Explain how sound is produced by your school bell.

Solution:
When we hit a school bell by a hard gong, it moves back and forth about its equilibrium position. Thus, the edge of the bell strikes the particles in the air. When the edge moves forward, air particles are driven forward. This forward motion of the bell produces a region where the air pressure is slightly higher than average. This region is called compression. When the edge moves backward, air particles near it have more space and thus, they spread farther apart. This backward motion produces a region where the air pressure is slightly below average pressure. This region is called rarefraction. Collisions among the air particles cause the pressure variations to move away from the bell in all directions. If you were to focus at one spot, you would see the value of the air pressure rise and fall. In this way, the pressure variations i.e., the sound is produced by the bell which is transmitted through air (see fig.).