The law of conservation of momentum states that the total momentum of a system before an event will be equal to the total momentum of the system after the event. That is, the total momentum of a system always remains the same.
In the equation,
[tex]P_1+P_2=P^{\prime}_1+P^{\prime}_2^{}_{}[/tex]If P₁ represents the momentum of object 1 before the event (say, collision) and P₂ represents the momentum of object 2 before the event. Then, P'₁ and P'₂ will represent the momentum of object 1 and object 2, respectively, after the event.