Sound
Sound
Sound-Vibrations, Waves and the Science of Hearing
Close your eyes for a moment and just listen. You may hear a fan whirring, a bird calling outside, a friend talking, or traffic in the distance. Every one of those sounds began the same way — with something vibrating. Sound is one of the most familiar things in our daily life, yet the physics behind it is beautifully simple and surprisingly deep.
In this chapter we will discover how sound is produced, how it travels, how our ears catch it, what makes one sound loud and another shrill, and why too much sound becomes a serious pollution problem.
1 | How Is Sound Produced?
Sound is produced by vibrating objects. A vibration is a rapid to-and-fro motion of an object about its rest position. When an object vibrates, it pushes the air particles around it back and forth, and this disturbance travels outward as sound.
FOUNDATIONAL CONCEPT
No vibration means no sound. Every single sound you have ever heard — a drumbeat, a whisper, a scream, a violin — was created by something vibrating. Stop the vibration and the sound stops instantly.
A VIBRATING RULER ON A TABLE EDGE
Press the free end of a ruler and release it. It moves up and down repeatedly about its rest position — that is a vibration — and you hear a buzzing sound. Hold the ruler tightly and the sound dies at once.
Vibrations You Can Actually See and Feel
| Object | What Vibrates | How to Notice It |
|---|---|---|
| Drum / Tabla | Stretched membrane | Sprinkle grains on it — they jump about |
| Guitar / Sitar | Stretched string | The plucked string looks blurred |
| School Bell | Metal body | Touch it — you feel a tingling; sound stops |
| Flute / Whistle | Air column inside | Closing holes changes the note |
| Your Throat | Vocal cords | Touch your throat and hum — you feel it buzz |
2 | Sound Produced by Humans
In human beings, sound is produced by the voice box or larynx. It lies at the upper end of the windpipe. If you place your hand on your throat and hum, you can feel a small bump vibrating — that is your larynx at work. This bump is often called the Adam’s apple.
Two stretched bands of muscle called the vocal cords are fixed across the voice box, leaving a narrow slit between them. When we speak, air from the lungs is forced up through this slit. The rushing air makes the vocal cords vibrate — and those vibrations become our voice.
HOW THE VOCAL CORDS MAKE DIFFERENT VOICES
MEN
Cords about 20 mm long
Thick & long → Deep voice
WOMEN
Cords about 15 mm long
Shorter → Higher voice
CHILDREN
Cords about 5–6 mm long
Very short → Shrill voice
The rule: shorter and thinner vocal cords vibrate faster, and faster vibration gives a higher, shriller voice.
DID YOU KNOW?
Boys’ voices “break” and become deeper during adolescence because the larynx grows larger and the vocal cords become longer and thicker. Birds do not have a larynx at all — they sing using a special organ called the syrinx, located deeper down where the windpipe splits.
3 | Sound Needs a Medium to Travel
A vibrating object cannot send sound to your ear all by itself. It needs a medium — a material made of particles that can be pushed and pulled. The vibrating object nudges the particles next to it, those particles nudge their neighbours, and the disturbance is handed along like a message passed down a line of people.
Very importantly, the particles themselves do not travel from the source to your ear. Each particle only wobbles about its own position and passes the energy forward. It is the disturbance that travels, not the matter.
CRITICAL RULE — REMEMBER THIS
Sound cannot travel through a vacuum. A vacuum has no particles, so there is nothing to carry the disturbance. This is why outer space is completely silent — astronauts standing side by side on the Moon must use radios to talk, even though they are only a metre apart.
HOW FAST DOES SOUND TRAVEL?
STEEL (Solid) — particles packed very tightly
≈ 5,100 m/s — fastest
WATER (Liquid) — particles fairly close
≈ 1,500 m/s — medium
AIR (Gas) — particles far apart
≈ 344 m/s — slowest of the three
VACUUM — no particles at all
0 m/s — NO SOUND
The pattern: the closer the particles, the faster they can pass the disturbance along. So sound travels fastest in solids, slower in liquids, and slowest in gases — exactly the opposite of light!
Everyday Proof That Sound Needs a Medium
Through Solids
Press your ear to a table and gently scratch the far end with a fingernail. The scratching is surprisingly loud — the wooden table carries sound better than air does.
Through Liquids
Clap two stones together under water while your head is submerged — you hear it clearly. Whales and dolphins use this to communicate across many kilometres of ocean.
