Coined in the 19th century by the Scottish engineer and physicist William Rankine, the term ′potential energy′ denotes a set of forces acting upon a body at a specified point in space. It is measured in Joules, the SI unit of energy, which is work done or heat generated in an observed system. Work is the effect of a force applied to a body over a distance, creating motion in the direction of that force, and energy is the capacity within a system to carry out work.
A more formal definition is that potential energy is the difference between the energy of a body in motion, measured at a given point in its trajectory, and the energy level at a designated reference point. This is its zero point. For example the gravitational potential energy of a body is calibrated against ground level zero. The elastic potential energy is calibrated against a system′s state of equilibrium, or zero energy. Such a system is a set of vectors, also called a ′force field′, so that each measurement can be regarded as a freeze-frame of a body′s motion within the paradigm of the force field.
Elastic potential energy is the energy stored in a system due to stretching or compression. A spring is an example of such a system.
Electrical potential energy is the energy generated by the arrangement of charged points in a system. It is due to the intrinsic electrical charge of a body or its position relative to other bodies carrying an electrical charge.
Chemical potential energy is a function of the structural arrangement of atoms or molecules in a body or within a chemical reaction.
Nuclear potential energy is the strong nuclear force, which holds an atom′s nucleus together, binding protons and neutrons and in turn binding the quarks that create them; or it is the weak nuclear force, which is caused by the emission of bosons and is responsible for radioactive decay and nuclear fusion.
Gravitational potential energy is the energy stored in a body by dint of its position in relation to the earth, whose force of attraction, or gravitational pull, causes that body to fall.
Intermolecular potential energy is that force of attraction and repulsion acting between immediately nearby particles. These particles may be atoms, ions or molecules.