Hello there! I am currently studying the equilibrium of rigid body and encountering a doubt. Now, in their explanation of reaction forces by a roller or a rocker or a smooth surface, they generalize it as in the preceding examples prevent the translation of a beam for example in ONE direction only whereas a smooth pin or hinge or a rough surface prevent translation of the beam in ANY direction, thus there are two components of the force. How is it so? I can understand that a roller cannot prevent the beam from moving upwards for instance but at least in can prevent the beam from penetrating the surface downwards in any direction.