As represented by the sinusoidal curve, the pressure variation in a sound wave repeats itself in space over a specific distance. Wavelength, period, and frequencyįigure 1C is another representation of the sound wave illustrated in Figure 1B. As a theoretical model, it helps to elucidate many of the properties of a sound wave. A wave of single frequency would be heard as a pure sound such as that generated by a tuning fork that has been lightly struck. As such, it is not perfectly representative of sound (see below Circular and spherical waves). A plane wave is a wave that propagates through space as a plane, rather than as a sphere of increasing radius. Plane wavesĪ discussion of sound waves and their propagation can begin with an examination of a plane wave of a single frequency passing through the air. What force slows motion? For every action there is an equal and opposite what? There’s nothing E = mc square about taking this physics quiz. 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.
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. 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.Ī sound wave thus consists of alternating compressions and rarefactions, or regions of high pressure and low pressure, moving at a certain speed. 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. 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. Watch a suspended vibrating spring to learn about the propagation of sound waves See all videos for this article 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. 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.
There are two basic types of wave, transverse and longitudinal, differentiated by the way in which the wave is propagated. The study of sound should begin with the properties of sound waves. 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. Sound, a mechanical disturbance from a state of equilibrium that propagates through an elastic material medium.
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