Why does the sound of water change as a bucket is filling from empty to full?
If you keep an empty bucket under the faucet and fill it with water, you can hear a loud sound at first, but the sound gets louder as the bucket fills up.
Answer: When an empty bucket is placed under the tap and filled with water, the vibration of the air inside the bucket produces a sound. Since the length of the air column in an empty bucket is longer, the frequency of the sound produced is lower. That’s why the sound is thick.
But as water fills the bucket, the length of the vibrating column of air inside it decreases. As a result, the frequency of the generated sound, i.e. the sharpness of the sound increases. That’s why as the bucket gets filled, the sound gets louder.