In a collision the momentum change of object 1 is equal to and opposite of the momentum change of object 2. Equation 2 is therefore equivalent to three scalars equations one for each coordinate direction. The linear momentum balance equation in terms of material stress follows directly by substituting into this equation for Sij in terms of Sij The angular momentum balance equation can be derived simply by substituting into the momentum balance equation in terms of Cauchy stress sij sji 55 Work done by Cauchy stresses.
Let us study more about Linear momentum and conservation of momentum.
It is a vector quantity and its direction is in the direction of velocity of the body. The equation expressing conservation of momentum is. Equation 2 is therefore equivalent to three scalars equations one for each coordinate direction. The Law of Momentum Conservation The above equation is one statement of the law of momentum conservation.