Ice melts. Puddles vanish. Cold glasses sweat. Water is always changing form, right in front of us.
Key idea
Ice and Water — Two States, One Substance
Leave an ice cube in a cup, and it turns into water. Ice and water are two forms — states — of the same substance.
Ice (solid)
Keeps its own fixed shape. Can be held, does not flow or spread.
Water (liquid)
Takes the shape of its container. Flows and spreads, but keeps the same volume.
Key idea
Evaporation
A puddle on the playground disappears by evening. A wet floor dries up. Where does the water go?
EvaporationThe process of conversion of water into its vapour state. It happens continuously, even at room temperature — the water turns into invisible water vapour, it doesn't just seep away.
Key idea
Condensation
Fill a glass with cold water and ice
soon, droplets appear on the outside. They aren't seeping through the glass; they're forming from water vapour in the air.
Condensation
The process of conversion of water vapour into its liquid state. Dew on morning grass, and droplets under a pot's lid, form the same way.
Key idea
Properties of Ice, Water, and Vapour
| Shape | Flows? | Spreads to fill space?
Ice (solid)Fixed — No — No
Water (liquid)Takes shape of container — Yes — No — keeps its volume
Water vapour (gas)None — Yes — Yes — fills all available space
Key idea
Melting, Freezing, Evaporating, Condensing
Ice (Solid) → Water (Liquid) → Water vapour (Gas)
Key idea
Faster or Slower Evaporation
1
More surface area
Water spread on a plate evaporates faster than the same water in a bottle cap.
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2
Higher temperature
Water in sunlight evaporates faster than water kept in shade.
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3
More wind
Clothes dry faster on a windy day than on a still day.
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4
Higher humidity slows it
Clothes dry slower on a rainy, humid day — the air already holds more water vapour.
Key idea
The Cooling Effect of Evaporation
1
The matka effect
Water seeps through the porous walls of an earthen pot (matka) and evaporates, cooling the water inside — steel pots don't do this.
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2
Everyday examples
Sweating and fanning cool our body as sweat evaporates. Sprinkling water on floors or roofs in summer cools the surroundings the same way.
Key idea
Clouds, Rain, and the Water Cycle
Evaporation from oceans & rivers
Water vapour rises and cools
Condenses into clouds
Falls as rain, hail, or snow
Chapter · Key terms to remember
Key Terms
Evaporation
Liquid water turning into vapour.
Condensation
Water vapour turning into liquid.
Melting
Solid turning into liquid.
Chapter · Key terms to remember
More Key Terms
Freezing
Liquid turning into solid.
Humidity
The amount of water vapour in the air.
Water vapour
The invisible gas form of water.
Chapter · Key terms to remember
More Key Terms
Water cycle
The continuous movement of water between Earth and the sky.
Questions for your notebook
Write these down, then discuss
1
Which best describes condensation? (i) Water converting to vapour (ii) Liquid changing to gaseous state (iii) Clouds forming from droplets (iv) Water vapour converting into its liquid state
2
In which is evaporation very important — (i) colouring with crayons, water colours, acrylic colours, or pencil colours? (ii) writing with pencil, ink pen, or ball point pen?
3
The space around natural grass feels cooler than the space around green plastic grass. Why?
Project as-is — students copy the questions, then the class discusses answers together.