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Sound waves in air (and any fluid medium) are longitudinal waves because particles of the medium through which the sound is transported vibrate parallel to the direction that the sound wave moves. A vibrating string can create longitudinal waves as depicted in the animation below. As the vibrating string moves in the forward direction, it ...
- Sound is a Pressure Wave
Sound waves traveling through a fluid such as air travel as...
- Sound is a Mechanical Wave
Production and Propagation of Sound Waves. The creation and...
- Simple Wave Simulator
The Simple Wave Simulator Interactive provides the learner...
- Sound is a Pressure Wave
- Overview
- Plane waves
- Wavelength, period, and frequency
sound, a mechanical disturbance from a state of equilibrium that propagates through an elastic material medium. A purely subjective definition of sound is also possible, as that which is perceived by the ear, but such a definition is not particularly illuminating and is unduly restrictive, for it is useful to speak of sounds that cannot be heard by the human ear, such as those that are produced by dog whistles or by sonar equipment.
The study of sound should begin with the properties of sound waves. There are two basic types of wave, transverse and longitudinal, differentiated by the way in which the wave is propagated. In a transverse wave, such as the wave generated in a stretched rope when one end is wiggled back and forth, the motion that constitutes the wave is perpendicular, or transverse, to the direction (along the rope) in which the wave is moving. An important family of transverse waves is generated by electromagnetic sources such as light or radio, in which the electric and magnetic fields constituting the wave oscillate perpendicular to the direction of propagation.
Sound propagates through air or other mediums as a longitudinal wave, in which the mechanical vibration constituting the wave occurs along the direction of propagation of the wave. A longitudinal wave can be created in a coiled spring by squeezing several of the turns together to form a compression and then releasing them, allowing the compression to travel the length of the spring. Air can be viewed as being composed of layers analogous to such coils, with a sound wave propagating as layers of air “push” and “pull” at one another much like the compression moving down the spring.
A sound wave thus consists of alternating compressions and rarefactions, or regions of high pressure and low pressure, moving at a certain speed. Put another way, it consists of a periodic (that is, oscillating or vibrating) variation of pressure occurring around the equilibrium pressure prevailing at a particular time and place. Equilibrium pressure and the sinusoidal variations caused by passage of a pure sound wave (that is, a wave of a single frequency) are represented in Figure 1A and 1B, respectively.
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A discussion of sound waves and their propagation can begin with an examination of a plane wave of a single frequency passing through the air. A plane wave is a wave that propagates through space as a plane, rather than as a sphere of increasing radius. As such, it is not perfectly representative of sound (see below Circular and spherical waves). A...
Figure 1C is another representation of the sound wave illustrated in Figure 1B. As represented by the sinusoidal curve, the pressure variation in a sound wave repeats itself in space over a specific distance. This distance is known as the wavelength of the sound, usually measured in metres and represented by λ. As the wave propagates through the air, one full wavelength takes a certain time period to pass a specific point in space; this period, represented by T, is usually measured in fractions of a second. In addition, during each one-second time interval, a certain number of wavelengths pass a point in space. Known as the frequency of the sound wave, the number of wavelengths passing per second is traditionally measured in hertz or kilohertz and is represented by f.
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There is an inverse relation between a wave’s frequency and its period, such that
Note that sound waves in air are longitudinal, and in the figure, the wave propagates in the positive x-direction and the molecules oscillate parallel to the direction in which the wave propagates. Figure \(\PageIndex{2}\): (a) A vibrating cone of a speaker, moving in the positive x-direction, compresses the air in front of it and expands the air behind it.
the sound from the trumpet comes from a vibrating column of air created by buzzing lips of the trumpeter. A sound wave is a longitudinal wave. When an object vibrates it produces a longitudinal ...
Sep 12, 2023 · How Sound Waves Travel. Sound, being a longitudinal wave, makes the air molecules move in the same direction as the wave itself. For example, when a drum is hit, the drum’s surface vibrates, causing the nearby air molecules to move back and forth along the line of the wave.
Nov 6, 2024 · Some media support only longitudinal waves, others support only transverse waves, while yet others support both types. Light waves are purely transverse, while sound waves are purely longitudinal. Ocean waves are a peculiar mixture of transverse and longitudinal, with parcels of water moving in elliptical trajectories as waves pass.
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Jul 23, 2023 · Artwork: Sound waves and ocean waves compared. Top: Sound waves are longitudinal waves: the air moves back and forth along the same line as the wave travels, making alternate patterns of compressions and rarefactions. Bottom: Ocean waves are transverse waves: the water moves back and forth at right angles to the line in which the wave travels.
