MOMENT OF INERTIA

• 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 = ∑ Fi di

SUM OF MOMENTS = MOMENT OF SUM

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