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Sound waves make the ear drum vibrate; three tiny bones, the hammer, anvil and stirrup, amplify the vibrations and pass them to the cochlea. Free notes.
Sound Waves and Vibrations is part of Waves in air, fluids and solids in GCSE AQA Higher Physics.
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Sound waves make the ear drum vibrate; three tiny bones, the hammer, anvil and stirrup, amplify the vibrations and pass them to the cochlea. Free notes.
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Use this lesson to stay inside Waves in air, fluids and solids while connecting the detail back to the wider Waves topic.
Read the core explanations from Sound Waves and Vibrations before testing yourself from memory.
When you speak, your vocal cords vibrate. When you hear, your ear drum vibrates. This isn't a coincidence — it reveals a fundamental truth about how sound works in our world.
Sound waves don't just travel through air and disappear when they hit solid objects. Instead, they cause those solids to vibrate, and vibrating solids can create new sound waves. This two-way conversion is happening around you constantly, from the speaker in your phone to the walls of your room.
Understanding this connection explains why you can hear through walls, why musical instruments work, and why your hearing has limits. The key insight is that sound and vibration are two forms of the same phenomenon — wave energy moving through different materials.
Picture sound waves as invisible pushes and pulls moving through the air. When these pressure changes reach a solid surface, they don't just bounce off — they transfer their energy to the solid, making it vibrate.
The process works like this: sound waves are regions of high and low pressure moving through air. When a high-pressure region hits a solid surface, it pushes the surface inward slightly. When a low-pressure region follows, it allows the surface to spring back out. This repeated pushing and pulling makes the solid vibrate at the same frequency as the original sound wave.
The ear drum provides the perfect example. Sound waves travelling down your ear canal strike the thin membrane of the ear drum. The alternating high and low pressures cause the ear drum to vibrate back and forth, matching the frequency of the sound. A 440 Hz sound wave makes your ear drum vibrate 440 times per second.
This same principle explains why windows rattle during thunderstorms, why you feel bass frequencies in your chest at concerts, and why stethoscopes work. The sound waves transfer their energy to solid objects, creating vibrations you can see or feel.
The conversion works both ways — vibrating solids can create sound waves in air. When a solid object vibrates, it pushes and pulls on the air molecules next to it, creating the pressure changes we call sound waves.
Consider a guitar string. When you pluck it, the string vibrates back and forth. As it moves in one direction, it compresses the air molecules on that side, creating a high-pressure region. As it swings back, it creates a low-pressure region. These alternating pressure zones travel outward as sound waves.
The frequency of the vibrating solid determines the frequency of the sound wave produced. A guitar string vibrating at 330 Hz creates sound waves with a frequency of 330 Hz. This is why different sized strings produce different pitched notes — thicker strings vibrate more slowly, creating lower frequency sound waves.
Your vocal cords work exactly the same way. Air from your lungs makes your vocal cords vibrate. These vibrations create sound waves in your throat and mouth, which travel out as your voice. The faster your vocal cords vibrate, the higher the pitch of your voice.
Your ear is a masterpiece of wave-to-vibration conversion. Sound waves enter your ear canal and immediately begin a chain of conversions that ends with electrical signals in your brain.
First, sound waves strike your ear drum, causing it to vibrate. The ear drum is connected to three tiny bones called ossicles — the hammer, anvil, and stirrup. These bones amplify the vibrations and pass them to the inner ear. Each bone vibrates in response to the movement of the previous one, maintaining the original frequency throughout.
In the inner ear, the vibrations reach the cochlea, a fluid-filled spiral structure. The vibrating stirrup bone creates pressure waves in the cochlear fluid. These pressure waves cause tiny hair cells to bend, which generates electrical signals sent to your brain. Your brain interprets these signals as sound.
This entire process — from sound wave to ear drum vibration to bone vibration to fluid pressure to electrical signal — happens in milliseconds. The remarkable thing is that the frequency information is preserved at each step, allowing your brain to distinguish between different pitches.
Worked example: Sound Wave to Brain Signal Conversion
Trace how a 1000 Hz sound wave becomes a signal your brain can interpret.
Answer: The 1000 Hz sound wave becomes 1000 Hz electrical pulses sent to the brain, preserving the original frequency information.
The conversion between sound waves and vibrations doesn't work perfectly for all frequencies. Your ear can only detect sounds between about 20 Hz and 20,000 Hz because the physical structures in your ear have limitations.
At very low frequencies (below 20 Hz), your ear drum and the tiny bones can't vibrate effectively. The wavelengths are too long and the pressure changes too gradual for the delicate mechanisms to respond. It's like trying to detect ocean waves with a small cork — the cork just rises and falls gently without much response.
At very high frequencies (above 20,000 Hz), the opposite problem occurs. The ear drum and bones become too stiff to follow the rapid vibrations. The structures can't keep up with the fast pressure changes, so they don't vibrate effectively. Additionally, the hair cells in your cochlea that detect high frequencies are the first to be damaged by age and loud sounds.
