Tyler Wynn
Sound is a vibration that propagates as an acoustic wave through gases, liquids, or solids. Sound waves are characterised by their frequency and amplitude, which determine pitch and loudness, respectively. The speed of sound depends on the medium through which it travels, with sound waves travelling faster in warmer conditions. Sound is also used by many species for communication, navigation, and detecting danger. Humans have developed technology to generate, record, transmit, and broadcast sound. The study of sound begins with the properties of sound waves, which can be transverse or longitudinal.
| Characteristics | Values |
|---|---|
| Definition | Sound is a vibration that propagates as an acoustic wave through a transmission medium such as a gas, liquid or solid. |
| Medium | The matter that supports the sound, e.g. water, air, etc. |
| Speed | Depends on the type of medium the sound waves travel through. For example, in dry air at 20°C, the speed of sound is 343 m/s, and in room temperature seawater, it is about 1531 m/s. |
| Wave Type | Sound waves are longitudinal waves, also called compression waves. They can also be transverse waves. |
| Frequency | The number of compressions per second, which relates to the pitch of the sound. Measured in Hertz (Hz). |
| Amplitude | Refers to the height of the wave and determines the loudness of a sound. Measured in decibels (dB). |
| Pitch | The quality that enables us to judge sounds as "higher" or "lower". A high pitch causes molecules to rapidly oscillate, while a low pitch causes slower oscillation. |
| Loudness | How "loud" or "soft" a sound is, determined by the totalled number of auditory nerve stimulations over short cyclic time periods. |
| Timbre | Tone color or "feel" of the sound, which allows humans to quickly identify sounds. |
| Duration | How "long" or "short" a sound is, relating to onset and offset signals created by nerve responses. |
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What You'll Learn
Sound as a mechanical disturbance
Sound is a mechanical disturbance from a state of equilibrium that propagates through an elastic material medium. This medium can be a gas, liquid, or solid, and sound travels through it in the form of a pressure wave. When an object vibrates, it causes the particles in the medium around it to vibrate, creating a chain reaction of sound wave vibrations. These vibrations are characterised by areas of high and low pressure, known as compressions and rarefactions, respectively. The speed of sound depends on the type of medium it travels through, with sound waves travelling faster in warmer conditions.
Sound waves are composed of two basic elements: frequency and amplitude. Frequency refers to the number of compressions per second and is measured in Hertz (Hz). The higher the frequency, the higher the pitch. For example, a sound wave with a frequency of 20 Hz will have a lower pitch than one with a frequency of 20 kHz. The physical property of frequency is perceived as pitch, with higher frequencies corresponding to higher pitches.
Amplitude, on the other hand, determines the loudness of a sound wave. It is measured in decibels (dB) and represents the height of the wave. A greater amplitude results in a louder sound. However, it is important to note that human perception of loudness is not solely based on amplitude. For instance, sounds at very low and very high frequencies may be perceived as softer, even if they have the same amplitude as sounds in the middle frequencies.
Sound waves can be categorised into two types: transverse and longitudinal. Transverse waves are characterised by motion that is perpendicular to the direction in which the wave is moving. These waves are commonly generated by electromagnetic sources such as light or radio. On the other hand, longitudinal waves, also called compression waves, are formed by vibrations in the air, which we can hear. These waves consist of compressions and rarefactions that propagate through the medium.
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How sound is produced
Sound is produced when an object vibrates, causing the medium (water, air, etc.) around it to vibrate. These vibrations in the air are called travelling longitudinal waves, which we hear. Sound waves consist of areas of high and low pressure called compressions and rarefactions, respectively. The wavelength and the speed of the wave determine the pitch, or frequency of the sound.
Frequency is defined as the number of compressions per second, which directly relates to the pitch of the sound. As the frequency increases, so does the pitch. The frequency is measured in Hertz (Hz). For example, the note A above middle C has a frequency of 440 Hz. The speed of sound depends on the type of medium the sound waves travel through. In dry air at 20°C, the speed of sound is 343 m/s. In room temperature seawater, sound waves travel at about 1531 m/s.
The amplitude of a sound wave determines its relative loudness. In music, the loudness of a note is called its dynamic level. In physics, the amplitude of sound waves is measured in decibels (dB). Higher amplitudes correspond with louder sounds, while shorter amplitudes correspond with quieter sounds.
Sound waves can also be transverse, where the motion that constitutes the wave is perpendicular, or transverse, to the direction in which the wave is moving. An example of a transverse wave is the wave generated in a stretched rope when one end is wiggled back and forth. An important family of transverse waves is generated by electromagnetic sources such as light or radio.
