Centre of Gravity

(Phy.) Into whatever position a body may be turned with respect to the earth, there is a certain point, invariably situated with respect to the body, through which the resultant of the attracting forces between the earth and its several molecules always pa es. This point is called the C. of G.; it may be within or without the body, according to the form of the latter. To find the C. of G. of a body is a purely geometrical problem; in many cases, however, it can be determined immediately. For instance, the C. of G. of a right line of uniform density is the point which bisects its length; in the circle and sphere it coincides with the geometrical centre; in cylindrical bars it is the middle point of the axis. In order to determine experimentally the C. ofG. of a body, it is suspended D B ' Fig. 153. bya string in two different positions, as shown in Fig. 153; the point where the directions AB and CD of the string, in the two experiments, intersect each other is the C. ofG. required. For the resultant of the earth's attraction being a vertical force applied at the C. ofG., the body can only be in equilibrium when this point lies vertically under the point of suspension, that is, in the prolongation of the suspended string. But the C. of G. being in A B as well as inCD, must coincide with the point of intersection of these two lines, or D. [s. 159]