Potential Energy

Potential energy is energy that depends on the position or configuration of an object within a force field. For example, a stone lifted to a height possesses potential energy that depends on that height; when released, this energy converts to kinetic energy (energy of motion).

Potential energy can be defined only when the acting force is conservative—such as gravity, electrical force, or spring force. Forces like friction cannot be described in terms of potential energy, because the work they do depends on the path taken, not merely on the starting and ending points.

Definition and measurement

The change in potential energy equals the work done by a conservative force, with opposite sign. Therefore, the absolute value of potential energy is not fixed: it is measured relative to a reference level chosen by the observer. Only the difference between two states is meaningful. The unit of measurement is the joule (J).

Common types

Gravitational potential energy near Earth's surface is calculated as m·g·h, where m is mass in kilograms, g is the acceleration due to gravity, and h is height measured from a reference level. Elastic potential energy depends on how far a spring or elastic material is stretched or compressed. There is also electrical potential energy between charged particles, chemical potential energy stored in atomic bonds, and nuclear potential energy within the nucleus.

Conservation of energy

When no dissipative forces act, the sum of potential and kinetic energy remains constant—this is called mechanical energy conservation. If friction or air resistance is present, some energy converts to heat, reducing the total mechanical energy, although the total energy of the system is not destroyed.

Applications

The concept of potential energy is used in calculating body motion, in designing hydroelectric systems (where water height is converted to electricity), and in storing energy economically through systems such as elevated water reservoirs. Chemistry and biology explain how energy stored in food bonds is used to do work in the body.