Unit 1 · Energy & Matter in My World · Week 3

Where does a melting popsicle GO?

You leave a popsicle on the counter. An hour later: a puddle. By afternoon: nothing at all. The popsicle vanished — or did it?

SEP: Developing & Using Models DCI: PS1.A Structure & Properties of Matter CCC: Energy & Matter (Conservation)

NGSS MS-PS1-4 ~50 minutes Learner code: —

Make this lesson work for you:

Start here

How we work this lesson (our expectations)

Follow the particles — they tell the real story
Use the model, not just the memory
Reasoning matters more than getting it right the first time
Supports are for everyone — open any you want

30-second check-in self-awareness

Before we start: think of a time something seemed to disappear — food left out, a wet sidewalk after rain, a puddle on a hot day. Did it actually vanish, or did it go somewhere you couldn't see? Hold that thought. Today's lesson is going to change how you see it. On a scale of 1 (foggy) to 5 (sharp), how is your focus? If you're at a 1 or 2, the Listen buttons can read every passage to you — use them.

Do-Now Quick recall

No looking back — let your memory work. Retrieval now makes the lesson stick better later.

Week 1 spiral What is heat, in terms of particles? (Hint: it's about how fast they move.)
Week 2 spiral When energy moves from a warm object to a cold one — which direction does it always travel? What is that direction called?
Ice is a solid. Water is a liquid. Steam is a gas. What do you think is different about the particles in each one?

The phenomenon

Three snapshots of the same water. The particles are the same in every panel — only their arrangement and speed change. Red arrows = thermal energy flowing in from the room.

On a hot afternoon you set a popsicle on the kitchen counter. Half an hour later there is a sticky puddle. By the time you come back after dinner, even the puddle is gone — the counter is dry and clean. Nothing is in the trash. No one cleaned it up. The popsicle seems to have completely disappeared. Where did it go? Was anything destroyed, or is the matter still out there somewhere?

Notice & Wonder. Write one thing you notice in the diagram above and one thing you wonder. We will answer your wonder today.

Build it Follow the particles, step by step

We will trace the popsicle's journey using what we know about particles. Each step builds on the last — check in before moving forward.

Step 1 — States of matter are particle arrangements

Matter can exist as a solid, a liquid, or a gas. The difference is not what the particles are — it is how they are arranged and how fast they are moving. In a solid, particles are locked tightly in a pattern; they vibrate in place. In a liquid, particles still touch but can slide past each other — no fixed shape. In a gas, particles have enough energy to break away from each other entirely, spreading out to fill any space. Same particles. Same matter. Different arrangements.

Step 2 — Thermal energy changes the arrangement

From Week 1: heat is particle motion. From Week 2: thermal energy travels from warm to cold. The warm room air transfers energy into the cold popsicle. As the popsicle's particles gain energy, they move faster — fast enough to break out of the locked solid arrangement and start sliding past each other. This is melting: solid → liquid. Keep adding energy and the liquid particles eventually move fast enough to escape into the air as a gas. This is evaporation: liquid → gas. Both changes are driven by thermal energy flowing in.

Step 3 — The matter is conserved: it is now water vapor

The popsicle's particles did not disappear. They are invisible to the eye, but they are in the air around you as water vapor — individual water particles mixed invisibly into the air. The amount of matter did not change at all. If you could capture all the air in a sealed jar right after the puddle dried, and then cool the jar back down, the same water would condense right back as liquid on the inside of the jar. This is the conservation of matter: the total amount of matter before and after a change stays the same. Matter is never destroyed; it only changes form or moves.

Worked example — a particle model of the popsicle's full journey (watch an expert reason through it)

Before: The solid popsicle has particles locked tightly together, vibrating slowly (low thermal energy). The room air particles nearby are moving faster (higher thermal energy).
Energy transfer begins (Week 2): Thermal energy moves from the warm room → into the cold popsicle. This is the endothermic direction: energy flows in.
Melting: The popsicle's particles gain enough energy to stop being locked. They begin sliding — solid → liquid. The puddle forms.
Evaporation: Room air keeps transferring energy in. Individual liquid particles near the surface gain enough energy to escape entirely — they fly off as gas (water vapor) one by one.
Conservation check: Every particle that was in the popsicle is still somewhere in the room. If you sealed the room and cooled it back down, all the water vapor would condense back into liquid — same amount. Matter was rearranged, never destroyed.

Show the particle model as a diagram I can draw Tier 2 · visual

Draw three boxes left-to-right with arrows between them:

Box 1: small circles packed tightly, labeled "SOLID — particles locked, low energy."
→ thermal energy in →
Box 2: same circles loosely spaced, sliding, labeled "LIQUID — particles sliding, more energy."
→ thermal energy in →
Box 3: same circles very far apart and spread across the page, labeled "GAS (vapor) — particles free, high energy."

