A trackball that is used notably for pointing at objects on a screen of a computer system comprises a body that is intended to be fixed to a workstation, a sphere that is rotatable with respect to the body, a set of sensors that provide information relating to the relative position of the sphere with respect to the body, and braking means for braking the rotational movements of the sphere with respect to the body. The braking means comprise a friction ring that encircles the sphere. The ring extends mainly in a plane perpendicular to an axis of symmetry of the sphere. The ring is free to move translationally in the plane in which the ring extends.