Energy is a scalar physical quantity that represents the capacity to perform work or produce change. It exists in various forms, including kinetic energy (the energy of motion), potential energy (stored energy based on position), thermal energy (associated with temperature), chemical energy (stored in bonds of chemical compounds), and nuclear energy (released during nuclear reactions). Energy can be transformed from one form to another but cannot be created or destroyed, as stated by the law of conservation of energy. It is typically measured in joules (J) in the International System of Units (SI). Energy plays a crucial role in all physical processes in nature and is essential for powering biological systems, mechanical devices, and electrical systems.