Free particle

In physics, objects (e.g. charge carriers ) that are not in a potential are referred to as free particles . Thus no force acts on the particle and one only has to work against its inertia in order to change its speed ; the speed remains constant when no work is done. Since the potentials usually reach infinitely far, in most cases they are approximations. In cases where this approximation is only marginally sufficient, one also speaks of quasi-free particles.

The opposite of a free particle is the bound state .

Examples

• A spacecraft far away from all celestial bodies ( gravitational potential )
• An electron far away from other charges ( Coulomb potential )
• The Drude theory for the description of electrons in metals treats the electrons as free particles (except for the additional assumption that the electrons do not leave the metal).
• A free neutron is a neutron outside of atomic nuclei ( strong interaction )