Sound class 9 physics

Jaya: Arvind! We hear many different kinds of sounds all day.

Arvind: Yes. Jaya. We can hear human voice- talking, laughing, crying, singing, traffic noise, sounds made by

animals, and also the musical sound.

SOUND

Jaya: So, Arvind how sound is produced?

Arvind: Jaya, sounds are produced due to the vibrations of a body or an object.

Jaya: Arvind, should we discuss it in detail with our teacher?

Arvind: Sure.

After completing the lesson, we will be able to:

Explain propagation of sound.

Explain transmission of sound in a medium.

Discuss speed of sound in solid, liquid and gases.

List out the characteristics of a sound.

Discuss and describe Doppler Effect in sound.

Illustrate Reflection of Sound.

Teacher (30 yr old): Good morning children.

Students (collectively): Good morning teacher.

Jaya: Mam! What is sound and how is it produced?

Teacher: It is simply the vibrations of air molecules. Here we perform some activities to understand this.

As you speak, place a finger lightly on your throat. You will easily feel the movement in your throat.

Now place your hand over the speaker of a transistor radio. Your hand will feel some vibrations.

Thus, vibration of a source is necessary for sound to be produced.

When the strings of a sitar are plucked, we hear musical notes.

When the stretched membrane of tabla or drum is struck, it vibrates and we hear its characteristic sound.

In case of a bell, a loud sound is produced due to its outer layer. When the bob at the center strikes the inner layer, it

starts vibrating and hence producing a sound.

Teacher, how is sound produced in a flute?

Good query Arvind. When we blow air into one end of a flute, air molecules in the flute vibrates and sound is

produced.