Science Puzzle
The Echo Reflection
You stand facing a large cliff and shout. Exactly 2 seconds later you hear the echo. Sound travels at 343 metres per second in air.
How far away is the cliff?
The Answer
343 metres. The sound had to travel to the cliff and back, so the total distance covered was 343 m/s × 2 seconds = 686 metres. That 686 metres is the round trip, so the cliff is half of that: 343 metres away.
This is the principle behind sonar and echolocation. Bats emit ultrasonic pulses and time the returning echo to determine the distance of objects with remarkable precision. Ships use the same principle to measure ocean depth (sonar), and ultrasound medical imaging uses it to map internal structures.
The key step that most people miss is remembering to halve the total distance: the echo time is for the round trip, not a one-way journey.
The principle: Acoustic reflection and echolocation. Sound travels to a reflective surface and back. Dividing the total travel time by two and multiplying by the speed of sound gives the one-way distance.