Scientists define energy as the ability to do work. Modern civilization is possible because people have learned how to change energy from one form to another and then use it to do work.

The reason it is so hard to define is because it’s an abstract notion. In physics, the concept of “energy” is really just a kind of shorthand, a tool to help balance the books. It is always conserved (or converted into mass) so is incredibly useful in working out the results of any kind of physical or chemical process. There is no physical “essence” of energy, and no such thing as “pure energy”. It is always carried by something, usually in the form of movement.

Energy comes in various forms—from sonic and gravitational to nuclear and thermal. Understanding these diverse forms of energy helps us comprehend the forces that fuel our natural world and day-to-day activities, from charging our cell phones to powering our homes.

The sun is the main source of energy on Earth. Other energy sources include coal, geothermal energy, wind energy, biomass, petrol, nuclear energy, and many more. Energy is classified into various types based on sustainability as renewable sources of energy and non-renewable sources of energy.

Renewable Energy, also called Alternative energy is any energy source that is an alternative to fossil fuel. These alternatives are intended to address concerns about fossil fuels, such as its high carbon dioxide emissions, an important factor in global warming. Marine energy, hydroelectric, wind, geothermal and solar power are all alternative sources of energy.

The Sun is he star around which the earth moves and that provides light and heat for the earth: The sun is the center of our solar system. Sun also means the light or heat that the earth receives from this star: Sit in the sun where it's a lot warmer. sun.

Science is the intellectual and practical activity encompassing the systematic study of the structure and behaviour of the physical and natural world through observation and experiment.