Through Gases
This is how you hear almost everything — voices, music, traffic. Air is the medium we use most, even though it is the poorest carrier of the three.
Through Vacuum — Never
Put a ringing alarm inside a jar and pump the air out. As the air thins, the ringing fades away — even though you can still see the hammer striking.
4 | How We Hear — The Human Ear
The ear is a remarkable instrument that catches vibrations from the air and converts them into signals your brain can understand. It has three parts: the outer ear, the middle ear and the inner ear.
THE JOURNEY OF A SOUND INTO YOUR BRAIN
STEP 1 · PINNA (outer ear flap)
The funnel-shaped flap you can see and touch. It collects sound from the surroundings and directs it inward.
▼
STEP 2 · EAR CANAL
A short tube that carries the sound inward to the eardrum.
▼
STEP 3 · EARDRUM (tympanic membrane)
A thin, tightly stretched membrane — like the skin of a tiny drum. Arriving sound pushes and pulls it, making it vibrate. This is the heart of hearing.
▼
STEP 4 · MIDDLE EAR — three tiny bones
The hammer, anvil and stirrup — the smallest bones in your whole body. They amplify the vibrations and pass them to the inner ear.
▼
STEP 5 · INNER EAR — the cochlea
A spiral, fluid-filled chamber. Here vibrations are converted into electrical signals.
▼
STEP 6 · AUDITORY NERVE → BRAIN
The nerve carries the signals to the brain, which interprets them — and only now do you actually “hear” the sound.
SAFETY WARNING
Never poke anything into your ear. The eardrum is extremely thin and delicate. A pin, pencil, hairpin or cotton bud pushed too far can tear it and cause permanent hearing loss. Ear wax is normal and protective — the ear cleans itself.
5 | Amplitude, Time Period and Frequency
To describe a vibration precisely, scientists use three quantities. Understanding these three unlocks everything else in this chapter.
AMPLITUDE
The maximum distance the object moves away from its rest position.
Decides: LOUDNESS
TIME PERIOD
The time taken for one complete to-and-fro vibration. Measured in seconds.
Symbol: T · Unit: second
FREQUENCY
The number of vibrations in one second.
Decides: PITCH · Unit: hertz (Hz)
THE KEY RELATIONSHIP
Frequency = 1 ÷ Time Period
Frequency and time period are reciprocals of each other. If a pendulum takes 0.5 s for one swing, its frequency is 1 ÷ 0.5 = 2 Hz. One hertz means one vibration per second. A frequency of 500 Hz means the object vibrates 500 times every second.
6 | Loudness and Pitch
Students very often mix these two up, so read this section slowly. Loudness and pitch are completely different properties, controlled by completely different things.
LOUDNESS ← DEPENDS ON AMPLITUDE
SOFT SOUND — Small Amplitude
Gentle tap on a drum
Less energy → soft sound
LOUD SOUND — Large Amplitude
Hard strike on the same drum
More energy → loud sound
Loudness is proportional to the square of the amplitude. Double the amplitude and the sound becomes four times louder. Loudness is measured in decibels (dB).
PITCH ← DEPENDS ON FREQUENCY
LOW PITCH — Low Frequency
Few vibrations per second — waves spread out
Drum, lion’s roar, man’s voice
HIGH PITCH — High Frequency
Many vibrations per second — waves crowded
Whistle, bird chirp, child’s voice
Pitch is also called shrillness. Higher frequency = higher pitch = shriller sound.
Loudness vs Pitch — The Difference at a Glance
| Point of Difference | LOUDNESS | PITCH |
|---|---|---|
| Depends on | Amplitude of vibration | Frequency of vibration |
| Tells us | How strong or faint the sound is | How shrill or deep the sound is |
| Unit | Decibel (dB) | Hertz (Hz) — from frequency |
| Example — high | A loud drumbeat, a shout | A whistle, a mosquito’s buzz |
| Example — low | A whisper, rustling leaves | A drum, a lion’s roar |
| Can they vary alone? | Yes — a whistle can be soft (low loudness) yet still shrill (high pitch). A drum can be loud yet still deep. | |
7 | Audible and Inaudible Sounds
Human ears cannot hear every frequency. There is a definite window of frequencies we can detect — this is called the audible range. Sounds outside it are perfectly real, but our ears simply cannot pick them up.