Under all three boxes, write: Same number of particles throughout. Matter is conserved.

Your turn Where did the puddle go?

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

✍️ Write a CER paragraph 🎨 Draw + label a particle model 🗣️ Explain it out loud or record yourself

The task: The popsicle puddle evaporated. Is the water gone? Make a claim (yes/no and what happened), give evidence from the particle model, and explain your reasoning using conservation of matter and thermal energy.

I want sentence starters and a word bank Tier 2 · frames

Claim: The water is not gone — it is now ________.

Evidence: I know this because when thermal energy was added to the liquid, the particles ________, allowing them to escape into the air as ________.

Reasoning: This shows conservation of matter because the same ________ are still in the room — they just changed from ________ to ________. Matter was not ________; it was ________.

Word bank: particles · water vapor · evaporated · thermal energy · liquid · gas · destroyed · rearranged · conserved · solid · state of matter

Let's build it with a simpler analogy first Tier 3 · re-teach

Analogy — the "people in a gym" version: Imagine 100 students packed shoulder-to-shoulder in a gym (solid). The coach yells "spread out" and they all walk to give each other space (liquid). Then the coach says "go wherever in the building you want" and they scatter through every hallway and room (gas). You can't see all 100 students anymore — they're spread all over the building. But how many students are there? Still 100. No student disappeared.

That is what happens to water particles. They spread out into the air. You can't see them — but they are still there.

Fill in: The water particles are not gone — they are now in the ______ as ______. The total number of particles is the same because matter is ________.

Now say your answer out loud once, then write it in one or two sentences.

Push my thinking — conservation test design Extension

Design a procedure to prove conservation of matter during evaporation using only a scale, a sealed container, and a popsicle. What would you measure, and what would you predict you'd find? Then consider: if you did the same test in an open container, what would happen to the mass reading? Why?

Bonus: water vapor is invisible, but you can measure it indirectly. How might a sealed bag on a scale before vs. after the popsicle melted help you make the case for conservation of matter?

Check yourself Did it click?

Success criteria — I can:

describe the three states of matter in terms of particle arrangement and energy;
explain that melting and evaporation are both caused by thermal energy moving into a substance;
use conservation of matter to explain that evaporated water is still present as water vapor — it was not destroyed.

The puddle on the counter dries up completely. A student says, "The water was destroyed — it turned into energy." What is wrong with that explanation?

Re-teach: conservation of matter in a physical change Tier 3

Key rule: In a physical change (like melting or evaporating), matter changes its state — its arrangement — but the particles themselves are never created or destroyed. This is conservation of matter.

Evaporation is not a chemical reaction and does not convert matter into energy. What happened: the liquid water particles at the surface gained enough thermal energy from the warm room air to escape as individual gas particles (water vapor). They are now mixed invisibly into the air — too spread out and small to see, but still there.

Re-read option B, then think: if you trapped the room air in a giant sealed bag and cooled it down, what would appear on the inside walls of the bag? (Water — the same water that "disappeared.")

Reflect, then show what you know

Reflection metacognition · responsible decision-making

Think back to the moment in this lesson when your thinking shifted — when the popsicle "disappearing" stopped seeming like a mystery. What was the idea that changed your mind? Write one sentence describing it. (There is no wrong answer — the act of noticing when your thinking changes is a real scientific skill called metacognition.)

Exit ticket — answer on paper, on a sticky note, or in your notebook.

New A popsicle is a solid. The puddle it becomes is a liquid. Name the change that happened, and explain it in terms of particle arrangement and thermal energy.
New A student weighs a sealed bag containing a wet sponge. She leaves it on a sunny windowsill for a day, then weighs the sealed bag again. Will the mass go up, go down, or stay the same? Explain using conservation of matter.
Spiral — Week 1 Heat is particle motion. When the room air adds thermal energy to the popsicle, what exactly changes about the popsicle's particles?
Spiral — Week 2 Thermal energy transfers from warm to cold. Which direction does energy flow during the melting popsicle — into the popsicle or out of it? What does this tell you about the process (hint from Week 2: what do we call a process that absorbs energy)?
Transfer — preview Week 4 When wood burns in a fire, the solid wood turns to ash and smoke, and gases escape into the air. Is matter conserved? How is this similar to — and different from — the popsicle evaporating?

