Unit 2 · Light, Sound & Information · Week 1

What is actually moving when a wave travels?

A pebble drops in a pond and ripples spread outward — but a leaf floating on the water only bobs up and down. What is actually traveling, and what is staying in place?

SEP: Using Mathematics & Computational Thinking · Developing & Using Models DCI: PS4.A Wave Properties CCC: Patterns · Energy & Matter

NGSS MS-PS4-1 ~50 minutes Learner code: —

Make this lesson work for you:

Start here

How we work this lesson (our expectations)

Bring your curiosity — the puzzle comes first
Use what you see as evidence
Slower thinking beats faster guessing
Every support is for everyone — open any that helps

30-second check-in self-awareness

Before we look at the pond, check in with yourself: on a scale of 1 (really scattered) to 5 (locked in), where is your focus right now? If you're at a 1 or 2, that's fine — the steps below are designed to pull you in gradually. Try one slow breath and move to the Do-Now.

Do-Now Quick recall

No looking back — this is about what's already in your head. Writing, not perfection, is the goal.

From Unit 1: what does the word energy mean to you, in one sentence?
Think about a sound you hear every day (a voice, a car, a bell). Something must be moving to make that sound reach your ears. What do you think is moving?
When you drop a stone in a puddle, what shape do the ripples make? Sketch or describe it in words.

The phenomenon

Pond ripples spread outward after a pebble is dropped, but the leaf only bobs — it does not travel to shore.

Imagine you are standing by a still pond. You drop a pebble and watch perfect rings spread outward in every direction — moving, growing, reaching the shore. But look at a leaf floating nearby. The leaf does not drift to shore. It rises and falls, rises and falls — and stays almost exactly where it was. If the ripples are moving, how can the leaf be staying put? Something is traveling across that pond, but it is not the water. Our question: what is actually moving when a wave travels?

Notice & Wonder. Write one thing you notice in the image and one thing you wonder. Hold onto your wonder — you will answer it today.

Build it Three big ideas, one step at a time

Each step builds on the last. There is a quick check at the end before you practice on your own.

Step 1 — A wave is a disturbance that carries energy, not matter

When the pebble hits the pond, it pushes the water up. That water pushes the water next to it up, which pushes the next bit, and so on — like a domino chain of bumps. What travels outward is the disturbance — the bump itself. The water molecules (matter) mostly stay in place; they just pass the bump along. This is what a wave is: energy transferred through a medium without a net movement of matter. The leaf tells you this directly — it bobs, but it does not travel.

This is also true of a plucked guitar string: the string vibrates in place, but the sound energy travels outward through the air to reach your ears.

Step 2 — Parts of a wave: amplitude, wavelength, frequency

Scientists describe waves with three measurable quantities. Amplitude is the height of the wave above the rest position — how far the medium is pushed up (or down) from normal. Wavelength is the distance from one peak to the next peak (or one trough to the next trough). Frequency is how many peaks pass a fixed point each second, measured in hertz (Hz). These three numbers, together, give a complete mathematical picture of a wave.

A transverse wave. Amplitude (red) = height from rest line to peak. Wavelength (green) = distance between two peaks.

Step 3 — Bigger amplitude = more energy

Here is where math and models connect: amplitude is related to the energy carried by a wave. Double the amplitude — push the water twice as high — and the wave carries significantly more energy. A tiny ripple from a pebble barely rocks the leaf. A huge ocean wave from a storm carries enough energy to knock you off your feet. Same connection for sound: a loud sound (high amplitude) carries more energy than a whisper (low amplitude). For light: bright light (high amplitude) carries more energy than dim light. This is why MS-PS4-1 asks you to use a mathematical representation — comparing amplitudes lets you compare energies, even without equations.

Energy & Matter connection (Unit 1 link): Energy is not created by the wave — the pebble or the guitar string had kinetic energy first. The wave transfers that energy outward, conserving it, without moving the matter along with it. The same "energy transfers but is not created" rule from Unit 1 applies here.

Worked example — label a wave and reason from amplitude to energy

Wave A has an amplitude of 4 cm. Wave B has an amplitude of 8 cm. Both waves have the same wavelength and frequency.

Expert reasoning step by step:
1. Amplitude is the height from the rest position to the peak.
2. Wave B's amplitude (8 cm) is twice Wave A's amplitude (4 cm).
3. Because amplitude is related to energy, Wave B carries more energy than Wave A.
4. If both waves are water waves, the leaf would bob higher in Wave B — and higher bobbing takes more energy to produce.
Conclusion: Wave B carries more energy. The matter (water) is displaced more, but it still returns to its rest position — it does not travel with the wave.

