Mechanical Waves. Mechanical waves are created by the vibration of objects. Mechanical waves can be either transverse or longitudinal.

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1 Mechanical Waves Mechanical waves are created by the vibration of objects. Mechanical waves can be either transverse or longitudinal. When an object vibrates, its vibrations form mechanical waves that can travel through solids, liquids, or gases in a series of ripples that spread away from the object and disturb nearby particles. As each particle is disturbed, it collides with the particle next to it. In this way, the wave moves through the material. An example of a mechanical wave can be seen when a loud, low sound, such as music with heavy bass, creates ripples in the liquid inside a nearby glass. Mechanical waves can be classified based on how they affect the particles of a medium. The two classifications of waves based on this criterion are transverse waves and longitudinal waves. Clip provided by Education Clip Library with permission from ITN Source Transverse Mechanical Waves

2 A few types of mechanical waves are transverse. A wave moving along a rope is an example of a transverse mechanical wave. When a transverse wave moves through a medium, the medium moves at right angles to the direction in which the wave travels. A man moves one end of a string connecting tennis balls up and down. The wave moves from left to right, but each tennis ball oscillates up and down. The diagram below shows some of the characteristics of a transverse wave. Some important characteristics of transverse waves are discussed below. Wavelength the distance between one wave crest and the next (or between one wave trough and the next). Vibrations with long wavelengths also have lower frequencies than vibrations with shorter wavelengths. This is because fewer of the longer-wavelength waves can travel a particular distance in a set amount of time.

3 Frequency the number of complete waves or cycles that pass a fixed point in a specific unit of time. If a high frequency wave and a low frequency wave are traveling past the same point, more cycles of the high frequency wave will pass the point in the same amount of time. Amplitude the size of the displacement or change caused by the wave. At any given frequency, it takes more energy to create a wave with larger amplitude than to create a wave with smaller amplitude. Speed a measurement of how fast a wave passes through a medium. The more tightly bound to each other the particles of a substance are, the faster a mechanical wave will travel through that substance. Crest the point on a transverse wave with the greatest positive displacement from equilibrium. In other words, a crest is the highest point of a wave (one wavelength). Trough the point on a transverse wave with the greatest negative displacement from equilibrium. In other words, a trough is the lowest point of a wave (one wavelength). Longitudinal Waves The diagram below shows some of the wave characteristics of a longitudinal wave. Each square represents an object, like a particle of matter, carrying the energy of the wave. Sound waves are longitudinal waves when passing through liquids and gases but can be transverse when passing through solids. When a longitudinal wave travels through a medium, the medium moves back and forth in the same direction in which the wave travels. The diagram below shows a longitudinal wave carrying sound through the air.

4 A knock on a door causes sound waves to travel through air particles. The wave moves from left to right, and each particle oscillates left and right. Some important characteristics of a longitudinal wave are discussed below. Wavelength the distance from one point of compression to the next on a longitudinal wave (or from one point of rarefaction to the next on the wave). Vibrations with long wavelengths also have lower frequencies than vibrations with shorter wavelengths. This is because fewer of the longer-wavelength waves can travel a particular distance in a set amount of time. Frequency the number of complete waves or cycles that pass a fixed point in a specific unit of time. High frequency sound waves have higher pitch than low frequency waves. For example, sound created by striking a bass drum has a lower frequency and lower pitch than a sound created by a bird's song. Amplitude the size of the displacement or change caused by the wave. The larger the amplitude of a sound wave, the louder the sound. At any given frequency, it takes more energy to create a sound wave with larger amplitude than to create a wave with smaller amplitude. Waves with large amplitudes show more compression at points of compression and more rarefaction at points of rarefaction than waves with small amplitudes. Speed a measurement of how fast a wave passes through a medium. The more tightly bound to each other the molecules of a substance are, the faster a mechanical wave will travel through that substance. Since particles in a solid are often bound to each other more tightly than particles in a liquid or gas, sound waves and seismic waves commonly travel rapidly through solids, slower through

5 liquids, and slowest through gases. Sound waves cannot travel through a vacuum, such as deep space, because there is no matter for the waves to be transmitted through. Compression the area of a longitudinal wave in which the molecules are the most crowded together. The compression point of a longitudinal wave is similar to the crest of a transverse wave. Rarefaction the area of a longitudinal wave in which the molecules are the most spread apart. The rarefaction point of a longitudinal wave is similar to the trough of a transverse wave. Comment on Lesson Prev Next Copyright 2013 Edmentum - All rights reserved.