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Sound, vibrations and wave descriptions - Science Year 7

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Introduction

How can a sound travel across a room while the air does not stream from the speaker to your ear? Connect vibration, a material medium and a receiver, then separate pitch from loudness using clearly labelled records.

Read original pressure-time sample models, calculate simple frequencies and echoes, and evaluate a supplied sound-insulation comparison. All numerical records are fictional. You do not need to make loud sounds, wear headphones, access a microphone, evacuate a jar or carry out an experiment. Year 7 is an editorial placement within England’s shared KS3 programme.

Connect source, medium and longitudinal vibration

A source vibrates and disturbs a medium. A vibrating drum skin, loudspeaker cone or tuning-fork prong can disturb surrounding air. Local changes of pressure and density spread through interactions in the medium. At another location, pressure variations can make a receiver such as an eardrum or microphone diaphragm vibrate. Identify source, medium and receiver separately: a vibrating source alone does not guarantee that a particular listener receives an audible sound.

In air, the elementary sound model is longitudinal. The local back-and-forth motion associated with the disturbance is parallel to the direction in which it propagates. A compression is a region with greater pressure/density than the local undisturbed air; a rarefaction has lower pressure/density. These regions travel, while individual particles have small oscillatory motion superimposed on their random molecular motion. Air molecules do not generally travel the whole source-to-ear distance as the sound signal.

Use a tracked-particle model within its limits. In this original strip, x marks the same model particle at five equally spaced instants of one cycle. The horizontal direction is parallel to propagation. Dots are position guides, not other particles. The middle position is equilibrium: the particle moves right, returns through the middle, moves left and returns again.

start       ..x..
quarter     ...x.
half        ..x..
threequarter .x...
full        ..x..

The particle’s local back-and-forth movement is distinct from a travelling compression pattern. This strip does not represent the whole wave, random molecular motion or actual particle scale. A one-dimensional row is not a claim that real air molecules stay fixed in a neat line. A spring can also model compressions, but its coils are not actual air molecules and a hand-driven demonstration is not required here.

A drawn sine curve of pressure against time is a graph of a changing quantity at a location. It is not the literal up-and-down route of a sound particle through the room. Likewise, a diagram of displacement against distance is a different graph from pressure against time. Always check the axes and represented quantity before assigning amplitude, period or wavelength. The shape alone is not a description of direction of particle travel.

Sound needs a material pathway. Sound can travel through gases, liquids and solids; speeds depend on the medium and its conditions. There is no single universal 'sound speed' applying to every substance and temperature. Sound cannot cross a perfect vacuum as an ordinary mechanical wave because the medium needed for transmission is absent. Electromagnetic waves such as visible light can cross a vacuum and therefore do not obey this same requirement.

In a described bell-jar demonstration, a bell may continue to vibrate while removing air reduces the airborne sound reaching a listener. That supports the role of the medium. A real apparatus can still transmit some vibration through solid supports, and residual gas or background sound can remain, so it is inaccurate to promise that every partly evacuated setup becomes perfectly silent. No jar, pump, electricity or pressure vessel is operated in this course.

Think of a fictional signal chain: source vibration → pressure disturbance in air → receiver vibration → interpreted signal. A weak source, absent medium, blocked pathway, unsuitable receiver or frequency outside a listener’s range can make the signal inaudible for different reasons. 'No one heard it' is not by itself proof that the source did not vibrate.

Compare pressure traces, frequency and amplitude

Count complete cycles in a stated time. Frequency is the number of complete oscillations per second, measured in hertz, Hz. A higher frequency generally corresponds to a higher pitch for comparable simple audible tones. Pitch is a perception, whereas frequency is a physical quantity. Complex sounds can contain several frequency components, so one neat sine wave is a useful starting model rather than a complete account of every musical or spoken sound.

$f = \frac{N}{t}$

Here N counts complete cycles and t is the corresponding elapsed time in seconds. Do not count both a compression and the following rarefaction as two full cycles. If the time axis is in milliseconds, divide its numerical value by 1000 to express seconds. A cycle lasting 20 ms takes 0.020 s; one cycle in that time gives 50 Hz. A 10 ms period gives 100 Hz, twice the frequency.