Show the comparison as a diagram Tier 2 · visual

Draw two sine waves side by side on the same rest line. Make Wave A short and flat (small amplitude). Make Wave B tall and steep (large amplitude). Label the amplitude on each with a vertical arrow from the rest line to the peak. Under each, write: "carries less energy" (A) and "carries more energy" (B).

Notice: the wavelength (distance between peaks) is the same for both. Only the height changes — and the height determines the energy.

Your turn CER — what travels, what doesn't?

Use a Claim–Evidence–Reasoning model to answer the question below. Choose how you respond — all are equally valid.

✍️ Write it 🎨 Draw + annotate the pond scene 🗣️ Say it out loud (record yourself)

The task: When a wave moves across the pond, what travels — the energy or the water (matter)? Make a claim, give evidence from the leaf observation, and explain your reasoning using the ideas of energy and matter.

I want sentence starters Tier 2 · frames

Claim: When a wave moves across the pond, the ________ travels, but the ________ does not.

Evidence: I know this because the leaf ________ instead of drifting toward shore, which shows that the water ________.

Reasoning: This makes sense because a wave is a disturbance that transfers ________, and the matter only ________ in place to pass the disturbance along.

Word bank: energy · matter · bobs up and down · stays in place · travels · wave · amplitude · disturbance

Let's make it concrete first Tier 3 · re-teach

Analogy — The stadium wave: At a sports game, fans do "the wave." Each person stands up and sits down in turn — the wave travels all the way around the stadium, but each person stays in their seat. No one moves to a new seat. The "wave" (the moving disturbance) traveled; the fans (matter) did not. A water wave works exactly the same way: each water molecule goes up and down, but the wave travels outward.

Fill in: In the pond, the ________ traveled from the pebble to the shore, but each water molecule only ________ up and down in place. We can tell because the leaf ________.

Say your answer aloud once, then write it. One sentence per CER part is enough.

Push my thinking Extension

Earthquakes create seismic waves that travel through solid rock — and geologists use the amplitude of those waves to estimate how much energy was released. Using what you know about amplitude and energy, explain: why would a magnitude-7 earthquake (much larger amplitude seismic wave) cause so much more damage than a magnitude-4 earthquake? Then design one investigation you could do in the classroom to test how amplitude relates to energy using a rope or a slinky.

Check yourself Did it click?

Success criteria — I can:

explain that a wave transfers energy without transferring matter (the leaf bobs, it doesn't travel);
define amplitude, wavelength, and frequency using a labeled diagram;
use amplitude to compare the energy of two waves.

When a wave moves across the pond, which of the following best describes what is happening?

Re-teach: energy travels, matter stays Tier 3

A wave is a disturbance passing through a medium (like water). Each part of the medium moves a little — up then down — and then passes the disturbance to its neighbor. The disturbance (carrying energy) moves forward. The medium (matter) does not.

Think of the stadium wave analogy: fans stand up and sit down one after another — the "wave" travels around the stadium, but every fan stays in their seat. Same thing in the pond: the wave (energy) travels to shore; the water molecules stay put and just pass the motion along.

Try answering choice B again with this in mind: what is the "disturbance" in the pond — and what is staying in place?

Reflect, then show what you know

Reflection responsible decision-making + metacognition

Think about a moment in this lesson where you had to change your thinking — maybe you expected the water to move to shore, or you weren't sure what amplitude meant. What made you revise your idea? Noticing when you update your thinking is exactly what scientists do.

Exit ticket — answer on paper or in your notebook.

New In your own words: when a wave travels, what moves — the energy or the matter? How does the leaf in the pond prove your answer?
New Wave X has an amplitude of 3 cm. Wave Y has an amplitude of 9 cm. Which wave carries more energy, and how do you know?
Spiral In Unit 1 you learned that energy is never created from nothing — it transfers from place to place. How does the pebble-in-the-pond wave fit that idea? Where did the wave's energy come from originally?
Spiral In Unit 1 you described matter as moving particles. How does that particle idea connect to what happens when a water wave passes — what are the water's particles actually doing?
Transfer Preview: Next week we'll explore what happens when a light wave hits a mirror versus a window. Predict — what might be different about where the energy goes in each case?

Educator panel — facilitation, accommodations, answer key

At a glance

Standard: NGSS MS-PS4-1 — use mathematical representations to describe a simple model for waves that includes how amplitude is related to energy. 3D: SEP Using Mathematics & Computational Thinking + Developing & Using Models · DCI PS4.A Wave Properties · CCC Patterns + Energy & Matter. Unit throughline: energy transfers without being created (Unit 1 conservation law) — now in the specific form of wave propagation. This lesson is the conceptual foundation for the rest of Unit 2 (reflection, refraction, absorption in Week 2; sound + communication in Week 3+).

