How can you say that the sound is a form of energy?

Explanation

1) Take a tin can and remove both ends to make a hollow cylinder.
2) Take a balloon and stretch it over the can.
3) Wrap a rubber band around the balloon.
4) Take a small mirror and stick it on the balloon.
5) Take a laser light and let it fall on the mirror.
6) After reflection the light spot is seen on the wall.
7) Now shout directly into the open end of the can and observe the dancing light.
Observations :
1) When sound is made, the energy produced from the sound vibrates the membrane of the balloon, resulting in the dancing of light ray.
2) This shows that sound is a form of energy which travels in air.
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