Ocean Waves


We know that ocean waves are transverse waves and carriers of energy over long distances. The characteristic of a transverse wave is that the direction of wave motion is perpendicular to the direction of wave oscillation which is not so in a longitudinal wave like a sound wave. Electromagnetic waves are also transverse waves.

 


 

Fig.1 orbital motion of water particles in a water wave

 


 

Fig.2 direction of velocity of water particle due to a wave


In deep ocean waves, water particle on the surface exhibit circular motion as shown in Fig.1. The particle velocity on top of a crest is towards the direction of wave motion whereas, in a trough, the particle velocity is in the opposite direction as shown in Fig.2. The velocity of water particles reduces exponentially as one goes down in depth and the wave effect vanishes after a certain depth.

Since there is a longitudinal motion of particles, why should ocean waves not be considered as a combination of transverse and longitudinal waves?

Gravin Pretor-Pinney writes in his book The Wave Watcher’s Comanion, in page 66-67,

While we can divide physical waves into transverse, longitudinal and torsional waves……the truth is that many real waves combine aspects of more than one type. Take ocean waves out at sea, for instance: those circular paths, along which the water moves as the wave passes through, are a combination of up-and-down and forward-and-back motion. The water may look like it just rises and falls with passing wave, but it actually combines transverse (up and down) with longitudinal (forward and back) movement, resultin in orbital motion.

 

By :: Prof. S. C. Misra

Comments are welcome, posted either here or mailed to:: misra1948@gmail.com


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