📚 Introduction to Sound | 声音入门
Sound is a form of energy produced by vibrations. When an object vibrates, it disturbs the particles around it, and this disturbance travels through a medium as a wave. Understanding sound is important because it explains how we hear, how musical instruments work, and how technologies such as sonar and ultrasound operate.
声音是由振动产生的一种能量形式。物体振动时，会扰动周围的粒子，这种扰动以波的形式通过介质传播。理解声音非常重要，因为它能解释我们如何听到声音、乐器如何发声，以及声呐和超声波等技术的工作原理。
In this KS3 CIE physics topic, you will learn how sound is made, how it travels, and how we describe sound waves using terms such as frequency, amplitude, wavelength, and speed.
在这个 KS3 CIE 物理主题中，你将学习声音是如何产生的、如何传播，以及如何使用频率、振幅、波长和速度等术语来描述声波。
1. What Is Sound? | 什么是声音？
Sound is a form of energy that we detect with our ears. It is produced when an object vibrates, such as a guitar string, a drum skin, or the vocal cords in your throat.
声音是我们用耳朵感知的一种能量形式。当物体振动时就会产生声音，例如吉他琴弦、鼓皮或喉咙中的声带。
These vibrations pass energy to nearby particles, creating a disturbance that travels away from the source. Without a vibration, there is no sound.
这些振动将能量传递给附近的粒子，形成从声源向外传播的扰动。没有振动，就没有声音。
Musical instruments produce sound in different ways: string instruments vibrate strings, wind instruments vibrate air columns, and percussion instruments vibrate a stretched skin or solid surface.
乐器以不同的方式产生声音：弦乐器振动琴弦，管乐器振动空气柱，打击乐器振动绷紧的皮面或固体表面。
2. Sound Is a Longitudinal Wave | 声音是一种纵波
Sound travels as a longitudinal wave. In a longitudinal wave, the particles of the medium vibrate in the same direction as the wave travels.
声音以纵波形式传播。在纵波中，介质粒子的振动方向与波的传播方向相同。
The wave is made up of compressions, where particles are squashed together, and rarefactions, where particles are spread apart. These regions move through the medium, carrying energy but not moving the particles over long distances.
纵波由密部和疏部组成。密部是粒子被挤压在一起的区域，疏部是粒子分散开的区域。这些区域在介质中移动，传递能量，但粒子本身并不会远距离移动。
This is different from a transverse wave, where particles vibrate at right angles to the direction of wave travel. Light and water waves are transverse, but sound in air is longitudinal.
这与横波不同。在横波中，粒子的振动方向与波的传播方向垂直。光波和水波是横波，但空气中的声波是纵波。
3. Sound Needs a Medium | 声音需要介质
Sound cannot travel through a vacuum. It needs a medium such as a solid, liquid, or gas because it relies on particles passing vibrations to one another.
声音不能在真空中传播。它需要固体、液体或气体等介质，因为声音依靠粒子相互传递振动。
The bell jar experiment demonstrates this. When air is pumped out of a jar containing a ringing bell, the sound becomes quieter and eventually disappears, even though the bell is still vibrating.
钟罩实验证明了这一点。把装有响铃的玻璃罩中的空气抽走，声音会逐渐变弱并最终消失，尽管铃仍在振动。
In space, there is no air, so astronauts cannot hear sounds directly. They must use radio communication because radio waves do not need a medium.
在太空中没有空气，因此宇航员无法直接听到声音。他们必须使用无线电通信，因为无线电波不需要介质。
4. Speed of Sound in Different Media | 声音在不同介质中的速度
Sound travels at different speeds in different materials. In general, it travels fastest in solids, slower in liquids, and slowest in gases.
声音在不同材料中的传播速度不同。一般来说，声音在固体中传播最快，在液体中较慢，在气体中最慢。
This happens because particles in a solid are packed closely together, so vibrations are passed on quickly. In a gas, the particles are far apart, so energy transfer takes more time.
这是因为固体中的粒子排列紧密，振动可以很快地传递。而在气体中，粒子相距很远，能量传递需要更长时间。
| Material | State | Speed of sound (m/s) |
|---|---|---|
| Steel | Solid | about 5000 |
| Water | Liquid | about 1500 |
| Air | Gas | about 340 |
Typical examination values are approximately 340 m/s in air, 1500 m/s in water, and 5000 m/s in steel. You may be asked to compare these speeds.
考试中常见的典型数值大约为：空气中 340 m/s，水中 1500 m/s，钢中 5000 m/s。你可能会被要求比较这些速度。
v = f × λ
In this equation, v is the wave speed in metres per second (m/s), f is frequency in hertz (Hz), and λ is wavelength in metres (m).
在这个公式中，v 是波速，单位为米每秒 (m/s)；f 是频率，单位为赫兹 (Hz)；λ 是波长，单位为米 (m)。
5. Frequency and Pitch | 频率与音调
Frequency is the number of complete vibrations or waves produced per second. It is measured in hertz (Hz).
频率是每秒产生的完整振动或波的个数，单位为赫兹 (Hz)。
A high frequency means the wave vibrates quickly and produces a high-pitched sound. A low frequency produces a low-pitched sound.
频率高表示振动快，产生高音调的声音；频率低则产生低音调的声音。
For example, a piccolo produces high-frequency sound waves, while a tuba produces low-frequency sound waves. A mosquito buzz has a high pitch, while thunder has a low pitch.
例如，短笛产生高频声波，而大号产生低频声波。蚊子的嗡嗡声音调高，雷声则音调低。
6. Amplitude and Loudness | 振幅与响度
Amplitude is the maximum distance a particle moves from its resting position as a wave passes. It is linked to the amount of energy carried by the wave.