THE FREQUENCY SPECTRUM
INFRASONIC
Below 20 Hz
AUDIBLE RANGE
20 Hz — 20,000 Hz
ULTRASONIC
Above 20,000 Hz
Who Hears Infrasound?
Elephants, whales, rhinoceroses. Some animals sense the infrasound produced before an earthquake or storm, which is why they behave strangely just before a disaster.
The Human Window
Young children can hear up to about 20,000 Hz. As we grow older this upper limit falls — many adults over 60 cannot hear beyond 15,000 Hz.
Who Hears Ultrasound?
Dogs, bats, dolphins, rats, porpoises. Dog whistles work on this principle — the dog comes running while humans hear nothing at all.
USEFUL APPLICATIONS
Bats fly in total darkness by producing high-pitched squeaks and listening for the echoes that bounce back — this is called echolocation. Doctors use the same idea in ultrasound scans to see inside the body, and ships use SONAR to map the sea floor.
8 | Noise, Music and Noise Pollution
Not all sound is pleasant. Sounds that are pleasing to the ear are called music; sounds that are unpleasant are called noise. The difference is not just about volume — a soft dripping tap at 2 a.m. is noise, while a loud orchestra is music.
MUSIC
Produced by regular and periodic vibrations. Pleasing to the ear. Examples: a sitar, a flute, singing, a tabla being played rhythmically.
NOISE
Produced by irregular and non-periodic vibrations. Unpleasant and jarring. Examples: horns, machinery, construction drilling, shouting.
AN IMPORTANT SUBTLETY
Music can become noise if it is too loud or heard at the wrong time. Loud music near your ear damages your hearing exactly as much as machinery does — the eardrum does not care whether the sound was pleasant.
What Is Noise Pollution?
The presence of excessive or unwanted sound in the environment is called noise pollution. It is invisible, leaves no residue behind — and is therefore very easy to ignore, which is exactly what makes it dangerous.
THE DECIBEL SCALE — HOW LOUD IS TOO LOUD?
Rustling leaves · 10 dB
Normal conversation · 60 dB
Safe limit for continuous exposure · 80 dB
Heavy traffic / loud horn · 90 dB
Firecracker / rock concert · 120 dB
Jet engine at close range · 140 dB
Sounds above 80 dB become physically painful and damaging with prolonged exposure.
Causes, Harms and Solutions
| CAUSES of Noise Pollution | HARMFUL EFFECTS | HOW TO REDUCE IT |
|---|---|---|
| Vehicle horns and engines | Lack of sleep and constant fatigue | Silence zones near hospitals and schools |
| Loudspeakers and DJ systems | Anxiety, irritation and stress | Plant trees along roads and around homes |
| Construction and industrial machines | High blood pressure | Silencers on vehicles, generators and machines |
| Bursting of firecrackers | Temporary or permanent hearing loss | Shift noisy factories away from housing areas |
| TV, radio and music at high volume | Poor concentration and memory | Keep TV and music at low volume |
| Aircraft flying overhead | Headache and heart problems | Use ear plugs / ear muffs in noisy workplaces |
TREES AS SOUND ABSORBERS
Planting trees along roads and around buildings is one of the simplest and most effective ways of fighting noise pollution. Leaves and branches absorb sound energy instead of reflecting it, so a green belt acts as a natural noise barrier. Trees fight air pollution and noise pollution at the same time.
Quick Revision
Everything you must remember, in one place
| Concept | Key Point to Remember |
|---|---|
| Production of sound | Sound is produced by vibrating objects. No vibration, no sound. |
| Human voice | Produced by the voice box (larynx) using two vocal cords. |
| Vocal cord length | Men ≈ 20 mm · Women ≈ 15 mm · Children ≈ 5–6 mm. Shorter → shriller. |
| Medium | Sound needs a medium. It cannot travel through vacuum. |
| Speed order | Solid > Liquid > Gas. In air ≈ 344 m/s; in water ≈ 1,500 m/s; in steel ≈ 5,100 m/s. |
| Parts of the ear | Pinna → ear canal → eardrum → three bones → cochlea → auditory nerve → brain. |
| Amplitude | Maximum displacement from rest position. Decides loudness. |
| Frequency | Vibrations per second. Unit: hertz (Hz). Decides pitch. |
| Time period | Time for one complete vibration. Frequency = 1 ÷ Time period. |
| Loudness | Measured in decibel (dB). Proportional to the square of amplitude. |
| Audible range | 20 Hz to 20,000 Hz for humans. |
| Infrasonic | Below 20 Hz. Heard by elephants, whales, rhinoceroses. |
| Ultrasonic | Above 20,000 Hz. Heard by dogs, bats, dolphins. Used in ultrasound scans and SONAR. |
| Music vs noise | Music = regular, periodic, pleasant. Noise = irregular, non-periodic, unpleasant. |
| Noise pollution | Excessive/unwanted sound. Above 80 dB is harmful. Reduce with trees, silencers, low volume. |
Exercise Zone
6 question types · 10 questions each · 60 questions with answers
Type 1 | Answer in One Sentence
Q1. How is sound produced?
