Why Puddles Disappear
Learners can explain evaporation as a kinetic-energy-tail process, describe how temperature, surface area, humidity, and airflow change its rate, and predict which conditions will make a puddle vanish fastest or slowest.
A complete interactive classroom, not just a preview.
Start when you are ready to enter this Stage's 12 scenes and explore, respond, and learn as you go.
Why does a puddle on the sidewalk disappear even on a cool day when the water never visibly boils?
- puddle-observation
- Puddles shrink and vanish even when no bubbles form, on calm cool days.
- molecular-motion
- Molecules in a liquid move with a spread of speeds; some have enough energy to escape the surface at any temperature.
- evaporation-mechanism
- Evaporation is the escape of high-energy surface molecules into the air; condensation is the reverse.
- vapor-pressure-equilibrium
- In a closed space, evaporation and condensation balance; in open air, molecules diffuse away and the net loss continues.
- rate-dependence
- Rate of evaporation increases with temperature, surface area, and airflow, and decreases as humidity approaches saturation.
- evaporation-vs-boiling
- Evaporation happens only at the surface, at any temperature; boiling is bubble formation throughout the bulk at the boiling point.
Evaporation only happens when water is heated or when it's hot outside.
Show that surface molecules can escape at any temperature, and that even cool puddles evaporate because the fastest molecules in the distribution leave first.
The sun's heat 'dries up' water by destroying it.
Distinguish observation (puddle disappears) from inference (water enters air as vapor, not destroyed) and establish that mass is conserved.
- basic idea that matter is made of particles
- everyday observation that wet things dry out
- exact Clausius-Clapeyron calculations
- intermolecular forces beyond a brief mention
- phase diagrams
- humidity formulas
- boiling point elevation
- Learner predicts which of two puddles disappears first given temperature, humidity, surface area, and wind.
- Learner explains in plain language why evaporation occurs below boiling, using the idea of a spread of molecular speeds.
- Learner identifies whether a new everyday example is evaporation, boiling, or condensation, and justifies the call.
- Apply the molecular model of evaporation to a new context such as why clothes dry faster on a windy day, why a covered drink stays cold longer, or why sweat cools the body.
Curious general learners aged 13+ with basic comfort reading science, but no prior chemistry coursework beyond everyday experience.
- 01The Disappearing Puddleslide
- 02Predict Before You Experimentinteractive
- 03Watch a Puddle Vanishinteractive
- 04What the Camera Can't Seeslide
- 05The Speed Lotteryinteractive
- 06Evaporation Has a Causeslide
- 07Covered vs Uncoveredinteractive
- 08Dry the Laundry: A Challengeinteractive
- 09Evaporation vs Boilingslide
- 10Spot the Processinteractive
- 11Recap and One Honest Uncertaintyslide
- 12A New Questionslide
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