Conservation of momentum

Momentum is always conserved. The momenta of individual objects in a system may vary, but the vector sum of all the momenta will not change. Therefore, momentum is said to be conserved.

The conservation of momentum in a glancing collision between two objects is expressed as $\left(M_{\mathrm {1} }V_{\mathrm {1i} }\right)+\left(M_{\mathrm {2} }V_{\mathrm {2i} }\right)=\left(M_{\mathrm {1} }V_{\mathrm {1f} }\right)+\left(M_{\mathrm {2} }V_{\mathrm {2f} }\right)$

The conservation of momentum in a collision between two objects where the two objects become one is expressed as $\left(M_{\mathrm {1} }V_{\mathrm {1i} }\right)+\left(M_{\mathrm {2} }V_{\mathrm {2i} }\right)=\left(M_{\mathrm {1} }+M_{\mathrm {2} }\right)V_{\mathrm {f} }$