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# What is sound?

Physics | 7-14 yrs | Interactive

## What is sound in physics?

Sound is a longitudinal, mechanical wave. It is caused by the back and forth vibration of the particles of the medium through which the sound wave is moving. The vibrations of the object set particles in the surrounding medium in vibrational motion, causing the auditory receptors to detect them. This is called sound.

## Does sound need a medium to travel?

Yes, sound needs a medium to travel. It can travel through any medium, but it cannot travel through a vacuum. Sound is absent in outer space, as there is no medium to carry sound vibrations.

When the vibrations are fast, you hear a high note, and when the vibrations are slow, it creates a low note.

## What are the components of a sound wave?

Wavelength – A sound wave is created due to pressure variations caused by vibrations. There are low pressure areas and high pressure areas. The high pressure areas are represented as crests and low pressure areas as troughs.

The physical distance between two consecutive crests or troughs in a sound wave is referred to as a wavelength.

Amplitude – In sound waves, amplitude refers to the magnitude of compression or expansion experienced by the medium the sound wave is travelling through.

High amplitude means loud noise. Low amplitude means low sound.

Pitch – Pitch/Frequency in a sound wave refers to the rate of the vibration of a particular sound travelling through air. It is calculated in cycles per second. The SI Unit for Frequency is Hertz.

The speed or velocity is calculated as frequency multiplied by wavelength.

Velocity of Sound = Frequency X Wavelength

## What are the types of sound?

There are two types of sound, Audible and Inaudible.

• Inaudible sounds are sounds that the human ear cannot detect. The human ear hears frequencies between 20 Hz and 20 KHz.
• Sounds that are below 20 Hz frequency are called Infrasonic Sounds. Elephants use Infrasonic sounds to communicate with herds 100s of kms away.
• Sounds that are above 20 KHz frequency are called Ultrasonic Sounds. Dogs, Bats can hear high frequency sounds.

## 6 Interesting facts about sound

1. Sounds travel at 340.29 m/second at sea level and 20 degrees celsius.
2. Sounds that are higher in frequency than audible sounds are known as ultrasonic sounds. Bats, whales, dolphins, dogs use ultra sound for echo location (to find either their location or to find or locate food, prey, or enemies and danger) and navigation.
3. A cat can hear high frequency sounds two octaves higher than humans.
4. Elephant communicate in sound waves in lower frequencies that human ears cannot detect.
5. The study of sound waves is called acoustics.
6. Flies are unable to hear any sounds.
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