Properties of Natural Resources | Class 7 | Science | Chapter 3 | Maharashtra State Board
This educational video explores the properties of natural resources, including air, water, and soil. The video begins by explaining the mass, weight, and atmospheric pressure of air, and includes hands-on activities to help viewers understand these concepts. Next, the video delves into the properties of water, including its anomalous behavior and density calculation. The importance of soil and its properties are also discussed, including soil texture, structure, and fertility. Viewers will learn how to test soil and identify factors that can diminish soil fertility. This informative video is designed to help viewers understand the properties of natural resources and their importance in our daily lives.
Questions & Answers
1. Fill in the blanks with the appropriate term.
(Temperature, volume, mass, density, humidity, acidic, weight, neutral, shape.)
The capacity of air to hold moisture depends upon the temperature of the air.
Water does not have a shape but has definite volume and mass.
While freezing, the density of water is lowered.
Neutral soil has pH 7.
2. Why is it said that -
(a) Air is a homogeneous mixture of various gases.
Ans. Air is made of oxygen, nitrogen, carbon dioxide, water vapor and dust particles. All these are in different proportions. Therefore air is a homogeneous mixture.
(b) Water is a universal solvent.
Ans. Water dissolves more substances than any other liquid. It dissolves solids, other liquids and even gases in it. Therefore, it is called as Universal solvent.
(c) There is no alternative to water for cleaning purposes.
Ans. Water is a universal solvent. It dissolves more substances than any other liquid so there is no alternative to water for cleaning purposes.
3. What will happen if…
(a) The amount of water vapor in the air increases.
Ans. We feel the dampness or the humidity.
(b) Only one crop is grown repeatedly in the soil.
Ans. The fertility of the soil decreases.
4. With whom should I pair up?
Group 'A' | Answer | Group 'B' |
Air | Scattering of light | Excretion |
Water | Excretion | Scattering of light |
Soil | Plasticity | Plasticity |
5. State whether the following statements are true or false.
(a) Sandy soil has low capacity for holding water.
Ans. True.
(b) The substance in which a solute dissolves is called a solvent.
Ans. True.
(c) The pressure exerted by air is called atmospheric pressure.
Ans. True.
(d) Sea water is a bad conductor of electricity.
Ans. False. (Sea water is a good conductor of electricity.)
6. Explain the picture in your own words.
Ans.
Diagram (a): Water is filled in the crack.
Diagram (b): Water in the crack turns to ice due to decrease in temperature. When it turns to ice the volume increases and it expands. Due to expansion, the size of crack widens more than in diagram (a).
7. Write answers to the following questions in your own words.
(a) How is light scattered by the air?
Ans. Air is a mixture of very fine particles of some gases, dust, smoke and moisture. When rays of light fall on these minute particles, the particles spread the light in all the directions. This natural phenomenon is called scattering of light.
(b) Explain the various properties of water.
Ans. Various properties of water are as follows:
It is a fluid substance because it can flow.
It does not have its own shape, it takes the shape of a container in which it is kept.
It has a definite volume.
It is a transparent liquid and it has no color.
It is tasteless and odorless.
It is a universal solvent.
(c) Why is the density of seawater more than that of rain water?
Ans. Seawater has many minerals dissolved in it as compared to rainwater. So due to more dissolved salts, density of seawater is more than that of rainwater.
(d) What is the importance of good soil structure?
Ans. The fertility of soil depends upon soil structure. So importance of good soil structure is as follows:
(a) Roots get sufficient supply of oxygen.
(b) Water drainage is good therefore the roots of plants grow well.
(e) What are the various uses of soil ?
Ans. The uses of soil are as follows:
Plant conservation: To help plants grow.
Water conservation: Soil holds water. As a result, by means of bunds and lakes, we can get water for use throughout the year.
Plasticity: Soil can be given any required shape. This property of soil is called plasticity. Because of its plasticity, we can use it to make articles of a variety of shapes. These articles can be baked to make them hard, Water storage earthen pots, earthen lamps, idols, bricks etc. are articles made from soil.
(f) What is the need and importance of soil testing from the point of view of farmers?
Ans. The properties of the various ingredients of soil can be determined by soil testing.
During soil testing, the soil is examined for colour, texture and the proportion of organic matter in it.
Soil is tested to find out if there is a deficiency of any ingredients and to decide what measures should be taken to remove the deficiency. These information would enable the farmers to maintain the fertility of the soil.
(g) What is the importance of air in transmission of sound?
