Master Chapter 8 Class 6 - A Journey through States of Water (Curiosity) with comprehensive NCERT Solutions, Practice Questions, MCQs, Sample Papers, Case Based Questions, and Video lessons.
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Welcome to Chapter 8. Our journey begins on a bright summer afternoon with two friends, Aavi and Thirav, enjoying a glass of shikanji (lemonade). As they look at the ice cubes floating in their drink, a simple observation sparks a big scientific debate.
Thirav makes a very logical point: "Ice feels hard and we can hold it... whereas, water flows and cannot be held in the same way. So, they must be different substances."
Aavi disagrees, suggesting they are actually the same substance. Thirav is still skeptical; maybe, he thinks, "something gets added to the ice in the freezer."
This simple argument is the starting point for one of the most fascinating investigations in all of science. This chapter is a journey to solve this mystery and many others. We will follow water as it changes its form, disappears into thin air, and reappears as if by magic. We are about to explore the three states of water.
This chapter is a series of fascinating mysteries. Each time we solve one, a new, more interesting question appears. We will become water detectives, following the clues to understand the rules that govern this incredible substance.
We will start with Thirav's question. We will conduct a simple experiment: we will take an ice cube (which we know is hard and holds its shape) and simply leave it on a table. As we watch, it will slowly melt and turn into a puddle of water (which is liquid and flows).
This simple observation proves that Aavi is right. Ice and water are not different substances; they are just two different forms, or states, of the same substance.
Ice is the Solid State of water.
Water is the Liquid State of water.
This act of changing from a solid to a liquid is a process we will learn about called melting. But as soon as we solve this, a new mystery appears.
It is a rainy morning, and the playground is full of water puddles. But when Aavi and Thirav go out to play in the evening, the puddles are gone. Where did the water go?
Thirav's first guess is that the water seeped into the soil. This is a good hypothesis. But Aavi brings up a new puzzle:
What about wet clothes hanging on a clothesline? The water disappears from them, too.
What about a floor that has just been mopped?
What about water left on a steel plate after washing?
The water disappears from all of them, and it is not seeping into the steel plate or the clothesline. So, where is it going?
We will discover that the water is changing into a third state, an invisible, gaseous state called water vapour. This process, where a liquid turns into a gas, is called evaporation. We will learn that this process is happening all the time, invisibly, all around us. When you sprinkle water on a hot dosa pan, it disappears instantly—that is very fast evaporation!
Now that we have discovered three states (solid, liquid, and gas) and two processes (melting and evaporation), we will stumble upon the biggest mystery in the entire chapter.
Aavi and Thirav make lemonade again. They take a glass tumbler, fill it with cold water, and add ice. They leave it on the table. After a few minutes, they notice something bizarre: tiny water droplets are appearing and running down the outside of the glass.
Now, we have a real puzzle. Where did this outside water come from?
Did the ice somehow come out of the glass? Impossible.
Did the water seep through the tiny, invisible pores of the glass? This is a great scientific question, and we will design an experiment to test it.
We will conduct an activity where we place a cold, sealed glass on a sensitive digital weighing balance. What we will find is astonishing: the weight of the glass increases over time. This proves water is not seeping out; rather, new water is being added to the outside from the air itself!
This leads us to a huge discovery: the air all around us is filled with invisible water vapour. When this water vapour (a gas) comes in contact with the cold surface of the glass, it gets cooled down and changes back into a liquid. This process, the opposite of evaporation, is called condensation.
Those droplets on the outside of your cold drink are not from the inside of the glass; they are from the air. The same thing happens when you see dew drops on leaves in the morning.
This chapter is full of these invisible processes and "cause-and-effect" connections—ice melts when heated, water evaporates into the air, vapour condenses on a cold surface. It can be a lot to connect, especially when the most important parts (like water vapour) are invisible.
This is precisely where Teachoo becomes your most valuable guide. We are masters at taking these complex, invisible cycles and breaking them down into simple, logical steps. We help you see the "how" and "why" behind each process, connecting evaporation to condensation, and showing you how this journey of water forms the basis for our entire planet's weather system. We make the invisible visible.
Once we have solved these three mysteries, we will have a complete picture of water's journey. We will know all its states and all its transitions:
Solid (Ice) $\rightarrow$ Melting $\rightarrow$ Liquid (Water)
Liquid (Water) $\rightarrow$ Freezing $\rightarrow$ Solid (Ice)
Liquid (Water) $\rightarrow$ Evaporation $\rightarrow$ Gas (Water Vapour)
Gas (Water Vapour) $\rightarrow$ Condensation $\rightarrow$ Liquid (Water)
We will also investigate how to control these processes. We will ask:
How can we make evaporation faster? We will discover three key factors:
Temperature: Water evaporates faster in the sunlight than in the shade.
Surface Area: Water in a plate (large area) evaporates faster than in a bottle cap (small area).
Wind: Clothes dry faster on a windy day because the wind carries away the water vapour.
How can we make evaporation slower? We will learn about humidity—the amount of water vapour already in the air. On a rainy (very humid) day, evaporation is very slow, which is why it is so hard to dry clothes.
This investigation leads to a final, amazing discovery. We will ask: why does water in a matka (an earthen pot) stay so much cooler than water in a steel pot?
The answer is evaporation! The earthen pot has tiny, microscopic pores. A tiny amount of water seeps through these pores to the outside surface and then evaporates. This act of evaporation uses energy, which it pulls from the pot and the water inside, making the water colder. This is called the cooling effect.
This is the exact same reason why you feel cool when you sweat. The sweat on your skin evaporates, and this process cools your body down. A fan makes you feel cooler not by blowing cold air, but by making your sweat evaporate faster!
Finally, we will take everything we have learned—evaporation, condensation, and water vapour—and use it to answer the biggest question of all: How do clouds give us rain?
We will see that the entire planet is a giant version of our experiments:
Evaporation: The sun heats the oceans and lakes, and water evaporates, turning into water vapour.
Rising Vapour: This water vapour is light, so it rises high into the atmosphere.
Condensation: High up, the air is very cold. The water vapour condenses around tiny, floating dust particles, turning back into microscopic liquid water droplets.
Cloud Formation: These billions of tiny, floating droplets clump together to form the clouds we see.
Rain: The droplets in the clouds continue to join together. Eventually, they become so big and heavy that the air cannot hold them up anymore, and they fall to the Earth as rain.
This constant, beautiful movement of water from the oceans to the sky and back to the land is known as the water cycle. It all starts with the same simple processes you can see in a puddle, on a cold glass, or in a matka in your kitchen.
From a single glass of shikanji, we will have gone on a journey to understand the clouds.
To get started on this amazing journey, click on any topic link to begin your exploration.