seegongsik
Grade 4 (age 9-10)

grade 4 States of Water

Ice taken out of the freezer melts into water, and if you boil that water in a kettle, it turns into steam and floats away. Ice, water, and water vapour are all the same water; only their form changes between solid, liquid, and gas depending on the temperature. Water can become vapour in two ways: evaporation, which happens slowly at the water's surface, like laundry drying, and boiling, which happens quickly with bubbles forming inside the water, like a bubbling kettle. Move the temperature slider to see how the movement of water particles changes, then compare evaporation and boiling in the lower picture.

The three forms of water

25°C
💧 The three forms of water
①Ice (solid): particles hold tight and only jiggle in place, so its shape stays fixed
②Water (liquid): particles slide past one another, so it takes the shape of its container
③Water vapour (gas): particles fly fast in every direction, and you cannot see it
④The higher the temperature, the faster the particles move

How are evaporation and boiling different?

🔥 Evaporation and boiling
①Evaporation is water turning slowly into vapour only at its surface; it happens even in cold water
②Boiling is water turning quickly into vapour not only at the surface but also inside, with bubbles forming
③Water boils at about 100 °C, and while it boils its temperature does not rise any further even if you keep heating it
④Laundry drying is evaporation, and a bubbling kettle is boiling

Condensation: vapour turning back into water

🪟 Vapour turning back into water
①Droplets form on the outside of a cold glass because water vapour in the air touches the cold glass and cools down
②This change of gaseous vapour into liquid water is called condensation
③A window steaming up on the inside in winter and dew on the grass early in the morning are condensation too
④The white cloud coming out of a kettle is not vapour but tiny droplets formed as the vapour cools in the air

Summary

Changes of state of water
Ice ↔(0 °C) water ↔(100 °C) water vapour
Depending on temperature, water changes between solid ↔ liquid ↔ gas
Names of the changes
Melting (solid → liquid) / evaporation · boiling (liquid → gas) / condensation (gas → liquid) / freezing (liquid → solid)
Each change has a name depending on which state turns into which
🎯 Key points
①Water has three forms: solid (ice), liquid (water), and gas (water vapour)
②Ice and water change into each other at 0 °C, and water and vapour at 100 °C
③Evaporation is slow and at the surface; boiling is fast and happens inside the water too
④Condensation is water vapour turning into droplets on something cold
⑤Even when its form changes, ice, water, and vapour are all the same substance

Examples and Unit Test

Example 1
What are laundry drying and a kettle bubbling as it boils?
1
Evaporation happens slowly, only at the water's surface, and it happens even at low temperatures.
2
Boiling happens quickly at about 100 °C, with bubbles forming inside the water. So drying laundry is evaporation, and the kettle is boiling.
▸ Laundry drying = evaporation / kettle bubbling = boiling
Both turn water into vapour, but they differ in where they happen and how fast.
Example 2
Why do droplets form on the outside of a glass holding a cold drink?
1
The air holds invisible water vapour, and when it touches the cold outside of the glass, it cools down.
2
The cooled vapour turns into tiny droplets; this is called condensation.
▸ Because water vapour in the air condenses (gas → liquid)
The water has not leaked from the drink; it came from the air outside.
Unit-test style
Which statement about changes of state of water is correct?
①Boiling happens only at the water's surface
②Condensation is water vapour turning into water
③Evaporation happens only at 100 °C
④When water freezes, it turns into a different substance
⑤Water vapour is water in its solid state
▸ ② Condensation is water vapour turning into water
1
Condensation is gaseous water vapour cooling and turning into liquid droplets.
2
Boiling happens inside the water too (①), evaporation happens at the surface at any temperature (③), frozen water is still the same substance (④), and water vapour is water in its gaseous state (⑤).
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