rarefactions travel outward from the source. Sound cannot travel through a vacuum because it is a mechanical wave that requires a medium. In a vacuum there are no particles to compress and rarefy, so no sound wave can form or propagate.
Short Answer 2
Model answer: For the first singer, singing high then low notes at the same volume: the frequency changes (high note = high frequency, low note = low frequency), which means the pitch changes. The amplitude stays the same, so the volume stays the same. For the second singer singing the same notes much more quietly: the frequency still changes between high and low notes (so pitch still changes), but the amplitude is lower for both notes, meaning the volume is quieter for both. In summary, the first singer changes pitch only; the second singer changes both pitch and volume.
Short Answer 3
Model answer: The didgeridoo produces sound when the player vibrates their lips at the mouthpiece, setting up a standing wave inside the hollow tube. The air column inside vibrates with compressions and rarefactions travelling along its length. The length of the didgeridoo affects its pitch because a longer tube supports a longer wavelength standing wave, which corresponds to a lower frequency and therefore a lower pitch. This demonstrates understanding that sound is a longitudinal wave whose properties (frequency, wavelength, pitch) depend on the dimensions of the resonating chamber, the same principles that govern all wind instruments in Western and non-Western music traditions.