The Fundamentals of Energy
Most fundamentally, energy is the ability of an object or a system to perform work, and we most often observe energy indirectly by the work that is performed. The motion of an object through space, the heating of a substance and the illumination of a room are all examples of work being done and represent different forms of energy.
By the laws of thermodynamics, energy can never be created or destroyed, and so when people talk about "generating" energy in a power plant or by using photovoltaic modules, they are actually referring to the transformation of energy from one form into a more useful form.
Potential energy is the energy of a system due to the position of its components. Potential energy is essentially stored in an object or a group of objects because of their condition. A stretched spring is poised to compress as soon as it's released, and the tension in the spring therefore represents potential energy. Similarly, an object held at a distance above the ground will begin to fall as soon as it's released, and therefore its condition represents the potential for motion. These are both examples of potential energy; each system is still, but is positioned to do work once permitted. Potential energy can also be found stored chemically in a substance or in the bonds between particles in the nucleus of an atom.
Forms of Potential Energy
Chemical potential energy is the energy stored in chemical bonds. In essence, it is the potential of a substance to undergo a transformation through a chemical reaction. An example of this is the burning of a fuel. The chemical energy stored in the fuel is transformed into thermal energy through combustion.
Elastic potential energy is the energy of an elastic object, such as a rubber band or spring, under tension. A slingshot is an excellent example of elastic energy: as soon as tension is released, the elastic energy of the system is transformed into kinetic energy, propelling the object from the slingshot through the air.
Electric potential energy is the energy of an object or a system due to electric charge. A charge will exert a force on any other charge, and this force represents the potential to perform work. For instance, a positively charged particle will exert an attractive force on a negatively charged particle in its vicinity. If these two charges are held stationary, electrical potential energy will continue to exist between them. When dealing with electricity, it's generally convenient to deal with electric potential energy per unit of charge, simply "electric potential." The difference in electrical potential between two places in space is known as voltage.
Gravitational potential energy is the energy possessed by an object because of the force of gravity acting upon it. An object held up some distance from the ground has gravitational potential energy. As soon as it's released, the force of gravity will cause the object to fall toward the earth.
Nuclear potential energy is the energy of the bonds between particles in the nucleus of an atom. It is possible to perceive the presence of this energy through the energy transformation that occurs when these bonds are created or destroyed. Nuclear fusion, which powers the Sun, and nuclear fission, which is used in nuclear power plants, are both examples of the transformation of nuclear potential energy into electromagnetic and thermal kinetic energy.
Kinetic energy is the energy of an object or system because of its motion. Kinetic energy dictates the amount of work a moving object or system is capable of doing on another system with which it comes into contact.
Forms of Kinetic Energy
What this section will describe as motion is the energy of a moving object in the most traditional sense. While all kinetic energy is that of motion, in this instance "motion" will be defined as the observable movement of an object in a system: for instance, the motion of a ball after it has been dropped.
Acoustic kinetic energy is energy that travels in longitudinal waves and that we experience as sound.
Electrical kinetic energy is the energy of flowing electrons. It is derived from electric potential energy, which causes electrons to flow. To give an example, the two terminals of a charged battery have different electrical potential energies or - in other words - a voltage between them. If permitted, the energy in a system will tend to equalize, moving from a state of higher potential to that of a lower potential. Therefore, once the terminals of the battery are connected, electrical charge will begin to flow from one terminal to the other. The rate of at which electrical charge flows due to the difference in electric potential energy between two places is known as electrical current.
Electromagnetic kinetic energy is energy that travels in transverse waves. Visible light is an example of electromagnetic energy, and the amount of energy in an electromagnetic wave is related to its wavelength and frequency.
Thermal kinetic energy is the energy of an object or system due to the internal movement or vibration of its atoms. We experience thermal energy as heat. The faster a substance's constituent atoms are moving, the higher its temperature.