Sound (part -1) class 8

SOUND

Q.1. What is sound?

Ans. Sound is a form of energy, a sensation felt by our ears and makes us able to hear something. We hear many sounds around us like: sounds of talking, chirping of birds, ringing of bell, fluttering of clothes, machines etc.

Q.2. What is the cause of sound?

Ans. Vibration in an object produces sound. To and fro or back and forth motion of an object is called vibration. The energy required to make an object vibrate and produce sound is provided by some outside sources (like our hands, wind etc.). For example:

  • We can feel vibrations by keeping our hand on our throat while speaking where vocal cords vibrate to produce sound.
  • The sound of a ‘Dholak or tabla’ is produced by the vibrations of its stretched membrane on strucking.

Q.3. Tabulate the Musical Instruments and their Vibrating Parts which vibrate to produce sound.

Ans.

S.No.

Vibrating Part of Instrument Producing Sound

Examples

1.

Stretched membrane

Drum, Tabla, Dholak, Mridangam

2.

Stretched string

Sitar, Violin, Guitar, Harp

3.

Air –column

Flute, Harmonium, Mouth-organ, trumpet

4.

Plate type

Cymbal, kartal, Ghatam, Metal bell

Q.4. How do humans produce sound?

Ans. In humans, the sound is produced by the voice box or the larynx. It is at the upper end of the windpipe. Two vocal cords are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air.

While speaking, the vocal cords come close to each other. When the lungs force air through the slit, the vocal cords vibrate, producing sound. Muscles attached to the vocal cords can make the cords tight or loose. When the vocal cords are tight and thin, the type or quality of voice is different from that when they are loose and thick.

The vocal cords in men are about 20 mm long. In women these are about 5 mm shorter. Children have very short vocal cords.

                               

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