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How sound travels
Sound is a mechanical disturbance that propagates through an elastic material medium, such as a gas, liquid, or solid. It is caused by vibrations that travel in a wave pattern and can be transmitted through gases, plasma, and liquids as longitudinal waves, also known as compression waves. Through solids, sound can be transmitted as both longitudinal and transverse waves.
Sound waves move by vibrating objects and these objects, in turn, vibrate other surrounding objects, carrying the sound along. The further away from the original source of a sound you are, the weaker the waves become until they no longer have the energy to vibrate other particles. Sound waves require particles to bounce off and cannot travel through a vacuum.
The speed at which sound moves depends on the medium through which it is travelling. For example, sound travels faster through hotter, denser air. The viscosity of the medium also determines the rate at which sound is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible.
The physical properties of sound waves, such as frequency and amplitude, determine how they are perceived by the human ear. Shorter, faster-moving sound waves produce high-frequency, sharp noises, whereas larger, slower-moving waves make low-frequency, bassy tones. The human ear does not have a flat spectral response, so sound pressures are often frequency-weighted so that the measured level matches perceived levels more closely.
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Sound as a pressure wave
Sound is a mechanical disturbance from a state of equilibrium that propagates through an elastic material medium. This medium can be a gas, liquid, or solid, and sound travels through it in the form of a pressure wave.
When an object vibrates, it causes the surrounding molecules in the medium to vibrate, creating a chain reaction of sound wave vibrations throughout the medium. These vibrations are called travelling longitudinal waves, or compression waves, and they consist of areas of high and low pressure called compressions and rarefactions, respectively. The compressions and rarefactions can be visualised on a diagram as a wave with varying shades of light and dark representing the pressure levels. The high-pressure areas are the dark regions, and the low-pressure areas are the light regions. This pattern repeats indefinitely.
The speed of sound depends on the type of medium it travels through. For example, in dry air at 20°C, sound travels at 343 m/s, while in room-temperature seawater, it moves much faster at about 1531 m/s. The speed of sound is also influenced by temperature, generally travelling faster in warmer conditions.
The frequency of a sound wave is defined as the number of compressions per second and is measured in Hertz (Hz). As the frequency increases, so does the pitch. For example, the note A above middle C has a frequency of 440 Hz. The wavelength and frequency of a sound wave determine its pitch, with longer wavelengths resulting in lower pitches. The amplitude of a sound wave, or its "height," indicates how loud the sound is. Greater amplitude means the sound will be louder.
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Sound perception
Sound waves are mechanical disturbances that propagate through a medium, such as air or water, as longitudinal waves or compression waves. These waves consist of alternating areas of compression (high pressure) and rarefaction (low pressure), which create variations in air pressure that the human ear can detect. The ear detects these variations in air pressure through the eardrum, which vibrates in response to the sound waves, creating a corresponding electrical signal that is sent to the brain.
The brain interprets these electrical signals as sound, allowing us to perceive the world around us. Our brains are incredibly adept at recognizing and interpreting specific features of sound waves, such as frequency and amplitude, which correspond to pitch and loudness, respectively. The frequency of a sound wave is measured in Hertz (Hz) and relates to the pitch of the sound, with higher frequencies corresponding to higher pitches. Amplitude, on the other hand, determines the loudness of a sound, with greater amplitudes resulting in louder sounds.
In addition to pitch and loudness, our brains can also interpret the duration and timbre of a sound. Duration refers to how long or short a sound is, while timbre refers to the tone colour or "feel" of the sound, which allows us to differentiate between different sound sources. For example, the sound produced by a piano has a different timbre than that of a guitar, allowing us to quickly identify the source of the sound.
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Frequently asked questions
Sound is a mechanical disturbance from a state of equilibrium that propagates through an elastic material medium such as gases, liquids, or solids. Sound is produced when something vibrates, causing the medium around it to vibrate.
There are two basic types of waves: transverse and longitudinal. Transverse waves are characterised by motion that is perpendicular to the direction in which the wave is moving. On the other hand, longitudinal waves, also called compression waves, consist of areas of high and low pressure called compressions and rarefactions, respectively. The wavelength and the speed of the wave determine the pitch, or frequency of the sound.
Sound waves are registered by the human ear as vibrations in the medium, which are then processed by the brain. The four properties of sound that enable us to perceive it are pitch, dynamics (loudness or softness), timbre (tone colour), and duration.
