Center of Gravity: A point – within or outside the body – where the entire weight of the body can be assumed to act. • Center of Mass: A unique point in the body which is a function solely of distribution of Mass coincides with C.G. if gravity field is uniform and parallel. • Centroid: The term centroid is used when calculations concern a geometric shape only. If density is uniform throughout the body, the centroid coincides with the center of Mass. A point – where the entire AREA (VOLUME) of the body can be assumed to be concentrated.
First Moment of an Area about any centroidal axis MUST be ZERO. Principal of Moments: Sum of moments of all the forces about a point is equal to the moment of resultant about that point. Extension of Varignon Theorem to non-concurrent system. R.d = ∑ Fidi • SUM OF MOMENTS = • MOMENT OFSUM