📘 Chapter 8: A Journey through States of Water

• Answer: (iv) The conversion of water vapour into its liquid state.

• (i) Answer: (b) water colours
  Reason: Water present in water colours needs to evaporate for the paint to dry on paper.
• (ii) Answer: (b) ink pen
  Reason: Liquid ink contains water which evaporates, allowing the writing to dry quickly.

• Reason: Continuous evaporation of water takes place from the surface of natural grass and soil. Since evaporation produces a cooling effect by absorbing heat from the surroundings, the area around natural grass feels cooler.
• Plastic grass does not contain water, so no evaporation takes place from it. Thus, it gets heated up under the sun and does not create any cooling effect.

• Hand sanitiser
• Alcohol / Rubbing spirit
• Petrol and diesel
• Perfume / Cologne
• Nail polish remover (Acetone)

• Explanation: Evaporation depends on two major factors—temperature and air movement (wind).
• When a fan is switched on, the fast-moving air sweeps away the water vapour accumulated around the wet clothes.
• This increase in air movement speeds up the rate of evaporation, allowing wet clothes to dry quickly even if the air is cool rather than hot.

• Reduces Transportation Cost: Freshly removed sludge contains a large amount of water and is very heavy. When left in heaps for 3–4 days under sunlight and air, water evaporates, turning the sludge dry and significantly lighter in weight. Transporting dry, lightweight sludge reduces fuel and transportation costs.
• Enhances Handling Safety: Wet sludge is messy, slippery, highly foul-smelling, and prone to spilling or spreading pathogens. Once dried, it becomes solid, less hazardous, easier to manage, and much safer for workers to handle and transport.

Activities involving evaporation at home:

• Drying wet clothes on a clothesline.
• Mopping the floor and letting it dry.
• Sweating after physical work/exercise and drying off under a fan.
• Cooking or boiling tea/water.
• Cooling water stored in an earthen pot (matka).

How understanding evaporation helps:

• Understanding that a larger surface area speeds up evaporation helps us spread out wet clothes properly to dry faster.
• Knowing that air movement increases evaporation helps us turn on the ceiling fan to dry a freshly mopped floor quickly.
• It helps us utilize traditional cooling methods, such as sprinkling water on rooftops or using earthen pots in summer.

In nature, water is present in the solid state as:

• Ice and Snow: Found on mountain peaks, polar ice caps, and glaciers.
• Hail and Snowfall: Falling from clouds during cold weather or storms.

• Although Earth is covered mostly with water, only a very small fraction of freshwater is accessible and fit for human use.
• Due to rising population, industrial demand, and water pollution, freshwater scarcity is becoming severe in many parts of the world.
• If we only demand water as a right without fulfilling our duty to conserve it, water resources will deplete rapidly.
• Therefore, using water wisely, avoiding wastage, preventing water pollution, and harvesting rainwater is our primary responsibility before we claim water as our right.

• Solution: Sprinkle a small amount of water on the hot seat or wipe it with a wet cloth.
• Reason: The water on the seat absorbs heat from the hot surface and evaporates. As evaporation causes cooling, it rapidly lowers the temperature of the seat and cools it down.

• Wetting one hand with water and blowing air over both hands causes the wet hand to feel significantly cooler.
• Reason: Blowing air accelerates the evaporation of water from the wet hand, which absorbs body heat and creates a cooling sensation.

Prepare a short classroom or assembly play representing the stages of the Water Cycle:

• Evaporation: Sun heating river/ocean water into vapour.
• Condensation: Vapour cooling down around dust particles to form clouds.
• Precipitation: Clouds becoming heavy and falling as rain/snow.
• Collection: Rainwater flowing back to rivers and oceans.