Three original pressure-time models. Each table lists five sample points within one ideal repeating sinusoidal cycle. The pressure values are relative changes about equilibrium, in arbitrary relative units. Connect them with a smooth periodic curve for the supplied model; the numbers are not measured sound pressure, an oscilloscope photograph or a decibel scale. The repeating-cycle assumption is supplied, not proved by five isolated measurements.

Trace A

Time/ms	Relative pressure change
0	0
5	1
10	0
15	-1
20	0

Trace B

Time/ms	Relative pressure change
0	0
2.5	1
5	0
7.5	-1
10	0

Trace C

Time/ms	Relative pressure change
0	0
5	2
10	0
15	-2
20	0

A has a 20 ms period and relative pressure amplitude 1. B has a 10 ms period with the same relative amplitude 1. B therefore represents a higher-frequency simple tone: 100 Hz compared with 50 Hz. C has the same 20 ms period as A but amplitude 2, so it retains the 50 Hz frequency while representing a larger pressure variation. Its greater amplitude does not automatically make its pitch higher.

Define amplitude carefully. Amplitude is the maximum change from the equilibrium value, not the complete positive-to-negative span. Trace C reaches +2 and −2 relative units: amplitude is 2 and peak-to-peak span is 4. A reaches +1 and −1: amplitude 1 and span 2. For otherwise comparable sounds reaching the same listener, greater pressure amplitude usually gives a louder perception, but loudness also depends on frequency, hearing, duration and context.

A decibel sound-level reading is logarithmic and referenced; it is not identical to an arbitrary trace amplitude. Doubling the height of C’s drawn pressure trace does not mean doubling its decibel number, and 'twice as loud' is not a universal arithmetic rule from these relative units. You do not need decibel calculations or to play the model at any volume.

In a separate counting record, P contains four cycles in 0.02 s, Q eight in 0.02 s and R four in 0.02 s. Their frequencies are 200, 400 and 200 Hz. These are different records from A/B/C’s single-cycle tables. Compare cycles per second rather than merely the number visible on screens that may cover different time windows.

Counting record	Complete cycles	Time/s	Frequency/Hz
P	4	0.02	200
Q	8	0.02	400
R	4	0.02	200

Explain distance, echoes and sound absorption

A sound can become fainter without changing pitch. For a source radiating into a large open space, the transferred energy spreads over larger areas as distance increases. Absorption by the medium and obstacles can also reduce a received signal. A greater distance does not require the source to oscillate less often each second. For a stationary source and listener in a steady medium, frequency generally stays the same while amplitude can decrease. Relative motion can shift received frequency, but that is a separate effect rather than the reason every distant sound is quieter.

Room reflections, barriers and source direction can make real patterns complicated. Do not infer that every additional metre produces the same reduction or that an arbitrary classroom follows an exact simple distance rule. The elementary explanation is energy spreading/transfer with specified limits, not energy being destroyed. An ear or microphone records the signal at its location, not every joule emitted by the source.

Reflection gives an echo with a travel-time delay. A sufficiently distinct reflected sound can be heard or recorded later than the direct signal. In a fictional straight out-and-back model, sound speed is supplied as 340 m/s and the elapsed time from emission to returning echo is 0.60 s. The sound travels 340 × 0.60 = 204 m in total. If source and receiver are together and the reflecting wall is directly along that path, its distance is half: 102 m.

$d_{w a l l} = \frac{v t_{e c h o}}{2}$

The factor of two is for the outward and return trips, not an arbitrary correction for echoes. For a second model with the same supplied speed and a 0.20 s echo delay, total path is 68 m and wall distance is 34 m. If the receiver is elsewhere or the path is not the stated straight out-and-back route, this simple expression cannot be applied unchanged. The supplied 340 m/s is an approximation for that model, not a universal value for all air conditions.

Absorption, reflection and transmission differ. A surface may reflect some incident sound, transmit some and absorb some. Absorbed sound energy becomes dispersed, often increasing internal energy, rather than vanishing from the complete account. Soft or porous treatments can reduce some reflections; a sound barrier aims to reduce transmission to another location. Absorbing echoes inside a room and preventing sound reaching the next room are related but different design tasks.

