CENTRE OF GRAVITY, CENTROID & MOMENT OF INERTIA
In this course we will learn about Centre of Gravity, Centroid & Moment of Inertia.
Centre of gravity and moment of inertia are two important properties of a body required in the study of the motion of rigid bodies. The Centre of gravity can be defined as the point through which the resultant force of gravity (weight ) of the body acts.
Centroid: The term centroid is similar to the centre of gravity. The term centre of gravity applies to bodies with mass and weight, and centroid applies to plane areas. ( 2d figures ). Centroid is a point in a plane area such that the moment of area about any axis through that point is zero.
“ It is a single point about which entire area is acting for a lamina or plane figure irrespective of the position of the plane figure.”
It is applicable to plane figures having areas but “no volume.”
CENTROID OF COMPOSITE SECTIONS
In engineering practice, use of sections which are built up with many simple sections are very common. Such sections may be called built-up sections or composite sections. To locate the centroid of composite sections, we have to split this section into suitable simple figures and then the centroid of each simple figure can be found by inspection or using the standard formulae.
Assuming the area of the simple figures as concentrated at its centroid, its moment about an axis can be found by multiplying the area with the distance of its centroid from the reference axis. After determining the moment of each area about reference axis, the distance of the centroid from the axis is obtained by dividing total moment of the area by the total area of the composite section.
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