Wave Motion – Children are often seen dropping stones in the water while sitting by a pond and getting amused by the waves being produced in it.


Wave motion are not only produced on the surface of water, but when one end of the stretched rope is briskly moved up and down, waves can be seen being produced in the rope. Now –a- days, we are familiar with many different types of waves which are not visible but can be detected with sensitive equipments. Sound also reaches our ears in the form of waves. The heat and light that reaches us from the sun, also does this in the form of waves.

The broad-casting of radio and television programs is also made possible by the waves. The defects in the human body e.g, broken bones, tumors, bullets, can also be detected by a specific type of waves, known as x-rays, what are waves? How they are produced? How many types of waves are there? Answers of such questions are discussed in detail in this chapter with the aid of experimental observations.

wave motion

Experiment 1:

dip one end of a pencil at the edge of a tub containing water, rapidly move the pencil up and down vertically, the ripples emerge outwards of the surface of the water (fig. 12. 1).

Place some small pieces of a cardboard or a cork equally spaced, in the direction of the waves, and observe the movement of the pieces as the waves pass. You will see that every piece of the cardboard moves up and down about its mean positions.

They are not displaced forward from their original positions along with the water waves. The motion of these pieces about their mean positions is known as “Vibratory Motion”. If we examine the vibratory motion of all the pieces, it can be observed that they do not vibrate together but vibrate vertically at their own position one after the other.

In this experiment, the vibratory motion of the pencil produces disturbance in the constituent molecules of the water, due to which they start exhibiting vibratory motion about their mean position. Thus this disturbance is transferred along with the wave, and a visible water wave can be observed.

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