Why does a force applied exactly perpendicular to one end of a rigid rod produce translatory motion along with rotational motion about center of mass? I know the mathematics F=m(center of mass)*a but I want a mechanical answer. Please help me analyze the mechanics of it. I think analyzing the following thought experiment will be of some help though i don't know how to proceed with it. Consider two spherical bobs attached to two ends of an elastic string.(rigid rod as a limiting case of elasticity) When an exact perpendicular force is applied at one bob the bob will accelerate and move along a straight line while the other bob remains at rest. Now due to an increase in length of the string a tension will be developed and will pull both the bobs toward its center of mass. I don't know how to proceed with it and can't see why the rotation is about center of mass.