Ans. Air is useful as a medium for the transmission of sound. Density of the air changes with temperature. If the density of air increases, we can hear the sound more loud and clear.
(h) Why should a glass bottle completely filled with water never be kept in a freezer ?
Ans. Due to anomalous behavior of water, when you cool water below 4°C, the volume of the water increases. Therefore when the glass bottle completely filled with water is kept in a freezer, water expands on cooling and its volume increases so glass bottle breaks. To avoid this, completely filled bottle is never kept in a freezer.
E X T R A
1. Fill in the blanks.
Air is a mixture of gases.
Atmospheric pressure is the same in all the directions.
Barometer is used to measure atmospheric pressure.
As we go higher the sea level, the atmospheric pressure decreases.
Pressure of air increases when its velocity decreases.
Wind an effect of the difference in air pressure.
The level of humidity in the air is determined by its capacity to hold water vapour.
When the temperature of air is low, its capacity to hold the vapour is less.
Air is useful as a medium for the transmission of sound.
Water is a fluid substance.
Ice is lighter than water.
Density of ice is less than that of water.
The space occupied by a substance is its volume.
The storage of matter in a substance is its mass.
The density of water is maximum at 4 °C.
The substance in which the solute dissolves is called solvent.
The particles of sandy soil are made of the mineral called Silicon dioxide.
Clay soil has a highest water holding capacity.
Terracotta soil is red in colour.
Multani soil is used in cosmetics.
5th December is celebrated as World Soil Day.
2. Answer the following.
(a) What is atmospheric pressure?
Ans. The molecules of the gases in the air are in constant motion. When these molecules strike a body, they create pressure on that body. This pressure of air is called atmospheric pressure.
(b) What is Bernoulli’s principle?
Ans. Bernoulli’s principle is that the pressure of air decreases when its velocity increases, while the pressure of air increases when its velocity decreases.
(c) Write the properties of air.
Ans. Air is a mixture of gases.
Air has mass and volume.
It spreads in all directions.
It exerts pressure.
It is colourless.
3. Give scientific reasons.
(a) When the piston of a syringe is released, it is immediately pushed in.
Ans. On pulling the piston of a syringe with the inlet hole of the syringe closed, more space becomes available to the air in the syringe, and it becomes rarified.
As a result, the pressure of the air in the syringe is lowered. Comparatively the pressure of the outside air is very high. So, when the pulled-out piston is released, it is immediately pushed in.
(b) Water droplets are seen on the outer surface of a glass having ice cubes in it.
Ans. Due to the ice cubes in the glass, the air surrounding the glass cools down. As the water vapour in this air cools down, it condenses and gets transformed into water. It is this water droplets that collects on the outer surface of the glass.
(c) Early morning dew drops are found on the grass.
Ans. During the dawn (early morning) when the temperature of air is low, its capacity to hold the vapour is less. At such times, the excess vapour is transformed into water droplets and we call them as dew drops.
(d) During the afternoon we feel that the air is dry.
Ans. In the afternoon, when the temperature of the air is high, the capacity of the air to hold the moisture also increases. Then, compared to its full capacity to hold water the proportion of moisture in the air is less and we feel that the air is dry.
(e) Earth’s surface remains warm and suitable for the living world on the earth.
Ans. The earth receives energy from the sun. This energy is reflected by the earth in the form of heat. The constituents of air surrounding the earth, such as water vapour, carbon dioxide, absorb a part of this heat and give it to the other constituents of air. So the Earth’s surface remains warm and suitable for the living world on the earth.
(f) We can hear the whistle of a distant train clearly early in the morning in winter.
Ans. The density of air changes due to change in its temperature. In winter, temperature is low so the density of the air is more. So we can hear the whistle of a distant train clearly early in the morning in winter.
(g) Ice floats on water.
Ans. When water freezes means it transforms into the solid state therefore its volume increases. When volume increases its density decreases. Density of ice is less than the water, so ice floats on water.
(h) It is easier to swim in the sea than in a well or a lake.
Ans. Sea water is saline. It contains salt whereas it is not so in well or a lake water. Due to salts dissolved in sea water, density of sea water is more, so the swimmer will not sink. Hence, it is easier to swim in the sea than in a well or a lake.
(i) Sandy soil is less fertile.
Ans. Sandy soil is made up of large particles and these particles of sandy soil are made of the mineral called silicon dioxide. These particles do not dissolve in water therefore soil has very little capacity to supply nutrients, so sandy soil is less fertile.
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