What is energy? It is the capacity to do work. The quantity of work you can do depends on the amount of energy. Let's find energy around you at this moment. As you may be looking at a computer screen now, you may be using electrical energy. Your hand clicking on the mouse is using kinetic energy. If your home is heated with gas, it is using fossil energy. If you are eating a snack, you are consuming food energy. I have not talked about the most basic energy yet: The most powerful and abundant energy on Earth, and the energy that causes seasonal changes, creates day, and supports all living things; it is the energy from the sun.

Some energies are not related to solar energy, which include potential energy generated by gravity and nuclear energy held in particles of atomic nuclei. However, it is no exaggeration to say that most of the energy we use is solar energy. The food energy that is essential for our survival begins with photosynthesis of plants that store solar energy. Fossil energy such as petroleum and coal that generates electricity and operates industries can be said to have come from solar energy, because fossil fuels were formed from the remains of dead organisms that had lived on Earth a very long time ago. The sun is a star releasing tremendous heat and light energy. The heat radiation of the sun reaching Earth is absorbed and converted into thermal energy. Such energy that travels through space from high-temperature to low-temperature objects in the form of light is called radiant energy.

Energy can be converted but not lost.

Energy can change in different forms. The food energy from today’s breakfast is digested and stored in your body and used as kinetic energy when you run home after school. Fossil fuels are burned in a power plant to be converted into thermal energy, which becomes the kinetic energy that runs the generator; the generator produces electrical energy. However, even if 100 units of fossil energy have been used, electric energy is not produced in the same units. This is because energy is distributed in other forms while it is transformed. For example, the electrical energy of the engine of a solar car is not only fully used as kinetic energy to run the car; it is also used as sound energy when the vehicle runs making a bwaaah noise and as heat energy making the engine warm. When energy is converted, it can be dispersed into many different forms of energy. However, the sum of each energy - kinetic, heat, and sound energy - equals the total amount of energy before transformation. This is called the law of conservation of energy.

Source: Eco-generation Korean Website