Sound Class 9 CBSE Notes - Chapter 12

There are various sources of sounds around us – from the birds, the leaves rustling in the wind to the cars and the sounds of our own voice. In science, we define sound as a form of energy that travels in waves. A body produces soundwaves and these vibrations cause the medium around the object to vibrate. We pick up these vibrations as audible cues.

Propagation of Sound

We can hear the sounds around us because it travels through various mediums which helps it propagate. These mediums contain atoms which vibrate when a body produces sound. However, once we cross the earth’s atmosphere and into outer space, we cannot hear any sound because space is a vacuum.

This essentially confirms the fact that sound needs a medium to travel. Sound even travels in water, and it travels nearly four times as fast as air. This is due to the fact that the molecules are more closely packed in water than in air.

Sound Class 9 Notes – Questions

  1. How do you define sound in science?
  2. Does sound travel in water?
  3. Why doesn’t sound travel in a vacuum?
  4. Can sound be reflected off a solid surface?
  5. What is meant by reverberation?

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Practise This Question

Crop variety improvement is done to achieve which of the following objectives?