3. Properties of Natural Resources

Air is made of gases like nitrogen, oxygen, carbon dioxide and water vapour. These gases are mixed evenly. The composition of air is the same in all its parts. So air is a homogeneous mixture of gases.

Many solids, liquids and gases dissolve in water. No other liquid can dissolve so many substances. So water is called a universal solvent.

• Water dissolves many kinds of dirt.
• It flows easily and reaches every corner.
• Soap and detergent work only with water.
• Water is cheap and harmless.

So there is no alternative to water for cleaning.

• The humidity of the air will increase.
• We will feel sticky and uncomfortable. Sweat will not evaporate easily.
• Wet clothes will take a long time to dry.
• When the air cools, dew, fog or rain may form.

• The same nutrients will be used up again and again.
• The fertility of the soil will decrease.
• The yield of the crop will go down.
• Pests and diseases of that crop will increase.

So farmers should follow crop rotation.

Sandy soil has large particles with big gaps, so water drains away quickly.

Sea water contains dissolved salts, so it is a good conductor of electricity.

For example, salt dissolves in water, so water is the solvent.

Air presses on every surface, and this pressure is called atmospheric pressure.

The picture shows how rocks break due to freezing of water. Rain water collects in a crack in a rock. In cold weather, this water freezes into ice. Water expands on freezing. The ice pushes the walls of the crack outwards. So the crack becomes wider. This happens again and again. At last, the rock breaks into pieces. Slowly these pieces form soil.

Air contains tiny particles of dust, smoke and water. When light falls on these particles, they spread the light in all directions. This is called scattering of light. Because of scattering, the sky looks blue.

• Water is a fluid. It flows.
• It has no definite shape but has definite volume and mass.
• It is found in three states – ice, water and water vapour.
• It expands on freezing. So ice floats on water.
• Its density is 1 g/cc.
• Water has the highest density at 4 °C. This is its anomalous behaviour.
• It is a universal solvent.
• It is a good coolant.

Rain water is almost pure. It does not contain dissolved salts. Seawater contains a large amount of dissolved salts. These salts increase its mass. So the density of seawater is more than that of rain water.

The fertility of soil depends on its structure. Good soil has enough space between its particles.

• Roots get enough oxygen.
• Water drains well and does not stagnate.
• Roots spread easily and plants grow well.
• Earthworms and useful microbes live in it.

• Plants grow in soil.
• Soil holds water. So water can be stored with bunds and lakes.
• Wet soil can be moulded into pots, bricks and idols.
• China clay is used to make crockery and tiles.
• Shadu soil is used for idols. Terracotta soil is used for pots and decorative articles.
• Multani soil is used in cosmetics.

• Soil testing tells the farmer about the nutrients in the soil.
• It shows which nutrients are deficient.
• The farmer can use the right fertilizer in the right amount.
• From the pH, he can choose suitable crops.
• It keeps the soil fertile and increases the yield.

Sound needs a medium to travel. Air carries the vibrations of a sound to our ears. So we can hear sounds around us. On the moon there is no air. So no sound can be heard there.

Water expands when it freezes. A full bottle has no empty space for the ice to expand. So the ice pushes on the walls of the bottle. Glass cannot stretch. So the bottle cracks or bursts.

1. Soil is collected from different spots in the field. It is mixed well.
2. The soil is dried in the shade. It is crushed and sieved.
3. Its colour, texture, pH and nutrients are tested.
4. A report or soil health card is given. It tells which fertilizer to use.

Share these steps with your class and with farmers.