CENTRE

(1) of Gravity. See Gravry. (2) of Oscillation, point in a pendulum or oscillating body such that if the whole ma of the pendulum were concentrated there, the time of oscillation would remain unchanged. (3) of Percu ion. If a body be free to rotate about a given axis, and if it be struck in such a way that the blow does not produce pre ure on the axis, then the direction of the blow pa es through a point in the plane containing the axis and the centre of ma —this is known as the centre of percu ion; in respect to any axis it is the same point as the centre of oscillation.