If R is chosen as the center of mass these equations simplify to p = m v , L = ∑ ∑ i = 1 n m i ( r i − − R ) × × d d t ( r i − − R ) + ∑ ∑ i = 1 n m i R × × v where m is the total mass of all the particles, p is the linear momentum, and L is the angular momentum.