# Mechanical Waves

Updated on June 29, 2015

## Mechanical Waves

The wave concept in modern science is of up most importance. A wave is a motion that carries energy from one place to another in a medium. A wave in water is probably the most familiar kind of wave but there are many other kinds of waves all around us. For example, voice travel to our ears in the form of longitudinal waves. Radio and television programmes reach our homes in the forms of electromagnetic waves. Light rays, X-rays and Gamma rays also travel as waves.

When a stone is thrown in the pond of water, the waves are created on the surface of water by the up and down movement of water molecules. The shape of the waves is usually like the shape of hills and valleys. The hills are called creates and the valleys are known as troughs. When a wave moves along a medium, there are two things to watch: the movement of the wave and the movement of medium. The particles of the medium in which waves are produced vibrate to and fro about their mean position. The particles of the medium only vibrate; they do not travel with the wave. Wave in fact is a result of periodic motion of the particles.

For mechanical waves to travel, the medium should have the property of elasticity. This property makes the particles to come back to the original position. Medium should have the inertia but least force of friction. These properties are possessed by all materials such as air, water, steel etc.

Some kinds of waves do not require materials medium to travel. These are called electromagnetic waves. Light waves are electromagnetic waves and can travel even in space.

Mechanical waves are of two types namely transverse waves and longitudinal waves.

Transverse waves are those in which the particles of the medium vibrate to and from about their mean position perpendicular to the direction of wave propagation. The waves generated on the surface of water or in strings are transverse in nature. Longitudinal waves are those in which the particles of the medium vibrate in the direction of wave propagation. These waves are created as a result of compressions and rarefactions. Sound waves are longitudinal in nature. Waves generated in the air are longitudinal in nature. Longitudinal waves can travel in solids, liquids and gases.

Some Definitions

Frequency: number of vibrations per second is called the frequency of the vibrating body. Frequency is expressed in cycles per second or hertz. It is expressed as n.

Time Period: the time taken by a body to complete on vibration is called its time period. It is measured in seconds and expressed as T. the relation between time period and frequency is given by T-1/n

Amplitude: the amplitude of a wave is the amount it rises or falls from its usual position.

Phase: phase is defined as the instantaneous position and direction of motion of the wave.

Wavelength: it is defined as the distance between the two nearest points in the same phase or the distance between the two consecutive crests or troughs, or compressions or rarefactions. It is expressed by λ.

Speed of the wave: the distance traveled by the wave in the one second is called its speed. If via is the speed of a wave having wavelength λ and frequency n then v= n λ.

Generally waves travel in air with the speed of 340 meters per second. Generally, waves are measured in angstrom units (A) or (A0). Actually, one angstrom unit = 0.1nanometers which is approximately one-third the size of a carbon atom. In fact, one angstrom is equal to the diameter of a hydrogen atom, the smallest element on earth. However, the bigger waves are measured in meters, centimeters and millimeters.

Pitch: sounds may be generally characterized by pitch, loudness and quality. The perceived pitch of a sound is just the ear’s response to frequency, i.e. for most practical purposes, the pitch is just the frequency. The pitch perception of the human ear is understood to operate basically by the place theory, with some sharpening mechanism necessary to explain the resolution of human pitch perception. The just noticeable difference in pitch is expressed in cents and the standard figure for the human ear is 5 cents.

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