What is Sound? Sound is typically defined as " the vibrations that travel through the air or another medium and can be heard when they are perceived by a brain and reach a ear". Source of sound is always the vibrations of an object. Sound is transmitted in the form of waves with altering increase and decrease in pressure. Sound requires a medium. It cannot travel in vacuum because there is nothing to compress and stretch. The chapter Sound Basics describes some of the significant characteristics of sound waves.
In Physics "Sound is a vibration that typically propagates as an audible wave of pressure, through a transmission medium such as a gas, liquid or solid".
Quick Facts: Humans can only hear sound waves as distinct pitches when the frequency lies between about 20 Hz and 20 kHz. Sound waves above 20 kHz are known as ultrasound and is not perceptible by humans. Sound waves below 20 Hz are known as infra sound. Different animal species have varying hearing ranges.

Characteristics of sound:

• Pitch or Frequency
• Loudness or intensity
• Quality

On the basis of thesecharacteristics, sound can be recognized as we recognize a person from his/her voice. Pitch refers to the rate of vibration of sound and is measured in Hertz(Hz). Loudness is measured in decibels (dB), a unit based on the weakest sound that can be detected by the human ear.
Phenomenon Related to sound:
Diffraction: Like light, sound waves spread as they move past an obstacle or through a narrow aperture. If the aperture is small, the sound waves spread out in all directions
Reflection: Deflection of sound waves into new directions by a surface is known as 'reflection of sound'.
Refraction: It is the change of direction of a sound wave on passing from one medium to another.
Echo: Repetition of sound by reflection is known as Echo.
Oscillation: Oscillation is the term used to describe anything that vibrates.
Sound waves and Music: Sound is generated by a vibrating system setting up waves in the surrounding air. Musical sounds are produced by a vibration with a definite pitch often produced by a vibrating string or a vibrating column of air in tube, which doesn't progress from one point to another but causes the string or column of air to vibrate as a whole with its characteristic frequency.
Ultrasonic and Supersonic Sounds: Sounds of frequency is higher than 20,000 Hz are calledultrasonic and are inaudible. The human ear is normally sensitive to sounds whose frequencies are between 16 and 20,000 Hz. The speed that is greater than the speed of sound is known as Supersonic. The speed of aeroplanes travelling at supersonic speeds is measured in Mach numbers. The sound waves of frequency lower than 16 Hz are called infrasonic.
Speeds of sound in different media:

Speed of sound: The Speeds of sound depends upon the nature of the carrier media. Sound doesn't travel through vaccum and has maximum speed in solid. In general the speed of sound refers to the speed at which sound travels to the speed at which sound travels in air at sea level. In dry sir at 0[latex]{^oC}[/latex], the speed of sound is about 331 m/s or 750 miles/hour. The presence of water vapors in the air increases the speed of sound slightly.
Broadcasting Radio waves: AM radio waves are usually measured in kilohertz(kHz), while FM radio waves radio waves are measured in megahertz(MHz). A Station at960 Hz on the AM radio broadcasts radio waves that have a frequency of 960,000 vibrations per seconds. A station at 101.7 MHz on the on the FM radio broadcasts radio waves with a frequency of 101,700,000 Hz.
Anti-noise Technology: Destructive sound interference is at the heart of the anti-noise technology. such noisy devices as jackhammers are being equipped with microphones that send the sound of the device to electronic microchip, which creates mirror-image wave patterns of the sound signals. Anti-noise devices are becoming more common in aircraft, which today are much quitter inside than before this technology was introduced.

1. The source of the sound is always the____?

A. Vibration of an object B. Transmitter of the object C. Pressure of the speaker D. Waves of an object

Answer: Option A
2. The speed is maximum in ____?

A. Solid B. Liquid C. Gas D. Same in all cases

Answer: Option A
3. The pitch of the sound depends on

A. Amplitude B. Frequency C. Wavelength D. Velocity

Answer: Option C
4. Sound waves do not travel in ____

A. Violet light B. Green light C. Red light D. Yellow light

Answer: Option A
5. What is the speed of the sound in Glass

A. 5200 - 6000 m/s B. 5000 - 6000 m/s C. 5000 - 6200 m/s D. 3000 - 5000 m/s

Answer: Option B
6. Sounds of frequency is higher than 20,000 Hz are called ___

A. Ultrasonic B. Supersonic C. Wave D. Music

Answer: Option A