Sound

Sound is a form of energy. It is a mechanical wave. It is caused by the vibrations of the particles. Each time a particle vibrates, its vibration excites our ear and the nerve send impulses to our brain and the brain senses it.
Sound propagates in two ways. 1) as a longitudinal wave and 2) as a transverse wave.

Waves: Waves are periodic disturbances in a medium. Energy is carried from one place to another as waves. Thats ones reason waves are used to obtain energy.

Longitudinal Waves: Waves in which particles move along the direction of the wave. Its a simple mechanism.
Lets assume particles of air to be straight lines like these ' |  |  |  |  |  |  |  | '. When particles have to move, they move back and forth like oscillations. There are two stages in movement of particles as longitudinal waves. Compressions and Rarefactions.

Compressions: when the particles move front, the particles in front of them are not in motion. So the particles in motion move very close to them and their vibrations are transferred. Now the particles that are rest start moving. Before the particles move, the particles behind them are very close to them, and are compressed.
                                                           |  |  |  |  |  |  |  |  | | | | | |||||||||| | | | | |  |  |  |  |  |

                                                                                            movement of particles 

                                                                                             ------------>>>>>>

Rarefactions: Now the particles which were in motion from the beginning return back to their original positions. This creates a gap between the particles coming back to their original positions and the particles moving front.
                                                           |  |  |  |  |  |  ||||         |           |         |  |  |  ||||
                                                                     movement of particles
                                                                                             <<<<<<------------
The combination of these two phenomenon is what leads to a longitudinal wave.

Longitudinal Wave

Transverse Waves: Waves in which particles move perpendicular to the direction of propagation of the wave. The simplest example is light wave or any other electromagnetic wave.

Transverse Wave

The ripples on the water are also examples of transverse wave.

Properties of Transverse Waves:

1. Amplitude(A): It is the maximum displacement of a particle from its mean position.
2. Oscillation: One complete cycle or vibration or one set of crest and trough.
3. Frequency: Number of oscillations in one minute. It is measured in hertz(Hz) where 1 Hz = 1 cycle/s 
4. Time Period(T): Time taken for one oscillation. Time Period and frequency are reciprocals of each other
                                                  
5. Wavelength( λ): It is the distance between two crests or troughs.

A sounds can be differentiated by its charaterstics. 

Three main characteristics of a Sound wave is: 

•  Loudness or Intensity:
  Loudness is because of greater amplitude. As amplitude increases, the energy of a wave also increases. We can surely differentiate between a loud and a soft sound.It is the magnitude of sound intensity.
  Intensity is the average amount of energy transported per unit area of a surface normal to the direction of propagation.
• Frequency or Pitch:
  If a waves has a higher frequency, then it is said to be shriller. If its frequency is less, then its said to be feeble. Two sounds of the same loudness or intensity can be differentiated by the difference in their frequency.
  We can differentiate between the sound of 512Hz and 256Hz tuning fork. The 512Hz tuning force is shriller.
• Timbre or Quality: 
  Two waves of the same loudness and frequency might differ in their wave forms. Timbre is also called tone quality and tone color.
  We can surely distinguish between the sound produced by a violin and a trumpet. It is because of the fact that their wave forms are different.
                        

The Speed of sound is 343.2 m/s in air. In water it is 1497 m/s. In steel, its velocity is 5930 m/s.