Some of the main sources from where we get energy are as follows.
1. The Sun: The Sum is our main source of energy. It gives us heat and light energy. Plants use the light energy of the Sun to make food for all living things. When we eat this food we get energy to work. So we are dependent on the Sun for our energy needs.
2. Moving water and air: Moving water and air have energy. This energy is mostly used to generate electricity.
3. Fuels: Fuels such as coal, oil, gas or petrol are excellent sources of energy. They have energy stored in them. This energy can be released by burning them. It is used to run machines, cars, heating homes, cooking and for many other things. However, burning of fuels also pollutes the air.
Consider some of the following situation:
(i) A labourer drives a trolley. Boys run. Children play a game. Swimmers swim in a pool or river. Singers sing a song. Dancers dance. In making these activities, fatigue is felt. All these actions need energy. We get the energy to do work and to overcome fatigue is received from food. Thus the food we take is the source of our energy. Due to our food we perform physical labour and mechanical work. So we should take proper food to do physical work.
(ii) We use wood, coal cooking gas etc. to obtain heat energy. We use petrol or diesel in our car, buses, scooter, trucks etc. to get heat energy. This heat energy is converted into mechanical energy to drive them. Thus fuels like wood, coal, petrol, diesel etc. are sources of heat energy.
(iii) Moving water and wind are also sources of energy. Hydroelectric power houses are the examples of production of hydroelectric energy from water. Water mills work by throwing water on its heels with force. Wind mills work due to blowing winds. Thus, water and wind become sources of mechanical energy.
(iv) Now-a-days the Sun is our main source of energy. We directly get solar energy from the Sun. There are many appliances such as solar-cooker, solar-heater etc. which are run by the solar-energy. Due to heat from the Sun water is evaporated and clouds are formed and thus it rains.
Plants grow. They provide us wood and coal. Wood and dead trees are buried deep under the ground. After a very long time they are converted into coal and petroleum. They are used as fuel to obtain heat energy.
Water, wood, coal, petroleum etc. are our important sources of energy. These are actually the products of the solar energy. Thus the sun provides us energy both directly and indirectly.