Video narration
Subah school ki ghanti bajti hai - tannn! Aap sunte hue kaksha mein ja rahe hain. Dhatu aage-peeche hilti hai. Is hilne ko kampan kehte hain; yahi dhvani paida karti hai. Lekin awaaz ghanti se hawa mein udkar kaan tak nahin jaati. Hawa ke kan ghanti se aapke kaan tak nahin aate; har kan apne paas ke kanon ko hilakar halchal aage badhata hai. Yeh halchal hawa jaise madhyam - dhvani pahunchane wali cheez - se aage badhti hai. Jab yeh aapke kaan tak pahunchti hai, aap ghanti ki awaaz sunte hain. Hawa na ho to kya hoga? Nirvaat, yani hawa ya doosre padarth se khaali jagah, mein dhvani nahin phailti; aage kampan pahunchane ka madhyam nahin hota. Agli baar school ki ghanti baje, yaad rakhein: uske kampan ko aapke kaan tak pahunchne ke liye hawa jaisa madhyam chahiye.