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


Comments

Post a Comment

Popular posts from this blog

EAST COAST CANAL SYSTEM AND ITS IMPORTANCE FOR INLAND NAVIGATION & INLAND WATER TRANSPORT

Image
1. Introduction: - The East Coast Canal (ECC) System providing the connectivity between Kolkata Port and Cuttack along with other trade canters in the coastal districts of Odisha through Inland Water Transport during the British era was the lifeline of Odisha being the first mode of surface transport. The canal system was developed during nineteenth century primarily for inland navigation connecting the River Hooghly at Goenkhali in West Bengal  72 km from Kolkata Port with the river Matai at Charbatia, Odisha. The waterways system from Charbatia was extended up to False Point port (harbour) on the estuary of the river Mahanadi near Paradeep port through the delta rivers from the major river systems like Brahmani, Baitarani, Mahanadi and the creeks. The connectivity of ECC from the then riverine & sea port facilities at Balasore, Chandbali, Dhamra, Mangoljodi, False Point harbour to Cuttack and the important trade centers through delta and coastal irrigation canal systems facil...
Read more

WHY WATER WETS AND MERCURY DOES NOT?

Any substance has some physical/ chemical properties which include having positive/ negative electronic balance. If there are two substances next to each other, depending on the positive/negative nature, the molecules may attract or repel. Water in a glass – water molecules near glass get attracted hence it rises above the water level at the water edge. This property is called adhesion. So water forms a concave surface in a glass tube. An extreme of this nature is when a very narrow glass tube is inserted in a glass of water, water level in the narrow tube rises above the glass water level. This is known as capillary action. The attraction between molecules of the same substance is called cohesion. This gives rise to surface tension. If water/ mercury is in air, the cohesive forces are more than adhesive forces with air and so water or mercury takes the shape of a spherical droplet on its own, sphere being the least energy consuming shape. But in contact with glass, wate...
Read more

IMPORTANCE OF PROTOCOL ON INLAND WATER TRADE & TRANSIT (PIWT&T) BETWEEN INDIA & BANGLADESH FOR NORTH-EAST REGION

Image
  1. Introduction: Prior to the partition of India in 1947, the trade and commerce of the NER (North-Eastern Region) with the rest of India used to pass through the territories of East Bengal, what is now Bangladesh. After the independence, rail and river transit across the erstwhile East Pakistan continued till 1965 with an agreement. But, consequence of the Indo-Pak war & subsequent war for liberation of Bangladesh, inland navigation to & through the country was suspended. On signing of the Protocol on Inland Water Transit & Trade (PIWT & T) on 1st November 1972 in pursuance of Article VIII of the Trade Agreement between Government of India and Bangladesh, the Inland navigation for Exim cargo between the countries and transit cargo from mainland to NER & vice versa, using the waterways of Bangladesh could be revived.   2. Protocol Routes and Ports of call: -Initially four prominent routes (named as Indo-Bangladesh Protocol routes) on the major river syste...
Read more