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"content": "Ryan and his friends are excited about their first day in Class 5. The Science teacher, Mr Khan, enters the class and introduces himself. He asks the students what they want to learn today. all students are curious to learn if there is something more precious than the gold after solving their ‘Icebreaker’ riddle. They ask Mr Khan about the same. He then starts explaining about ‘Rocks and inerals’.Rocks are made up of minerals. Minerals are natural non-living substances present in different quantities, qualities and arrangements within rocks.A rock may be made up of one or more minerals. Rocks are, thus, categorised into three groups – igneous, sedimentary and metamorphic rocks. Igneous rocks are formed by the cooling and hardening of hot liquid rock material, called magma. Magma is found in the underground pockets of the Earth. This magma is pushed upwards by the pressure of other rocks around it. Some of the magma cools and hardens below the Earth’s surface, while some flows out on the Earth’s surface and then hardens to form igneous rocks. Igneous rocks are found at the base of all landforms, such as plains, mountains, plateaus and ocean beds. Among all the landforms, rocks found in plateaus are usually rich in minerals (we will learn about minerals in the upcoming section). The type of igneous rock formed depends on the type of mineral that is present in magma and the size of the mineral particle.Sedimentary rocks cover the major portion of the Earth’s surface. These rocks are formed from pebbles, sand, mud, rocks or clay, deposited in the ocean and brought to the shore by lowing water or floating ice. Once on the shore, these materials pile up on each other and form different layers. The different layers are then cemented together by minerals. Some sedimentary rocks are formed by the shells of tiny sea creatures and some are formed from dissolved minerals that settle by ocean sides.Metamorphic rocks form by transformation of already existing rocks through a process called metamorphism. Most metamorphic rocks were once either igneous or sedimentary rocks. These rocks came under tons of pressure that led to heat build up, and finally, underwent metamorphosis.In some rocks, the minerals are broken down into smaller particles, whereas in others the minerals are stretched into flat particles.We already know that rocks are made up of minerals. These minerals can be either metallic or non-metallic in nature. Metallic minerals are used to obtain metals. The minerals from which metals can be profitably obtained are called ores. For example, haematite, bauxite, calamine and pyrite are some ores. We get iron, aluminium, zinc and copper,respectively, from these ores. These metals are generally used to make furniture, coins, machines, utensils and so on. Metals, such as gold, platinum and silver, are some precious metals that are used to make jewellery. Fossil fuels, such as coal and petroleum, are valuable resources that are found underground. They play a crucial role in providing energy supply. Coal is one of the most valuable mineral found under the Earth’s surface. It was formed thousands of years ago, when the land was low-lying and covered with thick swampy forest. As the plants died, they fell into the swamp and started to decay. The extreme pressure of the new vegetation over the dead plants at the bottom converted the vegetable matter to peat, lignite and coal. Coal is generally extracted from coal mines. In India, these coal mines are situated in Singrauli (Madhya Pradesh), Talcher (Odisha), Neyveli (Tamil Nadu), Raniganj (West Bengal) and Singareni (Telangana). Coal is generally used as fuel for cooking, heating homes and buildings, producing electricity in power plants, and in the steel industry for blast furnaces. Petroleum is another fossil fuel that provides half of the energy in the entire world. Petroleum is also known as black gold, liquid sunlight or rock oil. It is formed from remains of the dead plants and sea creatures that were buried millions of years ago in layers and gradually changed into oil and gas. In India, petroleum is obtained from Digboi (Assam), Ankleshwar (Gujarat) and Mumbai High, off the Mumbai coast.Petroleum is mainly used as fuel in different forms. Some of its other uses are in dry cleaning, printing ink, medicines and lubricating oil. Paraffin wax, obtained from petroleum, is used to make polish, candles and waterproof cartons. The increase in population has resulted in increased consumption of the natural resources.We must adopt steps to conserve natural resources so that they are available to our future generations as well. We should use coal, oil and petrol wisely. We can substitute them with inexhaustible natural resources, such as water, air and the Sun."
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"content": "We read about the different types of force in the previous class. Let us now learn more about force and energy. A force is a push or pull that when applied on any object tends to change the state, speed, direction and shape of the object. Muscular force: This force comes into play when we use muscles of our body to push or pull something. Some examples of muscular force are running, walking and bending. To apply this force, our body needs to be in contact with the surface of the other object. Hence, muscular force is a type of contact force. Gravitational force: Every object in this universe attracts other objects with a force known as gravitational force. When two bodies with some mass come closer to each other, they pull and attract each other. Gravitational force is always an attractive force. We are able to stand, walk, sit and be on the Earth’s surface due to the gravitational force exerted by the Earth on our body. Frictional force: It is the force that opposes the motion of an object moving on a surface. When a body moves on any surface, the surface exerts a force in the direction opposite to the motion of the object. This eventually stops the object. Some examples of frictional force are skating and driving a vehicle on the road. In addition to this, this force makes walking on the plains easier than on rocky mountains. Mechanical force: It is a contact force that acts between two bodies. A body that applies force on another tends to change the state of another one. Some examples of mechanical force include bending of a nail using pliers and drilling a hole into wood through a hand drill. Buoyant force or upthrust: When any object floating on water is pushed down, the water exerts an upward push on the object. This upward push is called upthrust. Human beings experience this force while entering a swimming pool. The ability to do work is called energy. Work is done when a force is able to produce movement in an object. Mechanical energy: It is the energy attained by the bodies on which work is being done. Mechanical energy is of two types – kinetic and potential. A body or an object has kinetic energy when it is in motion. A body or an object has potential energy when it is in stationary position. Solar energy: It is the form of energy obtained from the Sun. It is a renewable source of energy and does not cause any pollution to the environment.Geothermal energy: It is the energy that is derived from within the Earth. The hot water and steam generated within the Earth are used to produce electricity. Wind energy: It is the energy produced by moving air or wind. The kinetic energy of wind is converted into mechanical energy using wind turbines. The mechanical energy can further be transformed into electricity with the help of generators. Chemical energy: It is produced when different substances react with each other to form new substances. Electrochemical energy: It is the energy that is stored in batteries. Heat is an energy that is transferred from one body to another due to difference in temperature of the two bodies. Light is another form of energy that travels in straight lines pointed away from the source towards the viewer. Sound is also a form of energy produced due to the vibrations of different bodies. Electrical energy is generated due to the movement of electrical charges. As per this law, we cannot create or destroy energy. It can only be transferred from one form to another. The total energy of an object always remains the same."
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