📚 The Physics of Sound: Frequency, Pitch, and the 440 Hz Tone | 声音的物理：频率、音调与440赫兹标准音
Sound is all around us, from the music we hear to the words we speak. In IGCSE Science, understanding the physics of sound is essential for explaining how vibrations travel through a medium and how we perceive them. One particularly important frequency is 440 Hz, the standard tuning note used in music around the world.
声音无处不在，从我们听到的音乐到我们说出的话语。在IGCSE科学中，理解声音的物理原理对于解释振动如何通过介质传播以及我们如何感知它们至关重要。其中一个特别重要的频率是440赫兹，这是全世界音乐使用的标准调音音高。
1. What is Sound? | 什么是声音？
Sound is produced when an object vibrates. The vibrations transfer energy to the surrounding particles, causing them to vibrate back and forth. This chain of particle collisions carries sound energy through a medium such as air, water, or a solid.
声音是由物体振动产生的。振动将能量传递给周围的粒子，使它们来回振动。这种粒子碰撞的链条将声能通过空气、水或固体等介质传播。
Sound is a longitudinal wave. In a longitudinal wave, the particles of the medium vibrate parallel to the direction in which the wave travels. The wave consists of compressions, where particles are pushed together, and rarefactions, where particles are spread apart.
声音是一种纵波。在纵波中，介质粒子的振动方向与波的传播方向平行。声波由疏密相间的区域组成：密部（压缩区）是粒子被挤在一起的区域，疏部（稀疏区）是粒子分散开的区域。
- Compressions: regions of higher pressure and density.
密部：压强和密度较高的区域。 - Rarefactions: regions of lower pressure and density.
疏部：压强和密度较低的区域。 - Sound cannot travel through a vacuum because there are no particles to vibrate.
声音不能在真空中传播，因为没有粒子可以振动。
2. Wave Properties: Frequency and Amplitude | 波的属性：频率与振幅
Every sound wave has two key properties: frequency and amplitude. Frequency is the number of complete vibrations or waves produced per second. It is measured in hertz (Hz), where 1 Hz equals one vibration per second.
每个声波都有两个关键属性：频率和振幅。频率是每秒钟产生的完整振动或波的数量，单位是赫兹（Hz），1赫兹等于每秒一次振动。
Amplitude is the maximum displacement of a particle from its rest position. Larger amplitude means the wave carries more energy, which our ears perceive as a louder sound.
振幅是粒子偏离其平衡位置的最大位移。振幅越大，波携带的能量越多，我们的耳朵会将其感知为更响亮的声音。
The relationship between wave speed (v), frequency (f), and wavelength (λ) is given by the equation:
波速（v）、频率（f）和波长（λ）之间的关系由以下方程给出：
v = f × λ
This equation applies to all waves, including sound. If the wave speed is constant, increasing frequency results in a shorter wavelength.
该方程适用于所有波，包括声波。如果波速恒定，增大频率会导致波长变短。
3. The 440 Hz Standard | 440赫兹标准音
In music, the note A4 (the A above middle C) is standardised to a frequency of 440 Hz. This means that when a tuning fork or digital tuner produces 440 complete vibrations every second, it creates the pitch that orchestras use to tune their instruments.
在音乐中，A4音（中央C上方的A音）被标准化为440赫兹。这意味着当音叉或电子调音器每秒钟产生440次完整振动时，它发出的音高就是管弦乐队用来校音的标准音。
The international standard of 440 Hz was formally adopted in 1955 by the International Organization for Standardization (ISO 16). Before this, different countries and orchestras used tuning frequencies ranging anywhere from 415 Hz to 465 Hz, causing inconsistency in performances.
440赫兹的国际标准于1955年由国际标准化组织（ISO 16）正式采用。在此之前，不同国家和管弦乐队使用的调音频率从415赫兹到465赫兹不等，导致演出时音高不一致。
- Approved as ISO 16: a worldwide reference for musical pitch.
被批准为ISO 16：全球音乐音高的参考标准。 - Frequency of 440 Hz: means 440 wave cycles per second.
440赫兹的频率：意味着每秒440个波周期。 - Used for tuning pianos, violins, and other instruments.
用于为钢琴、小提琴等乐器调音。
4. Speed of Sound | 声速
The speed of sound in air at 20°C is approximately 343 metres per second (m/s). However, sound travels at different speeds through different materials. In general, sound travels faster in liquids and solids than in gases because particles are closer together, allowing energy to transfer more quickly.
