Air, water and weather
The weather keeps on changing from day to day. Even on same day, we can have cloudy weather or rainy day. Weather is the condition of air, clouds, rain and sun at a particular time at a particular place. The weather can be sunny, windy, rainy or cloudy.
The sun causes changes in weather
The weather changes due to the heat of the sun. The sun affects the temperature and length of the day and night at a particular place. Let us see how.
- We know that the Earth moves around its own axis. This is called rotation. The part of the Earth facing the sun has day and the part away from the sun has night. So, days are warmer because of the heat of the sun and nights are cooler.
- The Earth also moves around the sun. This movement is called revolution. This revolution causes the change in seasons. The part of the Earth closer to the sun has longer and hotter days and has summer. The part of the Earth away from the sun has cooler and shorter days and thus it has winter.
- The sun also causes wind to blow. Due to the heat of the sun, the air gets heated up and it becomes lighter. This hot, lighter air rises up and the cool air moves in to take its place. This movement of air is called wind.
The sun also changes states of water into water vapor and vapor to water and to ice. This results in the change in weather.
On a rainy day, you must have observed that we feel sticky because our sweat (water) does not get evaporated as there is too much of water vapor in the air. This weather is called humid weather. The amount of water vapor present in the air is called humidity.
The heat of the sun changes water into water vapor. Then vapor condenses to form drops of water. Tiny drops of water join together to form clouds. When these clouds become heavier, they fall down on the Earth as rain. When these raindrops pass through a very cold region, they fall down on the Earth as snow.
Sun changes weather
More about air
Our Earth is surrounded by an envelope of air called the atmosphere. Air is a mixture of several gases, water vapor and dust particles.
When the wind moves gently, it is called a breeze. When the winds are accompanied by dust, they are called dust storms. If there is thunder and lightning with the storm, they are called thunderstorms. Wind affects the weather of a place.
Land breeze and sea breeze
In coastal areas, we can experience land breeze and sea breeze. The land gets heated faster than water. During the daytime, the heat of the sun falls on water and land equally, but land gets heated faster. So, the hot air rises up and the cool air from the sea moves towards the land to occupy the empty place. Thus, a cool breeze blows towards he land during the day. This is called sea breeze.
During night-time, land cools down faster than the sea. So, the hot air from the sea rises up and the cool air from the land moves towards the sea. This is called a land breeze.
More about water
We know that 70 % of the Earth's surface is covered with water. In nature, water exists in three forms - solid (snow), liquid (water) and gas (vapor).
The heat of the sun changes water into water vapor. This process is called evaporation.
What happens when your mother washes the balcony with water. After some time, you can see the wet floor dries up. Where has that water gone ? The water has evaporated. The rate of evaporation is faster
- when a strong wind is blowing.
- when the wet clothes dry faster on a windy day.
- when the exposed surface is larger: A folded hanky takes more time to dry but if the hanky is spread open, it dries faster.
- when the temperature is high. On a sunny day, evaporation is faster.
- when the air is dry: On a dry day, our sweat gets evaporated faster than on a rainy day.
We get rain because the water vapor of clouds condenses into water. Take a glass filled with ice - cold water. Keep it for some time. What do you see ?
We can see droplets on the outer wall of the glass.
You must have observed the drops of water on a leaf on cold water mornings. This is called dew.
Impurities in water
Rainwater is the purest form of water. But the river water and well water are not pure.They contain different types of impurities in it. They are of three types:
- Soluble impurities which we cannot see they are dissolved in water.
- Insoluble impurities which can be seen.
- Germs and disease-causing micro-organisms are also present in water.
The insoluble impurities can be separated be the following methods:
Allow the impure water to stand for some time. The heavier insoluble impurities like sand, mud, etc. will settle down and the clean water is left on the top. This is called sedimentation.
The clear water obtained by the process of sedimentation can easily be poured into another beaker. This process is called decantation.
Take a filter paper, fold it in a layer of 4 and set it in a funnel. Keep the funnel properly on a beaker. Now, pour the impure water in the funnel. The impurities will stick in the filter paper and clean water will be collected in the beaker.
The process of adding chlorine to water is called chlorination. Chlorine tablets can also be added to water to kill the germ. A few drops of potassium permanganate can also kill the germs.
Boiling can also kill germs present in water.
Do you know ?
We use water filter at home to filter the water. The candles of these filters are made of porous material which help to filter the water.
How to store water ?
- Clean water must be kept in a clean vessel which is covered.
- Always take out water with the help of a mug.
- The water container should be kept in a neat and clean place. Do not keep them near bins.
Precious natural resource
Water is a precious natural resource. We should use it carefully. We should not waste water.
- Turn off the tap while brushing your teeth.
- You can use the leftover water from the water bottles to water the plants.
- Water the plants using a mug and bucket. Avoid using a hose-pipe to save water.
Points to remember
- Weather keeps on changing from time to time.
- The sun is responsible for the change of weather.
- The heat of the sun causes land breeze and sun breeze.
- Evaporation and condensation of water also cause rainfall.
- Water may contain different types of impurities which can be removed by sedimentation, decantation, filtration or boiling.
- water is precious natural resource. It should be used properly and should not be wasted.