This frequency limitation explains why dogs can hear sounds you can't — their ears are built to detect higher frequencies, up to about 45,000 Hz. It also explains why some musical instruments sound different to different people — older listeners may not hear the highest frequency components that younger listeners can detect.
The conversion between sound waves and solid vibrations has countless practical applications. Understanding this principle helps explain how many everyday devices work and why certain phenomena occur.
Stethoscopes work by collecting sound waves from inside your body and converting them to vibrations in the chest piece. These vibrations travel through the solid tubes to your ears, where they're converted back to sound waves. The solid transmission actually improves the sound quality compared to listening through air alone.
Noise-cancelling headphones use this principle in reverse. They detect incoming sound waves, create vibrations in a speaker that produce 'anti-sound' waves, and these cancel out the original noise. The conversion from sound to electrical signal to vibration to anti-sound happens in milliseconds.
Building design must account for sound-vibration conversion. Sound waves can cause walls, floors, and windows to vibrate, transmitting noise between rooms. Architects use materials and designs that either absorb sound waves before they cause vibrations, or prevent vibrations from creating new sound waves on the other side.
Exam questions on this topic often test your understanding of the conversion process and frequency relationships. The key is to remember that frequency is always preserved during conversion — a 500 Hz sound wave creates 500 Hz vibrations, which can create new 500 Hz sound waves.
When describing the ear drum, examiners want you to mention that sound waves cause it to vibrate, and that these vibrations are passed to the bones of the middle ear. Don't just say 'the ear drum detects sound' — explain the physical process of wave-to-vibration conversion.
For questions about hearing limits, remember to link the frequency range to the physical limitations of ear structures. Explain that very low frequencies can't make the ear drum vibrate effectively, and very high frequencies happen too fast for the ear structures to follow.
Common mistakes include thinking that sound waves are 'absorbed' by solids rather than converted to vibrations, or believing that the frequency changes during conversion. Always emphasise that energy is transferred and frequency is preserved.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Noise-cancelling headphones detect incoming sound waves and create vibrations in a speaker that produce 'anti-sound' waves, which cancel out the original noise. This conversion happens in milliseconds.
Sound waves make the ear drum vibrate; three tiny bones, the hammer, anvil and stirrup, amplify the vibrations and pass them to the cochlea. There, pressure waves in the fluid bend tiny hair cells, which generate electrical signals sent to the brain, with the frequency preserved at each step.
A stethoscope collects sound waves from inside the body and converts them to vibrations in the chest piece. These vibrations travel through the tubes to the listener's ears, where they are converted back to sound waves.
Dogs can hear up to about 45,000 Hz because their ears are built to detect higher frequencies. Humans can only hear between about 20 Hz and 20,000 Hz.
Sound waves are regions of high and low pressure; when they reach the ear drum, high pressure pushes it inward and low pressure lets it spring back. This makes the ear drum vibrate at the same frequency as the sound, so a 440 Hz sound makes it vibrate 440 times per second.
Air from the lungs makes the vocal cords vibrate, and these vibrations create sound waves in the throat and mouth that travel out as the voice. The faster the vocal cords vibrate, the higher the pitch.
A vibrating object pushes and pulls on the air next to it, creating alternating high and low pressure regions that travel outward as sound waves. A guitar string vibrating at 330 Hz creates sound waves with a frequency of 330 Hz.
Frequency is always preserved when sound waves are converted to vibrations in solids: a 500 Hz sound wave creates 500 Hz vibrations, which can create new 500 Hz sound waves. Energy is transferred, but the frequency stays the same.
Humans cannot hear frequencies under about 20 Hz because the ear drum and the tiny bones cannot vibrate effectively at such low frequencies. The wavelengths are too long and the pressure changes too gradual for the delicate mechanisms to respond.
Humans cannot hear frequencies over about 20,000 Hz because the ear drum and bones are too stiff to follow such rapid vibrations. The hair cells that detect high frequencies are also the first to be damaged by age and loud sounds.
The ossicles are three tiny bones in the ear, the hammer, anvil and stirrup, connected to the ear drum. They amplify the ear drum's vibrations and pass them to the inner ear, keeping the original frequency.
The cochlea is a fluid-filled spiral structure in the inner ear. The vibrating stirrup bone creates pressure waves in its fluid, which bend tiny hair cells that generate electrical signals sent to the brain.
Windows rattle in thunderstorms because the sound waves transfer their energy to the solid glass and make it vibrate. The same effect explains feeling bass frequencies in the chest at concerts.
Sound can be heard through walls because sound waves make the wall vibrate, and the vibrating wall creates new sound waves on the other side. Architects use materials that absorb sound waves or stop vibrations creating new sound waves.