Thin materials, gaps, structure-borne paths, thickness and frequency all affect performance. A claim that any soft-looking surface blocks every sound is unsupported. A camera photograph of foam cannot establish a measured sound reduction, and this lesson’s paper models are not permission to install materials or certified hearing protection. Keep pathways and the intended receiver clear before recommending an arrangement.

Evaluate sound-insulation evidence and model limits

Evaluate a controlled comparison. An invented test keeps the same source setting, simple-tone frequency, source/receiver positions, room conditions, panel area and microphone gain. It compares a no-barrier arrangement with panels B and C. The recorded numbers below are relative microphone signal amplitudes, not decibels or human loudness ratings. No microphone access or physical test is requested.

Fictional arrangement	Trial 1 relative signal	Trial 2 relative signal	Trial 3 relative signal
No barrier	10.0	10.2	9.8
Panel B	6.0	6.2	5.8
Panel C	3.0	3.2	2.8

Mean received signals are 10.0 without a barrier, 6.0 for B and 3.0 for C. Each three-trial range is 0.4 relative units. For this frequency and arrangement, C gives the smallest received signal. Its mean is 30% of the no-barrier value: a 70% reduction in this recorded amplitude measure. Do not call that 70% less energy, 70% lower decibels or a universal 70% reduction in perceived loudness.

The results support C under the supplied conditions, not an absolute ranking of every use or frequency. If C were placed farther from the microphone, used a larger panel, changed source volume or changed microphone gain, the comparison could be confounded. Repeats show variation but do not correct a systematically miscalibrated sensor. A professional report would also describe equipment, uncertainties, source direction, reflected paths and the frequency range of interest.

Use hearing examples inclusively. Roughly 20 Hz to 20,000 Hz is a commonly quoted young-human audible range, not a guarantee that every listener hears every signal in it. Age, hearing differences, sound level and background conditions matter. A sound outside one listener’s hearing may still be a real pressure wave or be detected by a different receiver. No frequency sweep, loudness challenge or headphone test is needed to complete any task.

Use the original FuseSchool visual examples to identify a vibrating source, transmission through a medium and a receiver. Compare the animation with the written pressure-time models. Demonstrations in the video are observations to interpret, not instructions to build apparatus, use a flame, evacuate glass or raise volume. Original: FuseSchool - Global Education, Sound Wave Experiments | Waves | Physics | FuseSchool. The written explanations and native tasks work without sound or the external player.

Correct three tempting shortcuts. A larger pressure amplitude is not automatically a higher frequency. A sine-shaped pressure graph is not the literal route of an air molecule. A faint received sound does not prove its source stopped oscillating. Explain each correction using A/B/C, the tracked-particle strip or a specific signal pathway, rather than merely labelling the statement wrong.

Build a sound portfolio: a source–medium–receiver explanation, labelled compression/rarefaction model, three original waveform sketches, all cycle/echo calculations and a qualified B/C recommendation. State the axes, units, equilibrium, amplitude and time window. Identify at least one particle-model limitation and one measurement limitation. This records conceptual explanation and supplied-data reasoning, not laboratory performance, audiometry or installation competence.

Interactive Tasks

Quiz: Test Your Knowledge

Which statement best describes ordinary sound transmission through air? (A pressure disturbance propagates while particles have local oscillatory motion) (!Every molecule travels from the speaker to the listener) (!Sound needs no material medium) (!Air particles trace a giant sine-shaped route across the room)

What distinguishes longitudinal motion in the elementary sound model? (Local vibration is parallel to propagation) (!Local vibration must be perpendicular to propagation) (!There is no vibration) (!Only light can use the model)

Why does reducing air in a bell-jar description reduce airborne sound? (It reduces the medium available to transmit the disturbance) (!It necessarily stops the bell vibrating) (!It makes all solid supports unable to vibrate) (!It converts sound directly into visible light)

A simple tone completes one cycle in 20 ms. What is its frequency? (50 Hz) (!20 Hz) (!0.02 Hz) (!20000 Hz)

How do the original trace B and trace A compare? (B has twice the frequency and the same relative pressure amplitude) (!B has the same frequency and twice the amplitude) (!B has half the frequency) (!B has four times the pressure amplitude)

Trace C reaches +2 and −2 relative pressure units. What is its amplitude? (2 relative units) (!4 relative units) (!Zero relative units) (!50 relative units)

