Question

Take a plastic or tin can or a plastic glass. Remove its bottom. Stretch a piece of rubber balloon across one end and fix it with a rubber band. Put a few grains of say ragi or bajra on the stretched rubber. Now ask your friend to shout 'Hoorrey..... Hoorrey.....' from the open end of the glass. Observe the dancing of the grains up and down. Discuss the reason behind this.

Answer 1

Steps to Perform the Activity:

1. Prepare the Setup:

   • Remove the bottom of the can or glass.
   • Cut a piece of rubber balloon large enough to cover one open end of the can or glass.
   • Stretch the balloon tightly over the open end and secure it with a rubber band to ensure it is taut.

2. Add the Grains:

   • Sprinkle a few grains (ragi or bajra) on the stretched balloon surface.

3. Shouting into the Open End:

   • Ask your friend to shout "Hoorrey..... Hoorrey....." loudly into the open end of the can or glass.

4. Observe the Grains:

   • Notice how the grains "dance" by jumping up and down on the surface of the stretched balloon.

Observations: The grains jump and move up and down on the balloon when your friend shouts into the can/glass.

Explanation:

1. Sound as Vibrations:

   • When your friend shouts, their voice produces sound waves, which are vibrations in the air.
   • These sound waves travel through the air and strike the stretched balloon surface.

2. Balloon as a Vibrating Surface:

   • The balloon vibrates when sound waves hit it.
   • These vibrations are transferred to the grains on the balloon, causing them to "dance."

3. Effect of Loudness:

   • The louder the sound, the stronger the vibrations, and the higher the grains jump.

4. Why It Happens:

   • The grains act as tiny objects that visibly respond to the vibrations of the balloon, demonstrating how sound is a form of energy that travels through vibrations.