MOMENTUM (Lat., movement, particle sufficient to turn the scales, moment). or QUANTITY or MOTION, The product of the of a moving particle and its linear velocity. ( It is a vector quantity.) Both terms were used by Galileo; the latter by Newton. It is a fundamental principle of mechanics (q.v.) that the numerical value of the influenee of any external body in (-hanging the motion of a moving. particle is the rate of ehange of mo mentum with referiMee to the time. or the change in one second if the change is uniform. The total change of momentum in any time equals the 'impulse' of the external force, or the product of the force and the interval of time. If a bullet enters a target, the time required for it to come to rest depends upon its momentum but the distance it enters. upon its kinetic en ergy. Thus to produce a powerful blow a great momentum (mr) is required; but to do destruc tive damage. great kinetic energy ( f, . If
a system of bodies is moving free from external influence, the geometrical sum of the linear momenta of all the bodies of the system remains unchanged regardless of how the momenta of the individual bodies are altered by imparts, explosions. etc. This is called the 'principle of the conservation of linear momentum.' 1:3y geometrical sum is meant the proves, of adding geometrically the which indieate the mo menta of the individual bodies of the system.) If it rigid body is rotating about a fixed axis, the product of moment of inertia about this axis and its ammlar veloeity is called its 'angular momentum Carnal it plays the same part in motion of rotation that linear momentum does in trans lation. See It:CIIANIC'S.