What does eight complete cycles in 0.02 s represent? (400 Hz) (!160 Hz) (!0.16 Hz) (!40 Hz)

A model echo returns in 0.60 s at supplied 340 m/s. How far is the wall under the stated out-and-back assumptions? (102 m) (!204 m) (!566.7 m) (!34 m)

What do the barrier records directly support? (C gives the smallest mean recorded amplitude under the stated conditions) (!C removes all sound at every frequency) (!The values are calibrated decibels) (!A 70 percent amplitude reduction proves 70 percent less perceived loudness)

Why may sound become fainter as distance increases from a stationary source? (Energy spreads and can be absorbed while frequency need not change) (!Frequency must decrease by one hertz per metre) (!All particles stop vibrating immediately) (!Every room has identical reflection and absorption)

Memory Game

Compression	A region of increased pressure and density in the elementary air model
Rarefaction	A region of reduced pressure and density in that model
Frequency	Complete oscillations per second
Amplitude	Maximum change from the equilibrium value
Medium	Material through which a mechanical disturbance propagates
Echo	A delayed reflected sound

Drag and Drop

Larger pressure amplitude at unchanged period	A stronger pressure variation without a higher frequency
Shorter repeating period	A greater number of cycles per second
Absent material in a perfect vacuum	No ordinary mechanical sound pathway across the gap
Source and receiver beside the same reflecting path	Echo timing includes outward and return travel
Changing gain during a barrier comparison	A confounded received-signal comparison

Crossword Puzzle

VIBRATION	What repeated motion can produce sound?
MEDIUM	What material carries a mechanical sound disturbance?
FREQUENCY	What quantity counts complete cycles per second?
AMPLITUDE	What quantity measures the maximum variation from equilibrium?
COMPRESSION	What region has greater air pressure and density in the model?
ECHO	What delayed reflected sound can reveal a travel-time interval?

LearningApps

Optional extra practice. Choose an appropriate activity with your teacher. If the external collection is unavailable, use the native activities and independent tasks in this course.

Cloze Text

Open Tasks

Easy

Explain the sound chain: Describe a vibrating source, air disturbance and receiver; distinguish a travelling compression from a particle’s local motion.
Label a longitudinal model: Label compression, rarefaction, equilibrium, particle vibration and propagation direction using the original tracked-particle strip and the written explanation.
Calculate simple frequencies: Convert the A/B periods from milliseconds to seconds and calculate both frequencies; interpret the separate P/Q/R counting records.
Distinguish pitch and loudness: Compare A/B/C’s periods, amplitudes and peak-to-peak spans without equating amplitude to decibels.

Standard

Draw pressure-time models: Sketch the three supplied cycles using labelled axes, a stated smooth repeating assumption and correct different time windows.
Explain the bell-jar evidence: Explain why reduced airborne sound supports the medium model while retained supports/residual gas limit a perfect-silence claim.
Calculate two echoes: Find both total path lengths and wall distances, explaining the factor of two and supplied sound-speed assumption.
Analyse barrier records: Calculate all means/ranges and C’s relative amplitude reduction, then state precisely which quantities were not measured.

Advanced

Evaluate a soundproofing claim: Distinguish absorption, reflection and transmission and explain why an echo treatment does not guarantee full isolation of the next room.
Design a fair paper comparison: Specify source, frequency, distances, panel geometry, room and microphone controls for a fictional comparison, without actually producing loud sounds.
Critique an unreliable waveform inference: Explain why shape without axis labels or cycle counts without a time window cannot establish pitch, amplitude or particle direction.
Present a sound evidence portfolio: Combine the mechanism, original trace sketches, frequency/echo arithmetic and qualified barrier conclusion with particle-model, hearing and measurement limits.

Learning Check

Source and medium: Explain a travelling sound disturbance without source-to-ear particle transport.
Vacuum and hearing evidence: Interpret the bell-jar description with limits.
Trace and cycle calculations: Compare all three original traces and the counting records.
Echo paths: Solve both distances with the appropriate boundary conditions.
Received amplitude comparison: Calculate the barrier evidence and qualify the recommendation.
Distance and absorption: Explain a fainter signal and distinguish room treatments.