在20°C的空气中，声速约为每秒343米（m/s）。然而，声音在不同材料中传播速度不同。一般来说，声音在液体和固体中比在气体中传播得快，因为粒子更紧密，能量传递更快。
The speed of sound is also affected by temperature. Warmer air has particles that move faster, so sound travels faster at higher temperatures. For example, at 0°C, the speed of sound in air is about 331 m/s, while at 20°C it is about 343 m/s.
声速也受温度影响。较暖的空气中粒子运动更快，因此声音在较高温度下传播得更快。例如，在0°C时，空气中声速约为331 m/s，而在20°C时约为343 m/s。
| Medium | Speed (m/s) |
|---|---|
| Air (0°C) | 331 |
| Air (20°C) | 343 |
| Water (20°C) | 1480 |
| Steel | 5000 |
5. Reflection and Echo | 反射与回声
When sound waves hit a hard, flat surface, they reflect, just like light waves. This reflection of sound is called an echo. The reflected sound reaches the listener after a delay because it has travelled to the surface and back.
当声波遇到坚硬、平坦的表面时，它们会发生反射，就像光波一样。这种声音的反射称为回声。反射的声音经过一段延迟后到达听者，因为它传播到表面然后又返回。
For a person to hear a distinct echo, the reflecting surface must be at least about 17 metres away. This is because the sound needs to travel to the surface and back, and the human ear can distinguish two sounds that are separated by at least 0.1 seconds. Given a speed of 340 m/s, the minimum total distance is 34 metres, so the one-way distance is 17 metres.
人们要听到清晰的回声，反射表面必须至少距离约17米。这是因为声音需要传播到表面再返回，而人耳能够区分至少间隔0.1秒的两个声音。以声速340 m/s计算，总距离最小为34米，因此单程距离为17米。
Echoes are used in sonar systems to locate objects under water. The device sends out a sound pulse and measures the time taken for the echo to return. Using the equation v = d/t, the distance can be calculated as d = v × t / 2.
回声被用于声呐系统来定位水下物体。设备发出声脉冲并测量回声返回所需的时间。利用公式 v = d/t，可以计算出距离 d = v × t / 2。
6. Loudness and Pitch | 响度与音调
Loudness and pitch are two different perceptual qualities of sound. Loudness is related to the amplitude of the sound wave: the greater the amplitude, the louder the sound. Pitch is related to frequency: the higher the frequency, the higher the pitch.
响度和音调是声音的两个不同感知属性。响度与声波的振幅有关：振幅越大，声音越响。音调与频率有关：频率越高，音调越高。
The human ear can normally hear frequencies from about 20 Hz to 20,000 Hz (20 kHz). Sounds above this range are called ultrasound, and sounds below this range are called infrasound. The range of human hearing varies with age, with older people often unable to hear the highest frequencies.
人耳通常能听到约20赫兹到20000赫兹（20 kHz）的频率范围。高于此范围的称为超声波，低于此范围的称为次声波。人类的听觉范围随年龄而变化，老年人通常无法听到最高频率的声音。
Volume is measured in decibels (dB). A whisper is about 20 dB, normal conversation is about 60 dB, and prolonged exposure to sounds above 85 dB can damage hearing.
音量用分贝（dB）测量。耳语约为20分贝，正常交谈约为60分贝，长期暴露在85分贝以上的声音中会损害听力。
- Higher amplitude → louder sound.
振幅越大 → 声音越响。 - Higher frequency → higher pitch.
频率越高 → 音调越高。 - Frequency range of human hearing: 20 Hz – 20 kHz.
人耳听觉频率范围：20 Hz – 20 kHz。
7. The Human Ear | 人耳
The human ear is divided into three parts: the outer ear, the middle ear, and the inner ear. The outer ear collects sound waves and funnels them down the ear canal to the eardrum, which is a thin membrane that vibrates when sound waves hit it.
人耳分为三部分：外耳、中耳和内耳。外耳收集声波并将其导入耳道，传到鼓膜。鼓膜是一层薄膜，当声波击中它时会产生振动。
The vibrations are then transferred through the three tiny bones of the middle ear (hammer, anvil, and stirrup) to the cochlea in the inner ear. The cochlea is filled with liquid and lined with tiny hair cells. As the liquid vibrates, the hair cells bend, converting the mechanical vibration into electrical signals.
