Im reviewing statics and came across this problem. There is a beam pin connected at one end and roller connected on the other. There is a moment at the pin and a force somewhere along the beam. Then they section it to find the internal normal shear and moment. One of the things i found slightly contraditory was that the moment can act anywhere along the beam. It causes the whole beam to rotate. But when the section the end where the roller is, they have to leave off the moment. This makes sense, I understand what there doing. The contradition seems to be that this end does not see the moment cuase where the pin is. Yet at the same time the moment at the pin causes the entire beam to rotate.