Percussion Centre of, in any body or system of bodies revolving about a point or axis, is that point which, striking an immovable object, the whole mass shall not incline to either side, but rest in equilibrio without acting on the centre of suspension. If a person attempt to strike any object with a straight stick, and do not strike it in the centre of percussion, a considerable jarring will occur, which will not be felt if the blow be given in that point. In a straight stick of equal thickness, the centre of percussion is two-thirds of the length of the stick from the axis of motion. Generally, the distance of the centre of percussion from the centre of motion is equal to the sum of the products of each particle of the body, by the square of its distance, divided by the product of the whole mass by the distance of its centre of gravity from the axis of motion.