Maharashtra Board Class 4 EVS Chapter 9 Air PDF Download

Air

Can You Tell?

What are the people in the pictures doing?

Try This

Take water in a big container.

Take a small narrow container.

Hold it upside down on the surface of the water and without tilting it, push it down into the water.

Now allow it to tilt.

What Do You See?

Bubbles rise at once to the top.

What Does This Tell Us?

Air is lighter than water. So air bubbles rise to the top as soon as the container is tilted.

It means that there was air even in the container that appeared to be empty.

There is air all around us. It is present even in places that appear to be empty. Then, how far around us does air spread?

Teacher's Note

This experiment shows that air is everywhere. Like how we cannot see air but breathe it, air fills the empty container too.

Exam Trick

Remember: Air is present everywhere, even in "empty" containers. When the container tilts, air bubbles come out because air is lighter than water.

Points to Remember

Air is all around us.
Air is lighter than water.
Air can be trapped in empty spaces.
Bubbles show that air was in the container.

Try This

Take large sheets of any waste paper. Or, obtain old newspapers of about one month and tear each of the sheets into four pieces. Now place these sheets of paper one at a time in a pile on the floor.

As the pile grows, observe the difference that can be seen in the layers of paper at the top of the pile and those near the floor.

What Do You See?

As we place more and more papers on the pile, the sheets at the lower level are pressed down by the sheets above them. The distance between the papers in the lower part of the pile becomes less while the papers in the upper part appear to be further apart.

What Does This Tell Us?

The nearer a sheet of paper is to the floor, the greater is the number of papers above it. It means that the lower layers bear more weight than the upper layers of paper. Compared to that the upper layers bear less weight.

Teacher's Note

This shows how weight pushes down. The papers at the bottom feel heavy because many papers are on top of them, just like how people at the bottom of a pile feel pressure.

Exam Trick

Remember: Lower layers = more weight on top. Upper layers = less weight. This is why papers compress more at the bottom.

Points to Remember

Lower layers have more papers above them.
Lower layers are pressed together more.
Upper layers have less pressure on them.
Weight increases as you go down.
More papers above means more compression below.

Try This

Take a slightly deep dish like a saucer.

Stand a candle at its centre.

Fill water in the dish.

Light the candle.

Now place a glass tumbler over the candle.

What Do You See?

Soon the candle goes out and the level of water inside the tumbler rises up to a certain level.

Why Does This Happen?

One of the constituents of air helps burning. As it gets used up, water rises in the tumbler. When that constituent is finished, the candle goes out. The water level too stops rising.

Teacher's Note

This shows that air has oxygen which helps things burn. When oxygen is used up, the candle stops burning, like how a lamp stops burning when there is no oil.

Exam Trick

Remember: The candle burns and uses oxygen. When oxygen is used up, candle goes out and water rises. Oxygen helps burning.

Points to Remember

Air has a gas that helps burning.
This gas is called oxygen.
When oxygen is used up, candle stops burning.
Water level rises when candle burns.
Water fills the space where oxygen was used.

The Atmosphere

The earth on which we live is round in shape like a ball. There is air all around the earth. If we go higher above the earth, we find that there is air till a height of almost 50 km.

This covering of air around the earth is called the atmosphere.

As we go farther from the earth, the layers of air become thinner. That is, the layers of air closest to the earth are very close to each other, while the ones at higher levels are not so close. The air at greater heights is rare.

Teacher's Note

The atmosphere is like a blanket around Earth. It is thick near the ground where we live and becomes thinner as we go up, just like how a blanket is heavy on top of you.

Exam Trick

Remember: Atmosphere = air around Earth. It goes up to 50 km. Layers near Earth are thick and close together. Layers above are thin and rare.

Points to Remember

Atmosphere is air around Earth.
It extends about 50 km high.
Lower layers are thick and close.
Upper layers are thin and rare.
Air is present in the entire atmosphere.

The Composition Of Air

This constituent of air that helps burning is called oxygen gas.

The earth's atmosphere is made of air. The circle in this picture shows all the air in the atmosphere. If we divide the circle into five equal parts, then the oxygen in the air will be equal to one of the parts.

Apart from oxygen, there are other gases in the atmosphere. Which could those be?

The oxygen in the air is used both for burning as well as respiration.

Which are the other uses of air you know about?

You have learnt that the gas that fizzes out of soda-water is carbon dioxide. This gas is present in small quantities in air, too. You have also learnt that plants make their food using air and water in the presence of sunlight. When plants make their food, they use the carbon dioxide from the air.

You have seen that when you place ice in a glass and it becomes very cold, droplets of water settle on its outside. It means that water, too, is present in air in the form of a gas.

However, the largest part of air is made up of still another kind of gas. This gas is called nitrogen.

Thus, there are several gases present in air. In other words, air is a mixture of several gases.

Now if we draw a circle to represent air, then the quantity of each gas in the mixture will be as shown alongside.

Teacher's Note

Air has many gases mixed together. The biggest part is nitrogen, then oxygen. It is like a fruit juice that has many fruits mixed in it.

Exam Trick

Remember: Air = mixture of gases. Nitrogen is the most. Oxygen is one-fifth. The rest are very small amounts. Think: Nitrogen = 4 parts, Oxygen = 1 part out of 5.

Points to Remember

Air is a mixture of several gases.
Nitrogen is the largest part of air.
Oxygen is one-fifth of air.
Carbon dioxide is a small part of air.
Water vapor is also present in air.

Do You Know?

The burning that takes place in factories, vehicles, stoves in kitchens, etc. gives out smoke. This smoke, too, mixes with the air around us.

This is a preview of the first 3 pages. To get the complete book, click below.