Ans. Sound is produced by the vibration of objects.
Q2. Name the organ that produces sound in human beings.
Ans. The voice box or larynx produces sound in human beings.
Q3. What is the SI unit of frequency?
Ans. The SI unit of frequency is the hertz (Hz).
Q4. In which unit is the loudness of sound measured?
Ans. Loudness of sound is measured in decibels (dB).
Q5. What is the audible range of frequency for human beings?
Ans. The audible range for human beings is from 20 Hz to 20,000 Hz.
Q6. By what other name is the eardrum known?
Ans. The eardrum is also known as the tympanic membrane.
Q7. Which characteristic of a vibration determines the pitch of sound?
Ans. The frequency of vibration determines the pitch of sound.
Q8. Write the relation between frequency and time period.
Ans. Frequency is the reciprocal of time period, that is, frequency = 1 ÷ time period.
Q9. What is an unpleasant sound called?
Ans. An unpleasant sound is called noise.
Q10. Name any two animals that can hear ultrasonic sound.
Ans. Dogs and bats can hear ultrasonic sound.
Type 2 | Answer in Two Sentences
Q1. What is a vibration?
Ans. A vibration is the rapid to-and-fro motion of an object about its mean or rest position. Every vibrating object disturbs the particles of the surrounding medium and thereby produces sound.
Q2. Why can we not hear any sound on the Moon?
Ans. There is no atmosphere on the Moon, so a vacuum exists on its surface. Since sound needs a material medium with particles to travel through, no sound can reach our ears there.
Q3. What is amplitude?
Ans. Amplitude is the maximum distance through which a vibrating object moves away from its rest position. It determines the loudness of the sound produced.
Q4. Why is the voice of a child shriller than that of an adult man?
Ans. A child’s vocal cords are only about 5 to 6 mm long, while a man’s are about 20 mm long. Shorter cords vibrate at a higher frequency, and higher frequency produces a shriller, higher-pitched voice.
Q5. What is the function of the pinna?
Ans. The pinna is the visible outer flap of the ear that collects sound from the surroundings. It funnels the collected sound into the ear canal, which carries it towards the eardrum.
Q6. Distinguish between infrasonic and ultrasonic sound.
Ans. Sound of frequency below 20 Hz is called infrasonic and is heard by animals such as elephants and whales. Sound of frequency above 20,000 Hz is called ultrasonic and is heard by animals such as dogs and bats.
Q7. Why do we hear a scratching sound more clearly through a table than through air?
Ans. The particles in a solid such as wood are packed much more closely together than the particles in air. They therefore pass the disturbance along faster and with less loss of energy, so the sound reaches the ear more clearly.
Q8. What is noise pollution?
Ans. Noise pollution is the presence of excessive or unwanted sound in our environment. It is caused mainly by vehicle horns, loudspeakers, machines and firecrackers.
Q9. A pendulum takes 0.4 second to complete one oscillation. Find its frequency.
Ans. Frequency = 1 ÷ time period = 1 ÷ 0.4 = 2.5. Therefore the frequency of the pendulum is 2.5 Hz.
Q10. How is music different from noise?
Ans. Music is produced by regular and periodic vibrations and is pleasant to the ear. Noise is produced by irregular and non-periodic vibrations and is unpleasant and disturbing.
Type 3 | Answer Yes or No, with Reason
Q1. Can sound travel through a vacuum?
Ans. No. A vacuum contains no particles, and sound needs particles of a medium to pass the vibration from one point to the next.
Q2. Can sound travel through water?
