The vibration that goes through a matter is called sound. The sound gets produced when something sends energy waves to a human ear. Sound travels in all directions from the point of its origin. Understand with an example that when something is dropped in till water, concentric waves arise from that object. Similar is the case of sound. It travels from the source point to all directions in the form of a wave. The sound gets faint as the distance increases from the sources of sound. We can listen to sounds for which the vibration per second is between 20 to 20,000 times. Sound needs a medium to propagate from one point to another. It is the reason that sound cannot travel through a vacuum.

• Echo: Echo is the sound produced after the sound reflects from a distant object, such as a hill. It gets created after the original sound ceases.
• Reverberation: This is the phenomenon that occurs when the original sound gets mixed with the reflection of the sound. It happens if the distance is less than 17m, and the authentic sound gets mixed with the reflected sound.
• Reflection: Reflection means the bounce-back of sound after striking from the surface, such as a hill. Reflection and absorption of sound occur when sound strikes a surface. It means that some sound waves get absorbed in the reflecting surface.
• Pitch: Pitch is the feature of sound that helps distinguish the acute note from a flat note.
• Loudness: Loudness is the property of a loud sound that distinguishes it from a faint sound. It varies directly with the amplitude, and Decibels is its unit of measurement.

• The movement of sound from one place to another is known as the propagation of sound.
• The propagation of sound occurs with the help of particles present in the medium having to-and-from motion.
• The vibrating body creates a disturbance in the form of vibration. This disturbance passes from one particle to another in the medium and carries sound from source to the ear.

• Sound needs a medium to propagate.
• A medium is a matter through which the sound gets transmitted. It can be gas, liquid, or solid.
• Sound does not travel in a complete absence of substance or matter as it needs matter to travel. A physical medium must be there for sound to travel anywhere.
• A mechanical wave is a wave that needs a medium for propagation. The sound never travels in a vacuum.

• Wave is a phenomenon where energy transfers from one place to another with no direct connection between both the points.
• Sound travels as a wave from one point to another due to the particle oscillation phenomenon.
• The medium’s particles do not travel from one place to another but vibrate only.

Based on the propagation direction, waves get divided into two different types: Longitudinal and Transverse.

1. Longitudinal Waves:
   The waves where the particles have to-and-from motion towards the wave’s direction are called Longitudinal Waves.
2. Transverse Waves:
   The waves where particles do to-and-from motion perpendicular to the direction of the wave are called Transverse Waves.Sound as a Longitudinal WaveThe particles in the medium move to and fro while the sound wave propagates, making the sound wave a longitudinal wave. 

   Compression and Rarefaction

   The sound wave propagates by forming compressions and rarefactions. Each wave consists of a series of regular compressions and rarefactions.

   1. Compression:
      Compression is the high-pressure area created as the vibrating particle moves forward by pushing the air. Compression of a wave is the area having high density and high pressure, where particles get crowded and represent the upper part of the curve known as the crest.
   2. Rarefaction:
      Rarefaction is the area of low pressure that gets created as the vibrating particle moves backwards. These are the areas where pressure and density are lower and particles are far apart. Rarefaction is represented as the lower part of the curve and is called valleys or troughs.

Sound waves have mainly below characteristics:

• Amplitude:
  Amplitude is the height of the tough or crest of the wave. It implies how high the crest of the wave is. This maximum displacement of the sound wave above or below the central line is the sound wave’s amplitude. A symbol represents the amplitude. The amplitude of the sound wave depends upon how loud the sound is. A louder sound wave has a high amplitude than a soft sound wave.
• Wavelength:
  Wavelength is the distance between two consecutive rarefactions or compressions. In simple words, it represents the distance that repeats throughout the wave. Lambda represents the wavelength.
• Frequency:
  The frequency of a wave is the number of vibrations that a particle completes in a second. The below formula can be used to calculate the frequency of the wave:
  Frequency = Number of Oscillations / Total Time
  It can be calculated by finding the number of rarefactions or compressions that occur within a second. nu symbol represents the frequency.
• Velocity:
  Velocity is the distance travelled by a sound wave in one second. The speed with which the sound wave travel’s rarefactions and compressions is the sound wave’s velocity. The relative speed of sound in different mediums is different. V symbol represents the Velocity.

Finally, the sound is the vibration that propagates as waves from the source to all directions. Sound needs a medium to propagate. The medium can be solid, gas, or liquid. Waves are of two types, viz. Longitudinal and transverse. Sound waves are longitudinal as particles in the matter travel to and fro. Sound waves have amplitude, frequency, wavelength, and velocity that defines how loud the sound is.

1. What is Sound?
   It is a vibration, which passes through a matter.
2. What are the types of waves?
   The sound has two waves; Longitudinal Waves and Transverse Waves.
3. Does Sound travel through a Vacuum?
   The sound doesn’t travel through a Vacuum. It needs matter or substance to travel.
4. Name the terminologies related to the Sound!
   Echo, Reflection, Reverberation, Loudness, and Pitch.
5. What are the characteristics of Sound waves?
   Amplitude, Wavelength, Frequency, and Velocity.