▁Let ▁the ▁system ▁of ▁particles ▁Pi , ▁i = 1 ,..., n ▁of ▁masses ▁mi ▁be ▁located ▁at ▁the ▁coordinates ▁ri ▁with ▁veloc ities ▁vi . ▁ ▁Select ▁a ▁reference ▁point ▁R ▁and ▁compute ▁the ▁relative ▁position ▁and ▁velocity ▁vectors , ▁ ▁The ▁total ▁linear ▁and ▁angular ▁momentum ▁vectors ▁relative ▁to ▁the ▁reference ▁point ▁R ▁are ▁ ▁and ▁ ▁If ▁R ▁is ▁chosen ▁as ▁the ▁center ▁of ▁mass ▁these ▁equations ▁simplify ▁to ▁ ▁where ▁m ▁is ▁the ▁total ▁mass ▁of ▁all ▁the ▁particles , ▁p ▁is ▁the ▁linear ▁momentum , ▁and ▁L ▁is ