Physics is the study of matter, energy and the interplay of matter and energy. Energy is an important concept in physics because it is all around us and shaping our lives. Without energy no useful work can be done. Energy is an all-pervading concept which finds many uses in its many forms.
Energy can be expressed in various systems of units but its standard adopted unit is that of a joule. When you shift a rock by a distance of one meter while applying a force of one newton on it, then you will have expended one joule of energy in doing the work. In order to perform our day-to-day activities we need energy and we get that energy from the carbohydrates in our meal. That’s why you are advised to include more carbohydrates in your diet when you exercise rigorously in gym so that you can continue to lift those heavy weights and do some work in building your muscles.
Various forms of energy
Energy is present in nature in various forms. The most common source of energy for Earth is the sun. The sun provides us with light energy and heat energy. Coal has chemical energy which is converted into heat energy when it is burned and this heat energy is used to boil water to produce steam and rotate turbines for the production of electrical energy. A moving ball has kinetic energy. When you raise a mullet to hammer the landing at the base of a High Striker in a carnival, it gains potential energy. And this potential energy is used to do useful work in the form of hitting the bell at the top of the tower.
Transformation of energy
As you can understand, energy always transforms from one form to another but it never simply vanishes. This is because of the law of conservation of energy which states that energy can neither be created nor destroyed but it can only be transformed from one form to the other. Where does the kinetic energy go when you roll a ball on the ground and it comes to a halt? There is a force called friction which works on the surface of the ball. This friction force opposes the rolling of the ball and dissipates the kinetic energy in the form of heat. The heat is taken up by the ball, ground and surrounding air with a small, insignificant rise in their temperatures.
Energy is work and heat
Let us take a container full of water and close it with a lid tightly so that nothing can be added or taken away from this system. Supply it with heat with the help of a Bunsen burner. In order to facilitate the heating and make it uniform, let us stir the water. This churning of water requires some work to be done at our end. If you now measure the energy of this system of container full of water and steam, it will be equal of the heat that we supplied to it and the churning work that we did on it. In case there was no heating, the energy of the system would simply be the churning work that was performed by us.