振动随后通过中耳的三块小骨（锤骨、砧骨和镫骨）传导到内耳的耳蜗。耳蜗内充满液体，内壁排列着微小的毛细胞。当液体振动时，毛细胞弯曲，将机械振动转化为电信号。
These electrical signals are sent along the auditory nerve to the brain, where they are interpreted as sound. The brain can identify the pitch, loudness, and direction of the sound based on the pattern of signals.
这些电信号沿着听神经传送到大脑，在大脑中被解释为声音。大脑可以根据信号模式识别音调、响度和声音的方向。
8. Ultrasound and Infrasound | 超声波与次声波
Ultrasound is a sound wave with a frequency above 20,000 Hz. It cannot be heard by humans, but it can be used in many practical applications. In medicine, ultrasound scans use high-frequency sound waves to create images of the inside of the body, such as a developing foetus.
超声波是频率高于20000赫兹的声波。人类无法听到，但它有许多实际应用。在医学中，超声波扫描利用高频声波生成人体内部的图像，例如发育中的胎儿。
Ultrasound is also used in industry to clean delicate objects, to detect cracks in metal, and by bats and dolphins for navigation and hunting.
超声波还用于工业中清洗精密物体、检测金属中的裂缝，并且蝙蝠和海豚利用它进行导航和捕猎。
Infrasound is a sound wave with a frequency below 20 Hz. It can be produced by earthquakes, volcanoes, and large animals such as elephants. Some animals, including whales and elephants, use infrasound to communicate over long distances.
次声波是频率低于20赫兹的声波。它可能由地震、火山和大型动物（如大象）产生。一些动物（包括鲸鱼和大象）利用次声波进行远距离通信。
| Type | Frequency range | Example use |
|---|---|---|
| Infrasound | Below 20 Hz | Monitoring earthquakes |
| Audible sound | 20 Hz – 20 kHz | Speech and music |
| Ultrasound | Above 20 kHz | Medical scanning |
9. Sound in Communication | 声音在通信中的应用
Sound has been used for communication for thousands of years, from human speech to drum signals. Modern technology uses sound waves in telephones, microphones, and loudspeakers to transmit and reproduce audio signals.
几千年来，声音一直被用于通信，从人类语言到鼓声信号。现代技术在电话、麦克风和扬声器中使用声波来传输和重现音频信号。
A microphone converts sound waves into electrical signals. When sound waves hit the microphone’s diaphragm, it vibrates, generating a varying electrical wave that mirrors the original sound. A loudspeaker does the reverse: an electrical signal causes a coil and cone to vibrate, producing sound waves.
麦克风将声波转换为电信号。当声波击中麦克风的振膜时，振膜振动，产生与原始声音对应的变化电信号。扬声器则相反：电信号使线圈和纸盆振动，产生声波。
In digital communication, sound is sampled and encoded into binary numbers. A common sampling rate for high-quality audio is 44,100 samples per second, which is more than twice the highest audible frequency, satisfying the Nyquist theorem to avoid loss of information.
在数字通信中，声音被采样并编码为二进制数字。高质量音频常见的采样率为每秒44100次，这超过最高可听频率的两倍，满足奈奎斯特定理以避免信息丢失。
The 440 Hz tuning note is also used in telephone systems in some countries as a dial tone, helping to standardise audio signals. This connects the physics of sound directly to everyday technology.
在一些国家，440赫兹的调音音也被用作电话系统的拨号音，帮助标准化音频信号。这直接将声音的物理原理与日常科技联系起来。
10. Conclusion | 结论
Sound is a fascinating topic in IGCSE Science because it connects the physical wave model to real-world perception and technology. We have seen that frequency determines pitch, amplitude determines loudness, and the wave equation v = f × λ links the key properties together.
声音是IGCSE科学中一个引人入胜的主题，因为它将物理波动模型与真实世界的感知和技术联系起来。我们已经看到，频率决定音调，振幅决定响度，而波动方程 v = f × λ 将关键属性联系在一起。
The 440 Hz standard demonstrates how a specific scientific value has become a global convention in music and communication. Understanding sound, from echoes to ultrasound, allows us to appreciate both natural phenomena and engineered devices such as microphones and sonar.
440赫兹标准展示了一个特定的科学数值如何成为音乐和通信领域的全球惯例。理解声音，从回声到超声波，使我们能够欣赏自然现象以及麦克风、声呐等工程设备。
Master these concepts, and you will be well prepared for your Edexcel IGCSE Science examinations.
掌握这些概念，你将为Edexcel IGCSE科学考试做好充分准备。
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