| CONSERVATION OF LINEAR MOMENTUM Momentum, or the quantity of motion, is a function of the mass and velocity of an object. For momentum to be conserved in any given situation, all the forces acting on an object must be accounted for. The linear momentum of a particle of mass m moving with a velocity v is defined to be the product of the mass and velocity.
Law of conservation of linear momentum: Whenever two or more particles in an isolated system interact, the total momentum of the system remains constant. This law tells us that the total momentum of an isolated system at all times equals it's initial momentum.
Notice there is no statement concerning the nature of the forces acting on the particle of the system. The only requirement is that the force must be internal to the system. In the case of pool, there is frictional force involved. The frictional force stops the motion of balls. The total energy in the system is thus conserved.
where d is the displacement of the objects traveled, F is the frictional force caused by gravitational force ( Ff = mg ).
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