Vibration, in mechanics, is the rapid “to-and-fro” motion of an object. Almost everything vibrates, though the vibrations may be too weak, too fast, or too slow for us to detect. Vibration occurs during earthquakes and when the oceans move up and down causing the tides. An automobile vibrates as a result of repeated explosions in the cylinders of its engine. Many sounds are produced by vibrating objects.
Vibrations can be used to perform many useful tasks. When we tap a salt shaker, for example, we use vibrations to make the salt flow. Workers use devices that produce vibrations to pack down soil under roadways. In medicine, vibrators are used to treat sore muscles.
Vibrations can also cause problems for people and machines. Vibrations at certain rates and intensities cause discomfort. Too much vibration can cause people to lose their ability to concentrate. In machines, vibrations can cause noise, wear, and breakage.
Engineers have developed ways of correcting vibration problems. They may use elastic materials or springs to reduce the effects of vibration. For example, automobiles are equipped with pneumatic (air-filled) tires and shock absorbers to absorb the vibrations caused by traveling over rough roads. Ventilating fans in buildings are often mounted on springs.
Vibrations can be described by their amplitude and their frequency. Amplitude is the distance the vibrating object travels from a position of rest. Frequency is the number of complete vibrations during a certain period, usually one second. Frequency is measured in a unit called the hertz. Most people can hear vibrations with frequencies from 20 to 20,000 hertz.
Vibrations can be classified as free or forced, depending on whether an outside force keeps the vibration going. A guitar string, for example, vibrates freely after it is plucked. On the other hand, the vibration of a violin string is forced while the bow is drawn over it.
