The external forces represent the action of other bodies on the rigid body under consideration. Only external forces can impart to the rigid body motion of translation or rotation or both. Imagine a two-body system of masses under a classical mechanics model. The separation and mass-ratio don't matter for this example. Presume they are initially stationary.
Related journals of External Force
Industrial Engineering & Management, Aeronautics & Aerospace Engineering, Applied Mechanical Engineering, International Journal of Advancements in Technology The Journal of Physiology, The Journal of Physical Chemistry, Journal of Biomechanics, International Journal of Humanoid Robotics, Brazilian Journal of Physics