1.0 Introduction

  Sound Waves

• Infrasonic waves
• Audible waves
• Ultrasonic waves

1.0.1 Infrasonic waves

Sound wave is an example of longitudinal waves. In longitudinal wave the constituents of medium oscillate forward and backward in the direction of propagation of the waves. Due to this oscillation of air compression and rarefraction develops.

Sound waves can be classified in three groups according to their range of frequencies.

• Infrasonic waves
• Audible waves
• Ultrasonic waves

1.0.2 Infrasonic waves

Longitudinal waves having frequencies below 20 $Hz$ are called infrasonic waves.

Infrasonic waves cannot be heard by human beings.

Earthquakes produces infrasonic waves.

Animals such as whales, elephants, snakes etc uses infrasonic waves (infrasound) to communicate.

So, animals have been known to perceieve the infrasonic waves going through the earth by natural disasters and can be used as an early warning.

1.0.3 Audible waves

Longitudinal waves having frequencies lying between 20-20,000 $Hz$ are called audible waves.

1.0.4 Ultrasonic waves

Longitudinal waves having frequencies above 20,000 $Hz$ are called ultrasonic waves.

Features of ultrasonic waves:

• They are highly energetic.
• There speed of propagation depends on their frequencies
• They can be transmitted over long distances without any appreciable loss of energy.
• 
  

Application of ultrasonic waves:

• Determination of the depth of sea
• Detection of aircraft, submarines etc
• Ultrasonic waves are used to detect cracks or flaws in metal structures
• They are used for cleaning clothes and parts of watches etc
• Use to kill smaller animals like rats, fish, frog etc
• Ultrasonic waves are used to kill bacteria for sterlising milk

1.1 Shock waves

If the speed of the body body in air is greater than the speed of sound, then it is called supersonic waves.

Supersonic bodies leaves behind a conical region of disturbance which spreads continiously. Such disturbances is called as shock waves.

This shock waves carries huge energy. If it strikes a building then the building may be damaged.