Every object has mass. When an object moves, it gains momentum; hence, momentum can be defined as mass in motion. The momentum of an object is dependent on two variables: its mass and its velocity. In terms of an equation, the momentum of an object is equal to the product of its mass and its velocity. It can be written as—

**p = m ****•** v

wherein *p* is the momentum, *m *is the mass, and *v *is the velocity of the object.

One of the most important laws in physics is the Law of Conservation of Momentum. This law corresponds with Newton’s Law of Action and Reaction, which states, “For every action, there is an equal and opposite reaction.” We usually associate the Law of Conservation of Momentum with colliding objects; hence, it can be stated, “In an isolated or a closed system (no external force in the system), the total momentum of two colliding objects before the collision is equal to the total momentum of the two objects after collision.” This tells us that the momentum in an isolated or a closed system is conserved.

As an equation, the Law of Conservation of Momentum can be expressed as—

${\mathit{T}}{\mathit{o}}{\mathit{t}}{\mathit{a}}{\mathit{l}}{\mathbf{}}{{\mathit{p}}}_{\mathbf{i}\mathbf{n}\mathbf{i}\mathbf{t}\mathbf{i}\mathbf{a}\mathbf{l}\mathbf{}}{\mathbf{=}}{\mathbf{}}{Total{p}_{\mathrm{fina}l}}$

wherein ρ initial is the initial momentum and ρ final is the final momentum of the objects in the system. Knowing the equation for momentum, the equation for Law of Conservation of Momentum can also be written as—

${{\mathit{m}}}_{\mathbf{1}}{\mathbf{}}{\mathbf{\u2022}}{\mathbf{}}{{\mathit{v}}}_{\mathbf{1}\mathbf{}\mathbf{\left(}\mathbf{i}\mathbf{n}\mathbf{i}\mathbf{t}\mathbf{i}\mathbf{a}\mathbf{l}\mathbf{\right)}\mathbf{}\mathbf{}\mathbf{}}{\mathbf{+}}{\mathbf{}}{{\mathit{m}}}_{\mathbf{2}}{\mathbf{}}{\mathbf{\u2022}}{\mathbf{}}{{\mathit{v}}}_{\mathbf{2}\mathbf{}\mathbf{\left(}\mathbf{i}\mathbf{n}\mathbf{i}\mathbf{t}\mathbf{i}\mathbf{a}\mathbf{l}\mathbf{\right)}\mathbf{}}{\mathbf{}}{\mathbf{=}}{{\mathit{m}}}_{\mathbf{1}}{\mathbf{}}{\mathbf{\u2022}}{\mathbf{}}{{\mathit{v}}}_{\mathbf{1}\mathbf{}\mathbf{\left(}\mathbf{f}\mathbf{i}\mathbf{n}\mathbf{a}\mathbf{l}\mathbf{\right)}\mathbf{}\mathbf{}\mathbf{}}{\mathbf{+}}{\mathbf{}}{{\mathit{m}}}_{\mathbf{2}}{\mathbf{}}{\mathbf{\u2022}}{\mathbf{}}{{\mathit{v}}}_{\mathbf{2}\mathbf{}\mathbf{\left(}\mathbf{f}\mathbf{i}\mathbf{n}\mathbf{a}\mathbf{l}\mathbf{\right)}\mathbf{}}$

Watch the videos of real-life application of the Law of Conservation of Momentum.