What are called waves ? Mention their importance.

Explanation

When a pebble (small sphere of marble) is dropped in a pond of still water, disturbance is produced in the water surface at that position. Now this disturbance does not remain confined at that position, but moves radially outward on the surface of water forming concentric circles. This gives us a feeling as if water is moving away from origin of disturbance. This is an illusion because in reality water particles on any circle, simply oscillate about their respective equilibrium positions. Here disturbance moves ahead on the surface of water because of elasticity property of a medium. Please note that there is no shifting of medium.
Definition of wave : "The patterns which move without the actual physical transfer or flow of matter as a whole, are called waves." In general motion of disturbance either in medium or in vacuum is called wave (or sometimes wavebeat.)
When we speak, sound moves away from us without any flow of air, from one part to another part of air medium.
During the propagation of a wave, particles of medium receive energy turn by turn, causing displacements in them about their respective equilibrium positions, depending upon type of disturbance. Thus along with the energy, information in the input signal can also be transferred by the waves from one point to another.
During routine talk, our vocal cord becomes transmitter of .sound and our ears become detector (or receiver) of sound.
Our long distance communications depend on the transmission, propagation and reception of signals in the form of waves. During a telephone call, our voice (sound wave) is first converted into such an electrical signal which can be transmitted by the transmitter. These transmitted signals propagate through transmission channel or line (which may be copper wire, optical fibre, atmosphere or vacuum in the outer space). If the distance is very large then electrical signal is converted into light signal or electromagnetic wave.
Long distance communication also involves use of artificial satellites. At the receiving end, detection of original signal is made by following above steps in reverse order, to obtain information in required form and strength. (Detailed explanation about this communication process will be given in std. 12)
Importance of waves in daily life :
(1) All humans can see the world all around with the help of visible light which propagates in the form of waves.
(2) All humans can hear with the help of sound which also propagates in the form of waves.
(3) All humans feel the warmth with the help of sun light which also propagates in the form of waves.
Modern communication is based upon production, transmission and reception of radio waves which propagate in the form of electricmagnetic waves.
Effects shown by streams of fast moving fundamental particles are very much like waves of certain wavelength. (depending upon their mass and speed.) Such waves are called "Matter Waves."