Discover how water changes between solid, liquid, and gas through evaporation, condensation, and the water cycle.
Water’s Disappearing Act
Aavi and Thirav, two curious children, were playing in the school playground on a warm morning when they noticed something peculiar. In the early hours, there were small puddles of water scattered around the playground due to overnight watering of the garden. However, by the time they returned in the afternoon, these puddles had completely disappeared. This left them wondering: where did the water go?
Aavi, puzzled by the observation, suggested that the water might have seeped into the ground. However, Thirav pointed out that the playground had a concrete floor, which does not absorb water as soil does. Aavi then brought up another everyday observation—after washing steel utensils, a thin layer of water remains, but after some time, it disappears. This led them to wonder whether the missing water from the utensils and the playground had simply vanished into thin air.
To investigate further, they conducted a small experiment. They placed a few drops of water onto a steel plate and let it sit for some time. When they returned, they observed that the water was no longer present on the plate. Since steel is not absorbent, the water could not have soaked into it. This experiment led them to conclude that the water must have changed into another form and mixed with the air.
Understanding Evaporation
The phenomenon they observed is known as evaporation. It is the process by which water changes into its gaseous form, called water vapor, and disappears into the air. This process happens continuously, even at normal room temperature. Evaporation is responsible for various everyday occurrences, such as:
- Wet clothes drying on a clothesline as the water from the fabric slowly turns into vapor and escapes into the air.
- Water spilled on the floor disappearing without leaving any visible traces.
- Sweat on our skin evaporating, making us feel cooler.
Even though we cannot see water vapor in the air, we can feel its effects. For example, when we rub hand sanitizer on our hands, it dries quickly because the liquid alcohol in the sanitizer evaporates rapidly, leaving behind a cooling effect.
Another common way to observe evaporation is by heating water in a pan. After some time, we see steam rising from the surface. This steam consists of tiny water droplets formed when water vapor cools down, which brings us to our next phenomenon—condensation.
Water Droplets Forming on a Cold Glass – The Mystery of Condensation
One hot afternoon, Aavi and Thirav sat down to drink cold lemonade. Within minutes, they noticed tiny droplets of water forming on the outer surface of their glass. This puzzled Aavi, who wondered whether the water inside the glass was somehow leaking out. However, upon closer inspection, they found no cracks or leaks in the glass.
To explore this further, they placed an empty dry glass next to the cold one. The empty glass did not develop any droplets. So, where did these droplets on the cold glass come from?
Understanding Condensation
The answer lies in the presence of water vapor in the air. The air around us always contains some amount of moisture in the form of invisible water vapor. When warm air comes into contact with a cold surface, such as a chilled glass, the water vapor in the air cools down and turns back into liquid water. This process is called condensation. The tiny water droplets on the glass were formed by this process.
This phenomenon also explains why dew forms on leaves and grass during early winter mornings. At night, the temperature drops, causing the water vapor in the air to condense into tiny droplets on cool surfaces. Similarly, condensation is responsible for the foggy appearance of a bathroom mirror after a hot shower.
Another way to observe condensation is by covering a pot of boiling water with a steel plate. After some time, droplets of water form on the underside of the plate because the hot steam condenses upon touching the cooler surface.
Exploring the Three States of Water
Water is a unique substance because it can exist in all three states—solid, liquid, and gas—under normal conditions.
- Solid (Ice) – When water is cooled below 0°C, it freezes into ice. Ice retains its shape and does not flow like liquid water.
- Liquid (Water) – This is the most common state of water. It takes the shape of container in which it is filled.
- Gas (Water Vapor) – When water is heated, it evaporates and becomes an invisible gas called water vapor.
Many substances in nature undergo similar state changes. For example, wax melts when heated and solidifies when cooled, and coconut oil turns solid in cold weather but becomes liquid in warmer temperatures.
Factors That Affect Evaporation
Several factors influence the rate at which water evaporates:
- Surface Area
- The greater the surface area, the faster the evaporation takes place.
- Example: Water spilled on a plate evaporates faster than water in a cup because the plate has a larger surface area.
- Temperature
- Heat increases the rate of evaporation.
- Example: Wet clothes dry faster in summer than in winter.
- Air Movement (Wind)
- Wind carries away evaporated water molecules, allowing more water to evaporate.
- Example: Clothes dry quickly when hung in a breezy area.
- Humidity (Moisture in the Air)
- Higher humidity slows down evaporation because the air is already saturated with water vapor.
- Example: Clothes take longer to dry on a humid, rainy day.
How Evaporation Helps Cool Things Down
Evaporation has a cooling effect because it absorbs heat from the surrounding surface. This effect is noticeable in several everyday situations:
- Water stored in an earthen pot remains cool because some water seeps through the tiny pores of the clay and evaporates, absorbing heat in the process.
- People sprinkle water on floors during hot days to make the surroundings feel cooler.
- Sweating helps regulate body temperature as the sweat evaporates from the skin, taking away heat.
The Role of Water in Rainfall – The Water Cycle
The continuous movement of water through evaporation, condensation, and precipitation forms the water cycle, which is responsible for rain. The steps involved are:
- Evaporation – Water from oceans, lakes, and rivers turns into vapor due to the heat of the sun.
- Condensation – Water vapor rises and cools down, forming clouds.
- Precipitation – When the clouds become heavy, water falls back to the Earth as rain.
If the temperature is very low, precipitation occurs in the form of snow or hail instead of rain.
This natural cycle ensures that water is continuously reused on Earth. However, only a small portion of the Earth’s water is freshwater, making it crucial for humans to use water wisely and prevent water pollution.
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