To be able to describe the motion of rigid bodies by applying the conservation of linear and angular momenta. If the sum of all the linear impulses acting on a system of connected rigid bodies is zero, the linear momentum of the system is conserved. Mathematically, this relationship is expressed as (∑syst. linearmomentum)1=(∑syst. linearmomentum)2 and is called the conservation of linear momentum. If the sum of all the angular impulses (created by the external forces that act on the system) is negligible or zero, then the angular momentum of a system of connected rigid bodies is conserved about the system's center of mass or about a fixed point. Mathematically, this relationship is expressed as (∑syst. angularmomentum)1=(∑syst. angularmomentum)2 and is called the conservation of angular momentum.