0J

0J denotes zero joules, the SI unit of energy and work. The joule is defined as the work done when a force of one newton moves a point of application by one meter in the direction of the force; equivalently, one joule equals one kilogram meter squared per second squared (1 J = 1 kg·m^2/s^2).

In practical terms, 0 J means that no energy has been transferred or stored with respect to the referenced process. For kinetic energy, a body in motion has KE = 1/2 m v^2, so if the speed v is zero, the kinetic energy is 0 J. Potential energy is defined relative to a chosen reference point, so a system can have zero potential energy by convention even while other forms of energy are present.

Zero energy can arise in several contexts: a process in which no work is performed and no heat is exchanged; a state of an object with zero kinetic energy; or an energy reference where a baseline is set to zero. It is important to note that 0 J is not a statement about the total energy of a system in an absolute sense, but about a particular form of energy or a specific reference frame or measurement.

Overall, 0J is a useful shorthand for describing either the absence of energy in a given form or the choice of a zero-energy reference in calculations, rather than a universal description of all energy in a system. See also: joule, energy, work, kinetic energy, potential energy.