My family lives on the second floor. One Sunday morning, I just woke up and suddenly found the voice of my grandfather on the first floor echoing in my ear, as if he were beside me! I quickly got up, and grandpa's voice immediately dropped a lot! It turns out that he is doing morning exercises in the yard! I put my ear on the pillow again, and grandpa's voice became clear again! That's weird. Why?

It suddenly occurred to me that science class said that sound can spread in gas, solid and liquid, and it spreads fastest in solid. Have I discovered the secret of sound transmission? I quickly got up and took out a "earth phone" made of paper cups. I threw one end of the earth phone to grandpa from the window and asked him to help me find the answer. Grandpa readily agreed. However, when we picked up the paper cups at the same time, Grandpa's voice didn't come from the paper cups. What's going on here? Originally, I found that the thin thread connecting the paper cups was not tightened. I quickly asked grandpa to step back and tighten the thread. Suddenly, grandpa's voice came out of the paper cup clearly, just like he whispered in my ear!

I finally understood the secret of sound transmission through experiments! Sound travels through vibration. When the thin thread of the "earth phone" is not tightened, the sound propagates in the air. When the thin thread is tightened, the sound propagates directly through the thin thread, which is of course very clear! Therefore, sound travels fastest in solids. Grandpa's voice I heard at the pillow in the morning also reached my ears directly through the window, floor and bedstead, just like talking around!