I need help understanding the priciple of conservation of linear momentum heres the definition. priciple of conservation linear momentum is when there is no net external force (what does net external force mean?) acting on a system (what system?)of particles the total momentum of the system is conserved. how does this law coincide with newtons 1st 2nd and 3rd law? p.s. could u please help me understand newtons 2nd law?