In
physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...
, action at a distance is the concept that an object can be affected without being physically touched (as in
mechanical contact) by another object. That is, it is the non-local interaction of objects that are separated in space.
Non-contact force
A non-contact force is a force which acts on an object without coming physically in contact with it. The most familiar non-contact force is gravity, which confers weight. In contrast a contact force is a force which acts on an object coming physic ...
s is action at a distance affecting specifically an object's
motion
In physics, motion is the phenomenon in which an object changes its position with respect to time. Motion is mathematically described in terms of displacement, distance, velocity, acceleration, speed and frame of reference to an observer and mea ...
.
This term was used most often in the context of
early theories of gravity and
electromagnetism
In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of a ...
to describe how an object responds to the influence of distant objects. For example,
Coulomb's law
Coulomb's inverse-square law, or simply Coulomb's law, is an experimental law of physics that quantifies the amount of force between two stationary, electrically charged particles. The electric force between charged bodies at rest is conventiona ...
and
Newton's law of universal gravitation
Newton's law of universal gravitation is usually stated as that every particle attracts every other particle in the universe with a force that is proportional to the product of their masses and inversely proportional to the square of the distan ...
are such early theories.
More generally, "action at a distance" describes the failure of early
atomistic and
mechanistic theories which sought to reduce all physical interaction to