Ans. Yes. Water is a liquid medium made of particles, so it can carry sound — this is exactly how dolphins and whales communicate under the sea.
Q3. Does loudness depend on frequency?
Ans. No. Loudness depends on the amplitude of vibration; it is the pitch, not the loudness, that depends on frequency.
Q4. Can a human being hear a sound of frequency 5 Hz?
Ans. No. A frequency of 5 Hz is infrasonic, which lies below the human audible range of 20 Hz to 20,000 Hz.
Q5. Do particles of the medium travel along with the sound from the source to your ear?
Ans. No. Each particle only vibrates about its own fixed position and passes the energy to the next particle; it is the disturbance that travels, not the matter.
Q6. Is a dog whistle audible to human beings?
Ans. No. A dog whistle produces ultrasonic sound above 20,000 Hz, which lies beyond the upper limit of human hearing, although dogs can hear it easily.
Q7. Does sound travel faster in steel than in air?
Ans. Yes. The particles of steel are packed far more tightly than those of air, so they transfer the vibration much faster — about 5,100 m/s in steel compared with about 344 m/s in air.
Q8. Can loud music be considered noise?
Ans. Yes. Even pleasant music becomes noise when it is too loud or played at an inappropriate time, because it then disturbs people and can damage the ears.
Q9. Does planting trees along roadsides help reduce noise pollution?
Ans. Yes. Leaves and branches absorb sound energy rather than reflecting it, so a belt of trees acts as a natural barrier that lowers the noise reaching nearby homes.
Q10. Will a bell ringing inside a jar be heard after all the air is pumped out?
Ans. No. Removing the air creates a vacuum inside the jar, and with no particles left to carry the vibration the sound cannot reach us, even though we can still see the hammer striking the bell.
Type 4 | True or False (Correct the False Statements)
Q1. Sound can travel through vacuum.
Ans. FALSE. Correction: Sound cannot travel through vacuum, because a vacuum has no particles to carry the vibration.
Q2. Sound is produced by vibrating objects.
Ans. TRUE.
Q3. The loudness of sound is determined by its frequency.
Ans. FALSE. Correction: The loudness of sound is determined by its amplitude; frequency determines the pitch.
Q4. The unit of frequency is decibel.
Ans. FALSE. Correction: The unit of frequency is hertz (Hz); decibel is the unit of loudness.
Q5. Sound travels faster in air than in water.
Ans. FALSE. Correction: Sound travels faster in water than in air, because the particles of a liquid are packed more closely than those of a gas.
Q6. Human beings can hear sound of frequency 25,000 Hz.
Ans. FALSE. Correction: Human beings cannot hear 25,000 Hz, as it is ultrasonic and lies above the audible limit of 20,000 Hz.
Q7. The vocal cords of women are longer than those of men.
Ans. FALSE. Correction: The vocal cords of men are longer (about 20 mm) than those of women (about 15 mm), which is why men have deeper voices.
Q8. Music is produced by regular and periodic vibrations.
Ans. TRUE.
Q9. Elephants can hear infrasonic sound.
Ans. TRUE.
Q10. Sounds above 80 dB are safe for continuous listening.
Ans. FALSE. Correction: Sounds above 80 dB are physically painful and damaging to the ears when heard continuously.
Type 5 | Fill in the Blanks
Q1. Sound is produced by the __________ of an object.
Ans. vibration
Q2. The voice box in human beings is also called the __________.
Ans. larynx
Q3. Sound cannot travel through a __________.
Ans. vacuum
Q4. The loudness of sound depends on the __________ of vibration.
Ans. amplitude
Q5. The unit of frequency is __________.
Ans. hertz
Q6. The thin membrane stretched across the ear canal is called the __________.
Ans. eardrum
Q7. Loudness of sound is measured in __________.
Ans. decibel
Q8. The frequency of vibration determines the __________ of sound.
Ans. pitch
Q9. The upper limit of the human audible range is __________ Hz.
Ans. 20,000
Q10. Unpleasant sound produced by irregular vibrations is called __________.
Ans. noise
Type 6 | Answer in Four Sentences
Q1. Explain how sound is produced and how it reaches our ears.