Worked checks and assessment guidance

A vibrating source disturbs surrounding material, and local interactions propagate pressure/density variations to a receiver. In the elementary air model, vibration is parallel to propagation; compression/rarefaction regions progress while particles oscillate locally in addition to random motion. The tracked-particle strip is a one-dimensional model, not a molecular film or the whole compression pattern. A pressure-time sine curve shows a varying quantity, not an up-and-down path followed by the air from speaker to ear.
Sound needs a medium and cannot cross a perfect vacuum as an ordinary mechanical wave. Removing air can reduce airborne transmission even while the bell continues vibrating. Residual gas, supports and background sound mean a real partial evacuation need not be completely silent. Light can cross a vacuum. Inaudibility for one person may also reflect source strength, reception, frequency range or surroundings, so it does not alone prove no vibration. No pressure apparatus or hearing test is performed.
A’s 20 ms period is 0.020 s, giving 50 Hz and amplitude 1. B’s 10 ms is 0.010 s, giving 100 Hz with amplitude 1. C keeps 20 ms/50 Hz but has amplitude 2 and peak-to-peak span 4. Thus B is higher frequency than A, while C has a larger pressure variation without a higher frequency. The separate P/Q/R counts give 4/0.02 = 200 Hz, 8/0.02 = 400 Hz, 4/0.02 = 200 Hz. Arbitrary amplitude units are not decibels or a calibrated loudness scale.
For 340 m/s and 0.60 s, total sound path is 204 m; with source/receiver together and a straight outward/return reflection, wall distance is 102 m. For 0.20 s, total path is 68 m and wall distance 34 m. Divide by two for the two legs, not because every sound problem needs halving. Changed receiver position/path or a different medium requires another model; 340 m/s is a supplied approximation, not a universal constant.
No-barrier mean is10.0; B is6.0; C is3.0 relative units. All ranges are0.4. C gives30% of baseline and a70% decrease in the recorded amplitude measure under fixed source, frequency, positions, room, geometry and gain. This is not a measured70% decrease in energy, decibels or perceived loudness, nor a guarantee at every frequency. Repeats do not remove systematic bias, and changed geometry/gain can confound the comparison.
Energy spreading, absorption and obstacles can reduce amplitude at a receiver without reducing the frequency of a stationary source in a steady medium. Real reflections/direction complicate a simple distance rule; relative-motion frequency shifts are a separate effect. Reflection redirects sound, transmission carries it through a barrier and absorption transfers it into other accounts such as internal energy. Echo reduction within a room is not identical to isolating the next room, and absorbed energy is not destroyed.

Learning evidence

Keep the source/medium/receiver explanation, a labelled longitudinal model, three correctly scaled original pressure-time sketches, independent period/frequency/amplitude/span calculations, both echo paths and a qualified barrier analysis. State graph, hearing, measurement and particle-model limits. No loud exposure, audiometry, microphone recording, pressure-vessel operation or physical practical is claimed.

OER and Wikipedia

Original teaching, tracked-particle strip, A/B/C pressure-time models, separate P/Q/R cycle records, echo calculations, invented relative-amplitude barrier trials, activities and worked feedback. The actual Commons states-of-matter schematic remains unchanged with its source/creator/licence record. It illustrates potential media, not a wave or universal molecular composition. Two additional researched Commons wave animations were unavailable to the native parser; they are not embedded or counted as functioning media. Their concepts are taught through the original strip, trace models and actual embedded video. The original FuseSchool video was checked for title, publisher, playability, embedding and preview; the full film was not watched and no transcript/timestamp claim is asserted. Demonstrations are not practical instructions. No protected worksheet or extended source wording is copied.

Department for Education: KS3 Science, Sound waves, with editorial Year7 placement. NASA Science: Anatomy of an Electromagnetic Wave, consulted for the mechanical/electromagnetic medium distinction and model limitations. National Park Service: Understanding Sound, consulted for frequency/amplitude and reception. Its shorthand equating physical frequency with perceived pitch, amplitude with a decibel measure, or a universal doubling of perceived loudness is not adopted. No US workplace rule is presented as UK guidance. Reviewed 13 November 2026.

Solid liquid gas.svg, Luis Javier Rodriguez Lopez (Yupi666); SVG conversion: Tomtheman5, CC BY 2.5. Unchanged original; caption and learning activities are original.