For
a system of particles, this result is a powerful way to solve
problems. The momentum of a system of particles is simply defined as the
sum of the momenta of each individual particle. When the total force on is zero, the rate of change of momentum is zero, which means that the momentum is constant. For a single particle this is interesting but not particularly useful.
For
a system of particles, this result is a powerful way to solve
problems. The momentum of a system of particles is simply defined as the
sum of the momenta of each individual particle.
The total force on the system is the sum of all the forces acting on each of the particles in the system. Application of the third law shows that only external forces matter: The total external force on the system is equal to the rate of change of the system momentum.
Now if the total external force on the system is zero, then momentum of the system is constant. In detail this means that the vector sum of all the momenta; of each particle in the system is constant. When this situation is observed, the momentum of the system is said to be conserved.