Question

Standing at a distance, how is it possible to detect the filling of bucket under a water tap by hearing the sound? 

Answer 1

As the bucket fills up, the air column or amount of air inside the bucket decreases. So as a result, the pitch or shrillness of the sound will increase, as frequency or pitch of the sound is inversely proportional to the length of the vibrating air column. Also, the amplitude or the loudness of the sound will decrease, as the amount of the air column vibrating decreases as the bucket fills up. So with the increase in the shrillness of the sound, you can detect the filling up of the bucket. So the more the shrillness, the more the bucket has been filled. When the bucket overflows, the shrill sound will be heard no more.