振幅是波经过时粒子偏离平衡位置的最大距离，它与波携带的能量大小有关。
A sound wave with a larger amplitude carries more energy and sounds louder. A smaller amplitude sounds quieter.
振幅越大的声波携带的能量越多，听起来越响；振幅越小，声音越轻。
Loudness is measured in decibels (dB). Quiet sounds have low decibel values, while very loud sounds can damage hearing. Sounds above about 85 dB can be harmful if heard for a long time.
响度以分贝 (dB) 为单位。轻声的分贝值较低，而非常响的声音可能损伤听力。长时间听超过约 85 dB 的声音可能有害。
7. Showing Sound Waves on an Oscilloscope | 在示波器上显示声波
An oscilloscope can display sound waves as a voltage-time graph. This allows us to compare pitch and loudness visually.
示波器可以将声波显示为电压-时间图像，帮助我们从视觉上比较音调和响度。
A high-pitched sound produces a wave with many cycles across the screen, so the wavelength is short and the frequency is high.
高音调的声音在屏幕上显示为多个周期，因此波长较短，频率较高。
A low-pitched sound produces fewer cycles across the screen, so the wavelength is long and the frequency is low.
低音调的声音在屏幕上显示为较少周期，因此波长较长，频率较低。
A loud sound produces a wave with a large amplitude, meaning tall peaks and deep troughs. A quiet sound produces a smaller amplitude.
响的声音产生大振幅的波，即高峰和深谷；轻的声音则产生较小的振幅。
8. Human Hearing Range | 人类听觉范围
The human ear can normally hear sounds in the frequency range from about 20 Hz to 20 000 Hz (20 kHz).
人类耳朵通常能听到约 20 Hz 到 20 000 Hz (20 kHz) 频率范围内的声音。
Sounds above 20 000 Hz are called ultrasound. Sounds below 20 Hz are called infrasound. Humans cannot hear either of these, but some animals can.
频率高于 20 000 Hz 的声音称为超声波，低于 20 Hz 的称为次声波。人类听不到这两种声音，但某些动物可以听到。
Hearing range often decreases with age, especially for high-frequency sounds. This is why older people may struggle to hear very high notes.
听觉范围常常随年龄增长而缩小，尤其是对高频声音的感知。这就是为什么老年人可能难以听到很高音调的声音。
9. How the Ear Works | 耳朵如何工作
The ear is the organ that detects sound waves and converts them into electrical signals for the brain. It has three main parts: the outer ear, the middle ear, and the inner ear.
耳朵是探测声波并将其转换为电信号传给大脑的器官。它分为三个主要部分：外耳、中耳和内耳。
Sound waves enter the outer ear and travel down the ear canal to the eardrum. The eardrum vibrates, and these vibrations pass through three small bones called ossicles.
声波进入外耳，沿着耳道传到鼓膜。鼓膜振动，这些振动通过三块称为听小骨的小骨头传递。
The vibrations then reach the cochlea in the inner ear. The cochlea turns the vibrations into electrical signals that travel along the auditory nerve to the brain.
振动随后到达内耳的耳蜗。耳蜗将振动转化为电信号，电信号沿听神经传到大脑。
10. Echoes and Reflection of Sound | 回声与声音的反射
When sound waves hit a hard, flat surface, they can be reflected. A reflected sound that is heard after the original sound is called an echo.
当声波遇到坚硬平坦的表面时，会发生反射。在原声之后听到的反射声称为回声。
Echoes are used by ships and submarines in sonar systems. A pulse of sound is sent out, and the time taken for the echo to return is used to calculate distance.
船只和潜艇在声呐系统中利用回声。发出一个声脉冲后，根据回声返回所需的时间来计算距离。
Soft surfaces, such as curtains and carpets, absorb sound and reduce echoes. This is why concert halls use soft materials to control sound quality.
柔软的表面（如窗帘和地毯）会吸收声音并减少回声。这也是音乐厅使用软材料来控制音质的原因。
11. Ultrasound and Its Uses | 超声波及其应用
Ultrasound is sound with a frequency above 20 000 Hz, which is beyond the range of human hearing.
超声波是频率高于 20 000 Hz 的声音，超出了人类的听觉范围。
Ultrasound is used in medicine to scan unborn babies. It is safer than X-rays because it does not use ionising radiation.
超声波在医学上用于扫描胎儿。它比 X 射线更安全，因为它不产生电离辐射。
It is also used in industry to clean delicate objects, in physiotherapy, and in sonar to detect fish or map the sea floor.
超声波还用于工业上清洁精密物体、物理治疗，以及声呐探测鱼群或绘制海底地图。
Bats and dolphins use ultrasound naturally for navigation and hunting. They send out high-frequency clicks and listen for echoes to build a picture of their surroundings.
蝙蝠和海豚天生利用超声波进行导航和捕猎。它们发出高频咔哒声，并聆听回声来构建周围环境的图像。
12. Key Summary Table | 核心总结表
| Quantity | What it affects | Unit |
|---|---|---|
| Frequency | Pitch | hertz (Hz) |
| Amplitude | Loudness | decibel (dB) or metre (m) |
| Wave speed | How fast sound travels | m/s |
| Wavelength | Distance between two compressions | metre (m) |
Remember that sound is a longitudinal wave, cannot travel through a vacuum, and travels fastest in solids. The speed of sound in air is about 340 m/s.
请记住：声音是一种纵波，不能在真空中传播，并且在固体中传播最快。声音在空气中的速度约为 340 m/s。
Frequency determines pitch, amplitude determines loudness, and the human hearing range is about 20 Hz to 20 kHz. Ultrasound refers to sounds above this range and has many practical uses.
频率决定音调，振幅决定响度，人类的听觉范围约为 20 Hz 到 20 kHz。超过这个范围的声音称为超声波，它有许多实际用途。
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