Nonconservative force

A force whose work between two positions depends on the path taken. Its work around a closed path is nonzero, so it cannot be represented by a single-valued potential energy.

Work (physics): The energy transferred when a force acts through a displacement. Nonconservative work varies with the route taken between the same endpoints.
Kinetic friction: The frictional force opposing the relative sliding of contacting surfaces. Its work depends on the sliding distance, not just the endpoints.
Vector field: A function assigning a vector to each point in space. A force is modeled as a vector field whose work can be tested along paths.
Electrostatic force: The force between electric charges at rest, described by Coulomb's law. In electrostatics this force is conservative, unlike forces with path-dependent work.
Line integral: An integral that accumulates a scalar or vector quantity along a curve. Work by a force is computed by integrating its component along the path.
Fluid drag: The resistive force exerted by a fluid on an object moving through it. Drag removes mechanical energy along the object's trajectory.
Closed path: A curve whose final point is the same as its initial point. Nonzero work around a closed path is a direct test of nonconservativeness.
Gravitational force: The attractive force between masses, described by Newton's law of gravitation in classical mechanics. In the usual static-field treatment, gravity is conservative and admits potential energy.
Conservative force: A force whose work between two positions is independent of the path. Its path independence marks the defining opposite of nonconservative behavior.
Rolling resistance: The resistive force opposing a wheel's motion over a surface. It dissipates energy through deformation and depends on motion along the route.

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