Lesson 8 of 8 · Waves
The Doppler Effect
🌊
🎯 Your mission
Set it up. Test it. Be amazed.
⚡ The twist
Nature loves to surprise the careful watcher.
What you'll learn
When a source moves towards you, each wave is emitted a little closer than the last, so the wavelength you receive is shortened and the pitch rises. Moving away, it lengthens and the pitch falls. Astronomers use the same effect as redshift to measure how galaxies move.
Key words
Doppler effect
The change in observed frequency when source and observer move relative to each other.
redshift
The stretching of light to longer wavelengths from a source moving away.
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
- phone with spectrum analyser app
- safe viewpoint well back from a road
Get ready
⚠️ Safety first
- Stay well behind a barrier or fence — never stand at the roadside.
- Go with an adult.
Step 1 of 4 · Read
Think about what you just learned: say what "Doppler effect" and "redshift" mean in your own words before you start.
Step 2 of 4 · Do
Stand safely back from a road and record a passing vehicle's siren or engine on your phone. Analyse the recording with a spectrum app and measure the frequency before and after it passes.
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 2
Question 2 of 2
Mind = blown
🔬 The more you look, the more nature shows you.
Nice work!
You got 0 of 2 right.
Next Smart Experiment
We'll pick an experiment that matches exactly how you're thinking right now.
✨ 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?
The Doppler Effect
Set it up. Test it. Be amazed.
Full screen — no distractions
Done with science? Try something else
Print the whole Waves track
All 9th Grade Waves lessons as a printable PDF, with worksheets and answer keys.