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Wave Motion

Radars: A simple invention to protect a nation. Radar: A simple invention to protect a nation Radio detection and ranging (RADAR), is a device that is capable of transmitting an electro–magnetic wave and receive back a reflection from a target to analyse the position and characteristics of the target based on the reflected signal. What is a wave, how does it travel in a medium and what are its characteristics are discussed as we travel through this topic.

Learning objectives

After completing the topic, the student will be able to:

  • Understand the concept of transfer of energy from one system to another with or without the physical contact.
  • Probe for different types of waves and their importance to everyday science.
  • Explore and differentiate transverse and longitudinal waves and discuss their importance in everyday science.
  • Examine and correlate energy of the wave and its intensity to apply to real world scenarios.
  • Understand the basic difference between transmission and reflection of a wave.
  • Examine and investigate interference of waves and its applications in the real world.
  • Discuss the concept of a standing wave along with its characteristics and its importance in daily life situations.
Surfing wave Surfing- A surface water sport The surfer rides a surfboard on the crest and face of a wave, which carries him towards the shore. Waves suitable for surfing are found primarily in the ocean, but are also sometimes found in lakes and rivers.
Introduction

When an object moves in space, we can understand its motion fully by observing the changes in its co–ordinates with time. Linear motion and circular motion are simplest types of motions. In simple harmonic motion, an object moves up and down or back and forth around its mean position. Now if an object in up and down motion were connected to other objects, what would we observe? For simplicity, let us consider the object to be a small boy. He is holding hands with his friends, who are standing in one line. If the boy walks a few steps ahead, he pulls his friends along. Similarly, if he walks a few steps backwards, his friends are again dragged backwards. If the boy keeps on doing this back and forth motion (his own motion is actually simple harmonic motion), he generates oscillatory motion along the line of his friends, which is called wave motion.

So waves can occur whenever a system is disturbed from equilibrium and when the disturbance can travel, or propagate, from one region of the system to another. As a wave propagates, it carries energy. This is one of the most important phenomena in nature where the transfer of energy occurs from one point to another by wave motion. There are two types of waves: mechanical waves and electromagnetic waves.

Floating cork on water Floating cork on water While the cork floats, it doesn’t move away from its original position due to the ripple motion caused by dropping a stone.
Wave motion

Wave motion can be defined as vibratory or oscillatory disturbance in a medium where energy is transferred from one particle to another. It is interesting to note that in wave motion, the individual particles vibrate along their mean positions – they really do not migrate away! Only energy travels forward.

How wave motion carries only energy and does not displace matter from its mean position is demonstrated in a simple way. Take a large bowl of water. Float a cork on the surface away from the centre. Note its position. Now drop a stone in the bowl. You will see ripples forming on the water and extending outwards. The kinetic energy of the stone is transferred to the molecules of water, which oscillate up and down. The molecules make a periodic up and down motion, without being permanently displaced from their mean position. The energy is transferred from one molecule to the other via their intra molecular bonds. The cork will start bobbing up and down without changing its actual position from the centre of the bowl.

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