CLASS 6 SCIENCE · CHAPTER 8 · STUDY NOTES
A Journey through States of Water
Trace evaporation, condensation and cooling, then connect them with clouds and the water cycle.
01 / EXPLORE & UNDERSTAND
One substance, three states
Ice, liquid water and water vapour are different states of water.
1. Compare how shape changes
An ice cube keeps its own shape when moved to another bowl, until it melts. Liquid water flows and takes the shape of the part of the container it occupies. Pouring it carefully changes its shape, not the amount.
2. A gas spreads through available space
Water vapour is a gas and is invisible. It can mix with the surrounding air. The visible white mist near a steaming vessel consists of tiny liquid droplets, not visible gas.
Your turn
Question
Why is a white cloud above a hot drink not proof that water vapour itself is white?
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02 / EXPLORE & UNDERSTAND
Where did the puddle go?
A puddle can shrink through more than one process.
1. Separate soaking in from evaporating
On soil, some water can soak into the ground while some evaporates into the air. A dry patch alone does not tell you how much followed each route.
2. Use a surface water cannot soak through
A little water on an intact steel plate can dry even though it does not seep through the metal. It becomes vapour. Wet clothes and a mopped floor can dry at room temperature: boiling is not required for evaporation.
Your turn
Question
A metal spoon dries after washing without becoming hot. Which process explains this?
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03 / EXPLORE & UNDERSTAND
Drops outside a cold glass come from the air
The cold surface helps water vapour in nearby air turn into liquid drops.
Inside water and outside droplets are different
1. Identify both sides of the glass
The drink is inside. The new droplets form on the outside, where moist air touches the cold surface. They need not be liquid leaking through the glass. Dew on a cool leaf is another example of condensation.
2. Test an explanation with several observations
Compare a cold dry-sided container with a similar one at room temperature. Track outside droplets and the whole setup’s mass. Added drops can increase the mass. Keep other conditions controlled; one rough level reading alone is not a complete test for every possible leak.
Your turn
Question
Why would droplets on a cold, sealed metal container support condensation rather than water passing through glass?
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04 / EXPLORE & UNDERSTAND
Name the change in the correct direction
A process name describes where water starts and where it ends.
1. Follow warming and cooling
Ice gains energy and melts into liquid water. Cooling water enough removes energy and allows it to freeze. The freezer does not add a new substance to make ice.
2. Keep the two liquid–gas words separate
Liquid becoming vapour is evaporation; vapour becoming liquid is condensation. These directions are opposite. Melting ice does not turn it directly into the visible drops on the outside of a separate glass.
Your turn
Question
A freezer tray contains liquid at first and solid later. Name the change and explain what the freezer does.
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05 / EXPLORE & UNDERSTAND
Spread out the same amount
Water usually evaporates faster when more of its surface is exposed to the air.
1. Change one condition
Put equal small amounts of water in a narrow cap and a wide shallow dish. Keep them beside each other so conditions are similar. The wide dish exposes more water surface.
2. Record before concluding
Compare how long each takes to dry. If water amounts, wind or temperature differ as well, you cannot confidently give all the difference to surface area. Repeat the comparison if a spill changes the amount.
Your turn
Question
A full plate and one drop in a cap are compared. Is that a fair test of surface area alone?
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06 / EXPLORE & UNDERSTAND
Warmth, moving air and humidity
Drying depends on the surroundings as well as the wet object.
Compare sunlight and shade
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1. Warmth and moving air often speed drying
Warmer conditions generally increase evaporation. Moving air carries moist air away from the wet surface, allowing further evaporation. That is why spreading clothes and leaving space for air can help.
2. Moist air makes further evaporation slower
With other conditions similar, evaporation is slower when the surrounding air is more humid. Rainy days are often humid. A fan can help drying by moving air even if it does not heat the room.
Your turn
Question
Why can a fan help dry a damp cloth without producing hot air?
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07 / EXPLORE & UNDERSTAND
Evaporation can cool the surroundings
Evaporation needs energy. It can take that energy from the water and nearby surroundings.
An earthen vessel uses evaporation
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1. Connect sweat with cooling
Sweat that evaporates can take energy from your skin and cool it. Sweat simply dripping off is not the same process. Moving air can help evaporation, although high humidity can reduce the effect.
2. Follow water through an earthen pot
A little water reaches the outside through tiny pores in an unglazed earthen pot. As it evaporates, it cools the pot and the water inside. A steel pot does not let water seep through its wall in the same way.
Your turn
Question
Why does painting over the outside pores of an earthen pot reduce its cooling action?
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08 / EXPLORE & UNDERSTAND
A cooler without electricity
A pot-in-pot cooler uses the same evaporation idea on a larger wet surface.
Read the layers from inside out
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1. Locate the wet layer
The small pot holds the contents. Wet sand fills the space between pots. Water supplied to this layer can reach the outer pot and evaporate. A cover helps protect the contents.
2. Explain what limits the cooling
The wet layer must be maintained. Air movement and humidity affect the cooling, so it is not a refrigerator with a fixed temperature. Do not assume every food stays safe for the same number of days.
Your turn
Question
The sand has dried completely. Why might the cooler stop cooling effectively?
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09 / EXPLORE & UNDERSTAND
Clouds contain tiny droplets or ice crystals
Invisible vapour must change before we see a cloud.
1. Cooling helps cloud droplets form
When moist air rises, it often cools. Water vapour can condense onto tiny airborne particles. Many small liquid droplets, or ice crystals in cold conditions, make a visible cloud.
2. Drops must grow enough to fall
Droplets can combine and grow. When large enough, they fall as rain. Snow and hail involve freezing processes too; they are not simply liquid rain with a different name. Clouds can also move with the wind before precipitation reaches the ground.
Your turn
Question
Why is calling a cloud “a bag full of invisible water vapour” incomplete?
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10 / EXPLORE & UNDERSTAND
Water takes many connected routes
The water cycle is a set of connected movements and changes—not a queue every drop must follow.
Follow the labelled routes
1. Connect the routes
Water evaporates from oceans and land. Condensation forms droplets; precipitation returns water. Some flows in rivers, some soaks into the ground, and some stays stored as ice, in lakes or underground. Plants also release water vapour.
2. Circulation does not remove the need to save water
Most Earth water is salty ocean water. Usable fresh water is limited and unevenly available. A cycle does not guarantee clean water at the place and time people need it. Avoid waste and keep water bodies free of pollution.
Your turn
Question
Why can a town face water shortage even though the water cycle continues?
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Sign inNew here? Sign up freeCHAPTER RECAP
Take these ideas with you
- Ice, liquid water and invisible vapour are states of the same substance.
- Evaporation changes liquid to vapour; condensation changes vapour to liquid.
- Melting and freezing connect the solid and liquid states.
- Surface area, temperature, air movement and humidity affect evaporation.
- Evaporation can take energy from surroundings and cool them.
- The water cycle connects many routes, but clean usable water must still be conserved.
Use your understanding in a new situation
Question
A sealed cold bottle becomes wet outside while its contents stay inside. Explain the starting and ending states of the new outside water.
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Sign inNew here? Sign up freeQuestion
A wide dish dries faster than a narrow cup. What information would you need before saying surface area caused the difference?
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Sign inNew here? Sign up freeNCERT · Chapter source PDF, pages 17, 18, 19, 20 · Original Learnijoy explanations and practice.