# Centre of Gravity | Definition, Importance – Rotational Motion

Centre of Gravity in Physics:
If a body is supported on a point such that total gravitational torque about this point is zero, then this point is called centre of gravity of the body.

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## Centre of Gravity | Definition, Importance – Rotational Motion

Centre of gravity coincides with centre of mass, if g is constant. But for large objects g will vary, hence centre of gravity does not coincide with centre of mass.

Importance of Centre of Gravity
1. Centre of gravity vastly simplifies calculations involving gravitation and dynamics to be able to treat the mass of an object as if it is concentrated at one point.

2. The center of gravity is based on weight, whereas the center of mass is based on mass. So, when the gravitational field across an object is uniform, the two are identical. However, when the object enters a spatially-varying gravitational field, the COG will move closer to regions of the object in a stronger field, whereas the COM is unmoved.

Rotational Motion:
In this portion, we will learn about the rotational motion of the objects. A body moves completely in rotational motion when each particle of the body moves in a circle about a single line. When a force is applied on a body about an axis it causes a rotational motion. The force applied here is called the torque. The axis of the rotation usually goes through the body. Also, learn the two theorems such as parallel axes and perpendicular theorem explained with respect to rotational motion of objects.