Consider a free rod lying horizontically in the air. Gravity produces no torque around the center of mass. Now let the rod be attached to a hinge like of that one the picture. Now the hinge provides an upwards force on the left end of the rod, whilst there is a torque effectively acting at the center of mass, which will make it rotate downwards. Correct so far right? Now what I dont understand is this: Obviously the rod doesnt rotate about its center of mass. Yet as the hinge provides an upwards force on the left end equal to mg, m being the mass of the rod, there must be a torque about the center of mass, since we saw that the rod just lying horizontally in the air had no torque about the cm. So therefore: Why doesnt the rod rotate about the center of mass?