This is where the model earns its keep — explaining things you've seen a hundred times, and then the real test: being handed the result and reasoning back to the cause.
Why You Can Smell Dinner from Your Bedroom
Nobody fans the smell of cooking down the hall — it travels on its own. That's diffusion: the smell is gas particles, flying in every direction and bouncing off everything, and over time that random racing carries them from crowded (the kitchen) to empty (your room) until they're everywhere. Only a gas does this so freely, because only a gas has the big empty gaps to spread into. Press the puff in the toy and watch the particles wander out to fill the space all by themselves.
Three More You've Definitely Seen
A balloon shrinks in the freezer: no air escapes, the cold just steals energy, so the particles slow down, hit the walls less hard and less often, and the balloon caves in a little. Condensation beads on a cold drink because warm water-vapour particles bump the cold glass, lose energy, slow down and clump back into liquid. And a hot-air balloon rises because heating the air inside spreads its particles further apart, making that air less dense than the cooler air outside.
The Real Skill: Reasoning Backwards
Rung 2 went forwards — cause to effect. Mastery is going backwards: you're handed the effect and you reconstruct the particle story. A sealed packet of chips puffs up tight on a plane. Work back: it didn't gain particles, so the gas inside must be pushing harder — the cabin air is lower pressure up high, so the trapped gas meets less squeeze and balloons the bag. Wet washing dries without ever boiling. Work back: liquid became gas, so particles left the surface — the fastest ones escape into the air as vapour even well below boiling. That's evaporation, and it's why a breeze and a sunny day speed it up: more energy, more escapees. Take on the scenario cards in the toy and talk each one back through the particles.
A Depth-study Thread
This is a lovely launch pad for a Year 7 depth study (the scope sets aside time for one): design a fair test of what makes a puddle evaporate fastest — surface area, temperature, or wind — changing one thing at a time and measuring. It's real working scientifically (SC4-WS-04, SC4-WS-07) hanging off a particle idea.