📚 KS3 Science: Sound Waves and Hearing | KS3科学：声波与听觉
Sound waves are all around us, from speech and music to traffic noise. This KS3 revision guide explains how sound is made, how it travels, and how we hear it.
声波无处不在——从说话、音乐到交通噪音。本 KS3 复习指南将解释声音是如何产生的、如何传播的，以及我们如何听到声音。
1. What Is Sound? | 什么是声音
Sound is a form of energy carried by vibrations. When an object vibrates, it pushes and pulls nearby particles, creating a wave that carries energy away from the source.
声音是由振动携带的一种能量形式。物体振动时，会推拉周围的粒子，产生从声源向外传播的波。
Sound waves are longitudinal waves. In a longitudinal wave, particles vibrate back and forth in the same direction as the wave travels.
声波是纵波。在纵波中，粒子沿波传播的方向来回振动。
- Example: A guitar string vibrates when plucked.
- 示例：拨动吉他弦时，弦会振动。
2. How Sound Travels | 声音如何传播
A sound wave travels by making particles in a medium bunch together in compressions and spread out in rarefactions.
声波通过使介质中的粒子聚集形成密部、分散形成疏部来传播。
Sound cannot travel through a vacuum because there are no particles to pass on the vibrations.
声音不能在真空中传播，因为真空中没有粒子来传递振动。
| Feature | 中文 | Description |
|---|---|---|
| Compression | 密部 | Region where particles are close together |
| Rarefaction | 疏部 | Region where particles are spread apart |
3. Sound Needs a Medium | 声音需要介质
Sound can travel through solids, liquids and gases, but it travels at different speeds in each medium.
声音可以在固体、液体和气体中传播，但在不同介质中的传播速度不同。
Sound travels fastest in solids, slower in liquids, and slowest in gases because particles are closer together in solids, so vibrations pass along more quickly.
声音在固体中传播最快，在液体中较慢，在气体中最慢，因为固体中的粒子靠得更近，振动传递得更快。
| Medium | 中文 | Speed of sound (m/s) |
|---|---|---|
| Air (20°C) | 空气（20°C） | 340 |
| Water | 水 | 1500 |
| Steel | 钢 | 5000 |
4. Speed of Sound | 声速
In air at room temperature, sound travels at approximately 340 m/s. This means it takes about 3 seconds to travel 1 kilometre.
在室温空气中，声速约为 340 m/s。这意味着声音传播 1 公里约需 3 秒。
The speed of sound increases with temperature because particles move faster and collide more often.
声速随温度升高而增加，因为粒子运动更快、碰撞更频繁。
speed = distance ÷ time
For all waves, speed, frequency and wavelength are linked by the equation:
对于所有波，波速、频率和波长之间的关系为：
v = f × λ
Where v is speed in m/s, f is frequency in hertz (Hz), and λ is wavelength in metres (m).
其中 v 是速度（m/s），f 是频率（Hz），λ 是波长（m）。
5. Frequency and Pitch | 频率与音调
Pitch is how high or low a sound seems. It depends on the frequency of the sound wave.
音调是声音听起来的高低。它取决于声波的频率。
High frequency means high pitch; low frequency means low pitch. Frequency is measured in hertz (Hz), which means number of vibrations per second.
频率高则音调高；频率低则音调低。频率的单位是赫兹（Hz），表示每秒振动的次数。
Humans can normally hear sounds from about 20 Hz to 20,000 Hz (20 kHz). Sounds above this range are called ultrasound; sounds below are infrasound.
人类通常能听到约 20 Hz 到 20,000 Hz（20 kHz）的声音。高于此范围的声波叫超声波，低于此范围的是次声波。
6. Amplitude and Loudness | 振幅与响度
Loudness is how loud or quiet a sound seems. It depends on the amplitude of the sound wave.
响度是声音听起来的大小。它取决于声波的振幅。
A larger amplitude transfers more energy, so the sound is louder. Amplitude is the maximum distance a particle moves from its resting position.
振幅越大传递的能量越多，因此声音越响。振幅是粒子离开平衡位置的最大距离。
We measure loudness in decibels (dB). Sounds above 85 dB can damage hearing over a long time.
我们用分贝（dB）来测量响度。长期暴露在 85 dB 以上的声音中会损害听力。
7. The Ear and Hearing | 耳朵与听觉
The human ear converts sound waves into electrical signals that the brain interprets as sound.
人耳把声波转换成电信号，由大脑解读为声音。
The outer ear collects sound and directs it down the ear canal to the eardrum. The eardrum vibrates, and tiny bones in the middle ear pass the vibrations to the cochlea in the inner ear.
外耳收集声音并把它导入耳道到达鼓膜。鼓膜振动，中耳的小骨头把振动传到内耳的耳蜗。
In the cochlea, hair cells change the vibrations into electrical signals. The auditory nerve carries these signals to
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