Materials (fully digital-capable): student notebook; optional physical: a long rope or slinky to demonstrate a transverse wave, a bowl of water and a floating object for the phenomenon. No lab required.

Facilitation arc (Rosenshine)

Launch phenomenon with the SVG diagram — do not define wave yet. Let students notice the leaf and wonder (3 min).
Do-Now retrieval while you take attendance; listen for "energy" from Unit 1 — affirm those connections (3 min).
Build Steps 1–3 with worked example; pause after Step 1 to check "matter vs energy" before moving to wave parts (14 min).
Differentiated CER practice — circulate and ask: "What's your evidence?" Listen for leaf observation being used (15 min).
Self-check branching: students who choose A or C route to the re-teach panel; you may read it aloud or pair-share (5 min).
Brain break → reflection → exit ticket. Collect exit tickets #3 and #4 as formative data for Unit 1 retention (10 min).

Common misconceptions to anticipate

"The water moves to shore." Address by focusing on the leaf: "Does the leaf end up at shore by the end?" Students who believe this will choose distractor A in the self-check.
"Amplitude = volume/brightness." Partially correct — these are the observable correlates. The scientific point is that amplitude is a geometric/mathematical property (height) that is directly related to energy. Keep the two ideas connected, not separated.
"Bigger wave = faster wave." Speed and amplitude are independent properties. Speed depends on the medium, not amplitude. Do not address this yet — it comes in Week 3 (sound speed) — but flag it if it arises.

IEP / 504 accommodation cards

Common accommodations mapped to this lesson

Accommodation	How it is already built in / what to do
Text read aloud	Every passage has a Listen button (Web Speech TTS); simplified toggle shortens all text.
Reduced reading load	"Reading: Simplified" swaps all passages to plain-language, shorter versions throughout.
Chunking / extended time	Three clearly labeled steps with visual breaks; progress auto-saves to localStorage — students can stop and resume.
Sentence frames / word bank	Tier-2 panel under the CER task provides both frames and an 8-word bank.
Concrete analogy / model	Tier-3 panel uses the stadium wave analogy and a cloze-fill sentence. Optionally use a physical rope or slinky.
Alternative response mode	Students may write, draw and annotate, or speak their CER aloud — all stated as equally valid.
Behavior / focus (504, ADHD)	Named expectations (PBIS), 30-sec check-in, built-in brain break with physical movement.
Multilingual / English learner	Simplified text, SVG visuals carry the full meaning, sentence frames, word bank in the Tier-2 panel, and home-language reflection is explicitly allowed.

Exit ticket answer key

Energy moves; matter (water) stays in place. Evidence: the leaf bobs up and down but does not drift toward shore — the water molecules move up and down without traveling outward.
Wave Y (9 cm amplitude) carries more energy. Amplitude is related to energy — a taller wave displaces the medium more and requires more energy to produce.
The wave's energy came from the kinetic energy of the falling pebble. When the pebble hit the water, that kinetic energy was transferred to the water as wave energy and then spread outward. Energy was not created — it was transferred (conserved, changing form).
When the wave passes, each water particle is briefly pushed up and then returns to its rest position. The particles oscillate (vibrate) around their original location — they do not permanently move outward. This is consistent with the Unit 1 idea that particles are always moving but can stay arranged in a pattern.
Open-ended prediction; credit any reasonable reasoning. Expected range: a mirror might bounce (reflect) the light energy back; a window lets the energy pass through (transmit). Both are reasonable previews of Week 2's reflection/transmission/absorption framework.

Why it is designed this way

Phenomenon-first with a surprising detail (leaf stays put) creates cognitive dissonance that drives genuine inquiry (NRC 2012; Reiser et al. 2021). The worked example explicitly models expert reasoning before students practice alone — fading support from model to guided to independent (Sweller 1988; van Merriënboer & Sweller 2005). The three-tiered support structure lets every learner access the same goal at the appropriate level of scaffolding (UDL 3.0; Fuchs & Fuchs 2017). The Do-Now and exit-ticket spiral items link explicitly to Unit 1 energy and matter concepts, making the energy-and-matter throughline visible to students and building interleaved retrieval strength (Roediger & Karpicke 2006; Rohrer 2012). The branching self-check transforms assessment into a next-step resource rather than a grade (Black & Wiliam 1998). The stadium-wave analogy in Tier 3 draws on an experience accessible to a wide range of cultural backgrounds and avoids assuming beach or ocean exposure (Gay 2018; Hammond 2015). The transfer exit-ticket item (predict reflection vs. transmission) previews Week 2 without requiring prior knowledge, giving every student a low-stakes starting point for the next lesson.