Wave Motion – Take a string and mark it with different colors at equal intervals. Attach one end of the string with a hook and stretch the string by holding its other end in your hand. Start oscillating, the horizontally stretched string, vertically up and down briskly, waves can be seen as shown in the fig. 12.2.
If the colored markings are carefully observed, you will see that they are vibrating about their mean positions as the waves travel down the string. At a particular time, it can be observed that the markings rather than being in the same state of vibration, are in different states along their vibratory path.
We can conclude from this experiment that by moving the free end up and down a disturbance is generated and transferred to the other parts of the string which one after the other start vibrating and they start exhibiting vibratory motion about their mean position as the wave travel down the string. Thus disturbance travels along with the string in the form of waves.
From the above experiments, we can define wave motion as follows:
Wave motion in a medium is due to the generated disturbance which causes the constituent particles to repeat it’s to and fro motion about its mean position in equal interval of time, and this disturbance is passed over from one end of the medium to the other.
From the above experiments we also observe that the particles of the medium play an important role in the generation of waves. They perform a special type of wave motion known as “Simple Harmonic Motion”.