5th Standard Science Term-I
Energy
Mala was standing in the row for her morning school assembly. Suddenly she fainted and fell down. Her class teacher rushed to her, took her to the class room and gave her water to drink. She came to know that Mala had skipped her breakfast. She was given some food and then she come back to normal. What do you understand from this?
We need energy to do our daily activities. We get this energy from the food. In science, energy is defined as the capacity to do work. Let us study about different forms of energy and their uses in this lesson.
We do many works in our daily life. Many of them are done physically. Some works are done with the help of instruments and devices. But, they also need energy to work. There are different forms of energy like mechanical energy, heat energy, light energy, wind energy and so on. Let us study about them here.
Energy possessed by an object due to its motion and position is called mechanical energy. Mechanical energy can be classified into two.
➜ Kinetic Energy
➜ Potential Energy
Kinetic Energy
Energy possessed by a moving object is known as kinetic energy. It is also known as energy of motion.
Examples : Moving car, cricket ball bowled by a player, bullet coming out of a gun.
Potential Energy
Energy possessed by an object which is at rest is known as potential energy. It is also known as stored energy of position.
Examples : Object lifted above, stone in the stretched rubber, water in the dam.
Uses of Mechanical Energy
Mechanical energy can be used to do many works. Some of them are given below.
➜ In hydro electric plants, kinetic energy of water is converted into electrical energy.
➜ Wind mills convert kinetic energy of winds into electrical energy.
➜ Mechanical energy of the hammer is used to apply force on the nail.
➜ Mechanical energy can bring a moving body to rest and make a body at rest to move.
Energy possessed by the wind is known as wind energy.
Uses of Wind Energy
➜ Wind mills use wind energy to generate electricity.
➜ Ships sail by the power of wind.
➜ Sports like wind surfing, sailing, kite surfing use wind energy.
➜ Wind energy can be used for pumping water.
When the temperature of substance is raised, its atoms and molecules being to vibrate and release a kind of energy. This energy is known as heat energy or thermal energy. This energy flows from a hot substance to a cold substance.
If was put some ice cubes into water in a glass, water becomes cold. It is because, heat is transferred from water to ice.
In both the cases, you can feel the heat. Thus, heat is produced by friction and chemical reactions also. Sun is the primary source of heat energy.
Uses of Heat Energy
➜ Heat energy obtained from power stations is used to generate electricity.
➜ Heat energy obtained from petrol and diesel is used to run vehicles.
➜ We cook food with the help of heat. Heat energy renders the food material soft and easy to digest.
➜ Hard substances like iron are heated to mould them into different shapes.
➜ Heat is used to dry clothes and other wet substances.
Light is a form of energy which travels as a wave. It contains a particle called photon which are the minute pockets of energy. It is the only form of energy visible to human eye. Light does not require any medium to travel. It travels at a speed of 3,00,000 km/s. Sunlight takes 8 minutes and 20 seconds to reach the earth.
Uses of Light Energy
➜ We are able to see objects with the help of light energy.
➜ Plants use light energy to synthesis their food.
➜ With the help of light energy, our skin is able to synthesis Vitamin-D.
➜ Electricity can be produced with the help of light energy.
We know that all things are made up of atoms. Atoms possess particles like protons, electrons and neutrons. Movements of electron in the objects causes an energy. This energy is called electrical energy. In our daily life we use batteries to get electrical energy. Electrical energy is also generated from nuclear power plants, hydroelectric plants and wind mills. It is also generated from solar energy.
Use of Electrical Energy
➜ Electrical energy is needed for the working of fan, light, television, washing machine, refrigerator etc.
➜ Electric iron box, electric stove and electric water heater work by electrical energy.
➜ It is used to run cars and trains.
➜ It is used in factories to produce materials.
Chemical energy is stored in substances when atoms oin together to form chemical compounds. When two or more chemical substances react with each other, this energy is released.
Use of Chemical Energy
➜ The food we eat contains chemical energy.
➜ Chemical energy in wood provides heat energy which helps us to cook food.
➜ Chemical energy in coal is used to generate electricity.
➜ Batteries we use in our daily life contain chemical energy.
➜ Fuels like petrol and diesel possess chemical energy which is used to run vehicles.
Energy cannot be created and it cannot be destroyed also. It is changed from one form to another form or transferred from one object to another object. We can say many examples for conservation of energy in our daily life.
Water stored in water dams possesses potential energy. When water falls down, potential energy of water is converted into kinetic energy. Kinetic energy of water rotates the turbines and electric energy is generated.
Electrical energy is used in many domestic appliances such as electric stove, iron box and fan. As current flows into the coil of the electric devices, it heats up the coil. With the help of this heat energy, we do many useful works. Thus, electrical energy is converted into heat energy. Electrical energy is converted to mechanical energy in fan, light energy in bulb and, sound and light energy in computer.
We use fuel in the form of petrol or diesel or gas to run vehicles. When this fuel burns in the engine, chemical energy is converted into heat energy. Burning fuel produces hot gases which pushes the piston in the engine to move the vehicle. Thus, heat energy is converted into mechanical energy.
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