**Description**: Laplace force acting on a conducting bar in rectilinear translation on two parallel rails (Laplace rails) in a uniform external magnetic field, stationary and orthogonal to the bar. Know the expression of the resultant of Laplace forces in the case of a conducting bar placed in a uniform and stationary external magnetic field. (Laplace force = result of all Lorentz forces undergone by charged particles in motion in an electromagnetic field.)

**Definitions**

__Lorentz force__: the force which is exerted by a magnetic field on a moving **electric charge**.

__Laplace force__: the force applied on a **conductor** traversed by an electric current, in a magnetic field.