Educator panel — facilitation, accommodations, answer key

At a glance

Standard: NGSS MS-PS1-4 — Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed. 3D: SEP Developing & Using Models · DCI PS1.A Structure & Properties of Matter · CCC Energy & Matter (Conservation). Throughline: extends Week 1 (heat = particle motion) and Week 2 (energy transfer direction; endothermic) — students now apply both to explain a two-stage physical change and arrive at conservation of matter. Preview: Week 4 will extend conservation to chemical changes.

Materials (fully digital-capable): student notebook; optional physical materials — a popsicle or ice cube, a scale, and a sealed zip-lock bag can make Step 3's conservation argument concrete. The embedded SVG and worked example carry the instructional load without any physical materials.

Facilitation arc (Rosenshine)

Launch the phenomenon without vocabulary — ask "where did it go?" before defining evaporation (3 min).
Do-Now retrieval while taking attendance; cold-call Week 1 and Week 2 spirals (3 min).
Walk through Build Steps 1–3 with the worked example; stop for a quick pair-share after Step 2 ("what does thermal energy do to particles in a liquid?") (14 min).
Differentiated CER practice — circulate; note which tier supports students reach for and use that data for next-step feedback (15 min).
Self-check with branching; re-teach group for A/C responders on conservation (5 min).
Brain break, metacognitive reflection, exit ticket (10 min).

Common misconception to address: Many students believe evaporation means water "turns into nothing" or "turns into energy." Name it explicitly before or after the self-check: "This is one of the trickiest ideas in science — matter seems to disappear, but it only moves. We can't see individual gas particles, so our brains assume they're gone. They're not."

IEP / 504 accommodation cards

Common accommodations mapped to this lesson

Accommodation	How it's already built in / what to do
Text read aloud	Every core passage and Build step has a Listen button (TTS); simplified toggle shortens all text site-wide.
Reduced reading load	"Reading: Simplified" swaps in shorter plain-language text throughout.
Extended time / chunking	Lesson is organized into three numbered Build steps with checks between; progress saves automatically — students can stop and resume.
Sentence frames / word bank	Tier-2 panel under the practice task provides CER frames and a 10-word word bank.
Concrete analogy	Tier-3 "100 students in a gym" analogy + cloze sentence makes conservation tangible without lab materials.
Alternative response mode	Students may draw a labeled particle model, speak/record, or write the CER — all are accepted.
Behavior / focus (504, ADHD)	Named expectations (PBIS), the 30-sec check-in with self-rating, and a built-in brain break with a science-tied movement.
Multilingual / EL	Simplified text, SVG diagram carries meaning, word bank, and cognates: evaporation/evaporación, conservation/conservación, particle/partícula, vapor/vapor. Home-language reflection is always allowed.

Exit ticket answer key

Melting. The locked solid particles gained thermal energy from the room; they began moving fast enough to slide past each other, becoming a liquid — no longer in a fixed arrangement.
Mass stays the same. The water evaporated inside the sealed bag — its particles changed from liquid to gas (vapor), but they are still inside the bag. Conservation of matter: the total number of particles (and therefore mass) is unchanged inside a sealed system. (Note: if the bag were open, mass would decrease because the vapor would escape into the larger room.)
The popsicle's particles move faster. The added thermal energy increases the speed of particle motion — fast enough to eventually break the solid arrangement.
Energy flows into the popsicle from the warm room. This is an endothermic process: it absorbs energy. (Week 2 connection: thermal energy always transfers from warm to cold — the cold popsicle absorbs energy from the warmer room.)
Matter is conserved in both cases — no matter is destroyed. The difference: burning wood is a chemical change (new substances form — carbon dioxide, ash, smoke); popsicle evaporation is a physical change (same substance — water — just in a different state). Week 4 will explore whether conservation of matter still holds when new substances form (it does).

Why it's designed this way

Phenomenon-first question anchors student curiosity before vocabulary is introduced (NRC 2012 storyline pedagogy; Reiser et al. 2021). The three-step Build sequence uses explicit small-step instruction with a faded worked example (Sweller 1988; Rosenshine 2012). Conservation of matter is a persistent student misconception (Driver et al. 1994; the AAAS Project 2061 conceptual strand map places it as foundational before chemical reactions); the lesson confronts it explicitly with the sealed-container thought experiment rather than only implying it. Spiral exit items 3–4 invoke Week 1 (heat as particle motion) and Week 2 (endothermic energy direction), implementing interleaved retrieval practice (Roediger & Karpicke 2006; Rohrer 2012). The transfer item (burning wood, Week 4 preview) applies the same conservation principle to a new context — a low-stakes anticipatory set for the chemical-change unit (Bransford et al. 2000). The metacognitive "what changed my mind?" reflection targets responsible decision-making (CASEL) by prompting students to track their own reasoning quality, not just whether they got the right answer.