We will discuss about energy and forms of energy. Energy is the ability to do work. We need energy to run, to play or to push a chair. Thus, a labourer who runs a trolley, bullocks that plough or pull a cart, etc. have energy.
When an object has a capacity to do a work, we say that it has energy. A car needs energy to move, winds needs energy to make trees sway, a railway engine that pulls a train, a motor that rotates a fan, etc. needs energy. Energy is also required to change matter. Cooking food requires energy. Changing water to water vapour requires energy.
Energy is available in different forms. They are:
(i) When we fix a wooden stake in the ground or an iron peg in a wooden plank and strike it with a hammer, we see that the stake goes into the ground or the peg pierces into the plank. The moving hammer has energy which forces the stake to go into the ground or the peg into the plank. The energy possessed by the moving hammer is mechanical energy. When the string of a bow is stretched, placing an arrow in the middle of the string and then it is let free. The arrow goes away from the bow. The energy in the stretched string of the bow is mechanical energy.
The energy in a pressed spring is also mechanical energy. Trolley pushing labourer, cart pulling bullock, boat steering rudder, cycle pedalling legs, etc. too have mechanical energy.
(ii) We get the heat energy by burning fuel such as wood, gas or petrol. When a kettle having water is heated steam begins to come out from its spout after some time. If a whirling is placed in front of the steam, it begins to rotate. The escaping steam presses the blades of the whirling and it begins to rotate. The steam is formed due to heat. Heat changes water into steam. Thus the energy in the steam is conserved heat energy.
A steam engine runs a train due to conserved heat energy in the steam. In the engine of a car, bus or truck, petrol or diesel burns and produces heat energy. This heat energy is the force that moves the car, etc. We use heat energy to cook food, heat water, melt metals, etc. We also get heat energy from the sun. It is one of the prime sources of heat. The heat given by the sun-rays is called solar energy.
(iii) We use electricity to do certain types of work. There are many appliances in which electric current is passed to do a work. Thus electrical energy too is a form of energy. When electrical current is passed through the motor of an electric fan, it begins moving.
Electrical energy is used in so many ways. It is used to light our houses and operate machines, etc. In cities, there are thermal power houses and in hilly areas hydro-electric power stations. They produce electrical energy for us and it is used for heating and lighting and for running electrical gadgets such as computer, electrical motor, grinding machines, tube-wells, etc. work due to electrical energy. We press our clothes with an electric iron and warm our houses with a heater. Electric iron and heater work by electrical energy.
(iv) Light and sound are also different forms of energy. Plants use light energy of sunlight to make food.