The World of Sound
FoundationSound is made by vibration and travels through solids, liquids and gases; pitch depends on how fast things vibrate, loudness is measured in decibels, and over 85 decibels for long harms hearing.
- Sound comes from vibration; no vibration, no sound.
- Sound travels through solids, liquids and gases, never a vacuum.
- Faster vibration means higher pitch.
文體小知識：說明文把聲音的科學一層層揭開。這一篇由振動講起，教你明白音調、分貝和保護聽覺的方法。
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1In the music room, a classmate plucks the guitar string, sees it flick back and forth rapidly, and hears a pleasant sound. Sound is made by vibration: drum skins tremble when struck, and vocal cords vibrate when we speak. When the vibration stops, the sound stops too — that is sound's first secret.
2How does the vibration reach our ears? A vibrating object pushes the air around it, and the push travels outward in rings, like ripples from a stone dropped in a pond, entering the ear canal and shaking the eardrum. Sound travels through solids, liquids and gases, but not through a vacuum: put a ringing alarm clock inside a jar with the air pumped out, and the bell falls silent.
3Why does a thick guitar string sound deep while a thin one sounds clear? Pitch depends on how fast something vibrates: the faster the vibration, the higher the pitch; the slower, the lower. Short, thin, tightly stretched strings vibrate faster and sound high; long, thick, loose strings vibrate slower and sound low. The difference between a bass and a soprano is exactly this difference in vibration speed.
4Loudness is measured in decibels. A quiet library is about 40 decibels and ordinary chat about 60; staying above 85 decibels for long — such as road drills or roaring concerts — damages hearing. Harsh, annoying sounds that disturb life are noise, mostly from traffic, construction and over-loud speakers.
5Everyone can protect their hearing: follow the 60-60 rule with earphones — volume under sixty percent, no longer than sixty minutes at a time; wear earplugs or earmuffs near construction sites and at concerts; and when your ears ring, leave the noise and rest at once. Guard your ears well, and you will enjoy the world's lovely sounds for a lifetime.
1Summary 重點摘要
Sound is made by vibration and travels through solids, liquids and gases; pitch depends on how fast things vibrate, loudness is measured in decibels, and over 85 decibels for long harms hearing.
2Vocabulary cards Vocabulary
The rapid back-and-forth movement of an object — the source of sound.
The vibrating object that makes a sound, such as a drum skin or vocal cords.
The substance sound travels through — solid, liquid or gas.
The thin membrane at the end of the ear canal that picks up sound vibrations.
How high or low a sound is, set by vibration speed — faster means higher.
How loud a sound is, measured in decibels.
The unit of loudness: a library is about 40 decibels, a concert over 100.
Harsh, annoying sound that disturbs life, such as construction noise.
Small plugs worn in the ears to block noise and protect hearing.
Ways to guard hearing, such as lowering volume, avoiding noise and wearing earplugs.
3Step by step Steps
- Step 1: Discover that sound comes from vibrationTry small experiments: rest a hand on your throat while speaking and feel your vocal cords vibrate; strike a tuning fork and dip it in water, and the splashes prove it vibrates; pluck a guitar string and see it blur into a blur of motion. All show that sound is born of vibration. Press the vibrating string with a finger and the sound stops at once — vibration stops, sound stops. Look for things that make sound and watch how they vibrate.
- Step 2: See that sound needs a mediumA vibrating source pushes the material around it, passing the vibration outward layer by layer — that material is the medium. Sound travels through gases, liquids and solids: we usually hear through air; knock on a desk with your ear against it and the sound comes through the solid more clearly; fish in water can hear sounds from the shore. But sound cannot travel through a vacuum, for a vacuum has nothing to vibrate — which is why space is silent.
- Step 3: Understand pitch and vibration speedPitch is how high or low a sound is, set by how fast the source vibrates. The faster the vibration — the higher the frequency — the higher the pitch; the slower, the lower. Shorter, thinner, tighter strings vibrate faster and sound higher; longer, thicker, looser ones sound lower. Blow across a bottle: the more water inside, the shorter the air column, the higher the note. In an orchestra the violin sounds higher than the cello exactly because its strings are shorter and thinner.
- Step 4: Know loudness and decibelsLoudness is how big a sound is, measured in decibels. A quiet countryside is about 30 decibels, a library about 40, ordinary conversation about 60, a busy road about 80, and a plane taking off over 100. Doctors warn that staying above 85 decibels for long damages the hearing cells, and the damage cannot be repaired. Download a decibel-meter app and measure your classroom, playground and market — be a little sound researcher.
- Step 5: Learn what causes noise and what it doesAny harsh, irritating sound that disturbs life and rest is noise. In Hong Kong, noise mainly comes from traffic, construction, aircraft and over-loud speakers. Long-term noise trouble causes sleeplessness, irritability and poor concentration, lowers learning efficiency, and damages hearing. The government therefore controls night-time construction noise by law and builds noise barriers along busy roads to protect the public's peace.
- Step 6: Learn to protect your hearingDamaged hearing never heals, so protect your ears from childhood. Follow the 60-60 rule with earphones: volume under sixty percent of maximum, and no more than sixty minutes at a stretch. Wear earplugs or earmuffs in noisy places; do not stand beside the speakers at concerts; if your ears ring or sounds blur, leave the noise at once and tell an adult. Treasure your ears, and the world's lovely sounds will stay with you for life.
5Worked example Example
Example: Wing and her family sat near the speakers at a concert where the sound reached 105 decibels; her ears rang all night afterwards. Explain this with decibel knowledge and suggest ways to protect hearing.
- Decibels measure loudness; long exposure above 85 decibels damages hearing.
- The concert's 105 decibels far exceed 85, enough to fatigue or even harm hearing in a short time.
- The ringing in her ears is a warning sign that her hearing has been overworked and needs rest.
- Protection: sit farther from the speakers, wear earplugs or earmuffs, and take breaks for the ears.
- Daily life also calls for the 60-60 rule with earphones — guard hearing from childhood.
- Answer: Loudness is measured in decibels, and long exposure above 85 decibels harms hearing; the concert reached 105 decibels, far beyond the safe level, so Wing's ears rang all night — a warning sign of strained hearing. Next time she should sit farther from the speakers, wear earplugs or earmuffs and give her ears breaks; in daily life she should also follow the 60-60 rule with earphones to protect her hearing.
6Common mistakes Mistakes
7Quick check Quick check
Q1What produces sound?
Q2Through which three kinds of medium can sound travel?
Q3When vibration gets faster, what happens to pitch?
Q4Which unit measures loudness?
Q5Long exposure above how many decibels damages hearing?
8Recap Recap
- Sound comes from vibration; no vibration, no sound.
- Sound travels through solids, liquids and gases, never a vacuum.
- Faster vibration means higher pitch.
- Loudness is in decibels; over 85 for long harms hearing.
- Guard hearing: 60-60 rule, avoid noise, wear earplugs when needed.