Lesson 6 of 8 · Waves
Echo Location: Timing a Pulse Gives Distance
🌊
🎯 Your mission
Set it up. Test it. Be amazed.
⚡ The twist
Nature loves to surprise the careful watcher.
What you'll learn
Distance from a reflected pulse is d = v × t / 2, the halving accounting for the fact that the pulse made a round trip. A sonar ping returning after 0.4 s through water at 1,500 m/s means a seabed 300 m down. The detail such a system can resolve is set by the wavelength — nothing much smaller than one wavelength shows up — which is why medical scanners run at megahertz frequencies rather than at the kilohertz a ship's echo sounder uses.
Key words
echo sounding
Finding distance by timing how long a pulse takes to reflect from a surface and return.
ultrasound
Sound above about 20 kHz, whose short wavelength resolves fine detail and which does not ionise tissue.
Make a hypothesis first
Before you start: write down what you think will happen, and why.
Say your guess out loud — then find out if you were right.
Get ready
🧰 What you need
- stopwatch
- tape measure
- large flat wall
- notebook
⚠️ Safety first
- Choose an open outdoor space away from traffic.
Step 1 of 4 · Read
Think about what you just learned: say what "echo sounding" and "ultrasound" mean in your own words before you start.
Step 2 of 4 · Do
Stand a measured distance from a large flat wall, clap in time with the returning echo, and use a partner's stopwatch over 20 claps to find the interval. Calculate the speed of sound from d = v × t / 2 and compare it with 340 m/s.
Step 3 of 4 · Observe
Record what actually happened, including anything that did not match what you expected.
Step 4 of 4 · Record
Write a conclusion that answers the question this lesson opened with, and state your uncertainty.
Question 1 of 3
Question 2 of 3
Question 3 of 3
Mind = blown
🔬 The more you look, the more nature shows you.
Nice work!
You got 0 of 3 right.
Next Smart Experiment
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✨ More to explore
🌍 Where you see this in real life: This shows up in your everyday life more than you'd think.
🏆 Stretch challenge (try it this week): Try one experiment in real life this week — even a tiny one.
👨👩👧 For the dinner table: “What's the most surprising thing you learned today?”
Share this experiment
Send it to a parent who's looking for a 10-minute kitchen science win.
Ready?
Echo Location: Timing a Pulse Gives Distance
Set it up. Test it. Be amazed.
Full screen — no distractions
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Print the whole Waves track
All 8th Grade Waves lessons as a printable PDF, with worksheets and answer keys.