How to play Echo Sounder
- Choose a test and read the speed, the times, or the distances on the card.
- Use d = v·t ÷ 2, t = 2d ÷ v, and v = 2d ÷ t. An echo always travels the distance twice.
- Type your prediction and press Start. The sound goes out and comes back in slow motion.
- Compare the orange dashed lines with the echoes on the right, or the orange line with the seabed, the fish, or the moth.
Echoes and reflection
When a wave reaches the edge of what it travels through, part of it bounces back: it is reflected. For sound, the reflection is an echo. A clap in a canyon, a bat's squeak hitting a moth, and a ship's sonar ping hitting the seabed all come back after a delay, and that delay measures distance: the sound covers the way out and the way back, so d = v·t ÷ 2. The speed depends on what the sound travels through, about 340 m/s in air and 1500 m/s in sea water. Echo sounders on ships ping many times a second to draw the shape of the seabed and spot shoals of fish, which return weaker echoes earlier. Bats and dolphins do the same by instinct, using echo delays of thousandths of a second to hunt in the dark. Doctors use ultrasound echoes inside the body, and the same idea with radio waves is radar.
A focused learning model
The sound travels at a constant speed in straight lines and reflects perfectly; the source and receiver stay still and are in the same place. The pulse is drawn as spreading circles and the echo as circles spreading back. The recording shows the ping and each echo as short bursts, weaker from the fish. Time runs slower than real time by the factor shown, so each run lasts 4 s and ends as the last echo returns; the clock shows the real time in milliseconds. Answers within 2% are right.