Key Points

Water exists in three different states in daily life: solid (ice), liquid (water), and gaseous (water vapour). These states exhibit distinct properties and behaviors.

Melting is the process of conversion of a substance from its solid state into its liquid state upon heating. For example, ice melts to form water.

Evaporation is the process of conversion of water into its vapour state, which occurs continuously, even at room temperature. This explains why puddles disappear.

Common examples of evaporation include the drying of wet clothes, the disappearance of water from mopped floors, and the cooling effect of sweat on our bodies.

Condensation is the process of conversion of water vapour into its liquid state. This happens when water vapour comes into contact with a cold surface.

Water droplets forming on the outer surface of a cold glass tumbler, dew drops on plants, and water collecting on a pot lid are common examples of condensation.

Freezing is the process of conversion of a substance from its liquid state into its solid state upon cooling. For instance, water freezes into ice in a cold environment.

Ice (solid) retains its fixed shape, while water (liquid) takes the shape of its container and flows. Water vapour (gas) spreads to fill the entire available space.

The rate at which water evaporates is affected by the exposed surface area, temperature, and the movement of air. Larger exposed areas and higher temperatures increase evaporation.

Humidity, which is the amount of water vapour in the air, influences evaporation. High humidity, such as on rainy days, causes water to evaporate more slowly.

Evaporation causes a cooling effect because it absorbs heat from its surroundings as water changes from liquid to gas. This principle explains why water in earthen pots stays cool.

The pot-in-pot cooler utilizes evaporative cooling, where water seeping through the porous outer pot evaporates, drawing heat and cooling the contents of the inner pot.

Clouds form when water vapour in the air rises, cools, and condenses around tiny dust particles in the atmosphere, creating numerous small water droplets.

Many small water droplets within clouds join together to form bigger drops. When these drops become heavy enough, they fall to Earth as rain, hail, or snow.

The water cycle is the continuous circulation of water between the Earth's surface and the atmosphere. This involves processes like evaporation, condensation, and precipitation.

Only a small fraction of Earth's water is suitable for use by living organisms. Due to increasing population and demand, it is crucial to use water wisely and avoid pollution.