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Ping the water and listen. How long until the rock answers?
Sonar & Echolocation lab · Last updated: 16 October 2026
A boat sends a ping of sound down through the water and listens. A moment later an echo comes back from a rock below. You time the echo and work out how far away the rock is, just as ships and dolphins do.
What you'll discover
- Sound bounces off objects and comes back as an echo.
- Timing the echo, and knowing the speed of sound, tells you how far away the object is.
- The sound travels there and back, so the distance is half of speed times time.
The science in plain words
Sonar stands for sound navigation and ranging. A ship's sonar sends a short burst of sound, often ultrasound too high for humans to hear, into the water. When the sound hits the seabed, a shoal of fish or a rock, part of it reflects back as an echo, and a receiver on the ship picks it up.
Sound travels through sea water at about 1,500 metres per second, more than four times faster than in air. If the echo returns after 2 seconds, the sound has travelled 3,000 metres in total. But that is there and back, so the rock is 1,500 metres away. The rule is: distance equals speed times time, divided by two.
Bats and dolphins use the same idea, called echolocation. They make clicks or squeaks and listen to the echoes to find food and avoid obstacles, even in darkness or murky water.
Doctors use ultrasound echoes to see babies before birth, and scientists have mapped much of the ocean floor using sonar from ships.
Where it fits
- India, NCERT: Class 9 science, Chapter 11: Sound
- United States: Grades 6 to 8
- Next Generation Science Standards: MS-PS4-2
Common questions
How does sonar work?
A ship sends out a pulse of sound and times how long its echo takes to return. Knowing the speed of sound in water, it calculates the distance to the object, remembering to halve the round trip.
How do bats and dolphins use echolocation?
They make high-pitched clicks or calls and listen to the echoes. The time and direction of the echoes tell them where food and obstacles are, even in the dark.
Why does sound travel faster in water than in air?
Water molecules are packed much more closely and push on each other strongly, so vibrations pass along more quickly. Sound moves about four times faster in sea water than in air.
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Try it yourself
The Sonar & Echolocation lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.