Energy is defined as the capacity or ability to do work such as moving an object against a force, like frictional force. There are two main type of energy that are:
Potential energy , it is denoted with symbol U. It is a stored energy or energy which is due to it's position. For example, energy stored in a ball when it is taken to the building top.
Kinetic energy, it is denoted as K.E. . It is the energy that an object posses due to it's motion. For example, collision of pool balls.
