Physics
Physics
Problem
Explain, with reference to the speed of sound, why the minimum distance required to hear a distinct echo is smaller when the reflecting surface is under water than when it is in air.Intuitive explanation
The key is that sound travels much faster in water ( 1500 m/s) than in air ( 340 m/s). For an echo to sound distinct, your ear needs enough time between the original sound and its reflection—roughly 0.1 seconds. Since distance equals speed times time, a slower speed in air requires a larger distance to achieve that time delay, while the faster speed in water achieves the same delay over a smaller distance. So underwater echoes become distinct at closer range.
Intuitive explanation
The key is that sound travels much faster in water ( 1500 m/s) than in air ( 340 m/s). For an echo to sound distinct, your ear needs enough time between the original sound and its reflection—roughly 0.1 seconds. Since distance equals speed times time, a slower speed in air requires a larger distance to achieve that time delay, while the faster speed in water achieves the same delay over a smaller distance. So underwater echoes become distinct at closer range.