Ans. Sound is produced when an object vibrates rapidly to and fro about its rest position. The vibrating object pushes and pulls the particles of the surrounding medium, creating a disturbance. This disturbance is passed from one particle to the next, travelling outward as a sound wave while the particles themselves stay in place. When the wave reaches our ear it makes the eardrum vibrate, and the brain finally interprets these vibrations as sound.
Q2. Describe the structure and working of the human voice box.
Ans. The voice box, or larynx, is situated at the upper end of the windpipe and can be felt as a small bump in the throat. Two stretched bands of muscle called vocal cords are fixed across it, leaving a narrow slit between them. When we speak, air from the lungs is forced through this slit, making the vocal cords vibrate and produce sound. Muscles attached to the cords can tighten or loosen them, allowing us to produce voices of different pitch and quality.
Q3. Why does sound travel fastest in solids and slowest in gases?
Ans. Sound travels by particles of the medium passing a disturbance from one to the next. In solids the particles are packed extremely close together, so the disturbance is handed on almost instantly, giving speeds of about 5,100 m/s in steel. In liquids the particles are a little farther apart, so sound slows to about 1,500 m/s in water. In gases the particles are widely separated and must travel some distance before colliding, so sound is slowest at about 344 m/s in air.
Q4. Describe the journey of sound through the human ear.
Ans. The pinna, the outer flap of the ear, collects sound from the surroundings and funnels it into the ear canal. The canal carries the sound to the eardrum, a thin stretched membrane that begins to vibrate. These vibrations are amplified by three tiny bones in the middle ear and passed on to the fluid-filled cochlea of the inner ear. The cochlea converts them into electrical signals, which the auditory nerve carries to the brain where they are interpreted as sound.
Q5. Differentiate clearly between loudness and pitch with examples.
Ans. Loudness tells us how strong or faint a sound is and depends entirely on the amplitude of vibration, being measured in decibels. Pitch tells us how shrill or deep a sound is and depends entirely on the frequency of vibration, measured in hertz. A drum struck hard is loud but still low in pitch because its large membrane vibrates slowly with a large amplitude. A mosquito’s buzz is very soft yet very high in pitch, because its wings vibrate rapidly with a tiny amplitude.
Q6. Explain amplitude, time period and frequency, and state the relation between the last two.
Ans. Amplitude is the maximum distance a vibrating object moves away from its rest position, and it decides the loudness of the sound. Time period is the time taken to complete one full to-and-fro vibration, and it is measured in seconds. Frequency is the number of complete vibrations made in one second, and its unit is the hertz. Frequency and time period are reciprocals of each other, so frequency = 1 ÷ time period.
Q7. What are audible and inaudible sounds? Give examples of animals for each type.
Ans. Sounds with frequencies between 20 Hz and 20,000 Hz can be detected by the human ear and are called audible sounds. Frequencies below 20 Hz are called infrasonic and are inaudible to us, though elephants, whales and rhinoceroses can hear them. Frequencies above 20,000 Hz are called ultrasonic and are also inaudible to us, but dogs, bats and dolphins hear them easily. Bats even use ultrasonic squeaks and their returning echoes to navigate in complete darkness.
Q8. What is noise pollution? State its main causes.
Ans. Noise pollution is the presence of excessive or unwanted sound in our surroundings. Its main causes are the horns and engines of vehicles, loudspeakers and DJ systems, and machines used in construction and industry. Bursting firecrackers, aircraft flying overhead, and televisions or music systems played at high volume also add to it heavily. Because noise leaves behind no visible trace, it is a form of pollution that is very easy to overlook.
Q9. Describe the harmful effects of noise pollution on human health.
Ans. Continuous exposure to loud noise causes lack of sleep and leaves a person constantly tired and irritable. It raises anxiety and stress levels and can lead to high blood pressure, headaches and even heart problems. Students in noisy surroundings find it hard to concentrate and their memory suffers. Most seriously, noise above 80 dB heard over long periods can damage the delicate eardrum and cause temporary or even permanent hearing loss.
Q10. Suggest four practical measures to reduce noise pollution.
Ans. Trees should be planted along roadsides and around buildings, because leaves absorb sound energy and act as a natural noise barrier. Silencers should be fitted to vehicles, generators and industrial machines, and unnecessary use of horns should be avoided. Noisy factories and airports should be located well away from residential areas, and silence zones should be strictly enforced near hospitals and schools. Finally, people should keep televisions and music systems at a low volume, and workers in noisy places should always wear ear plugs or ear muffs.
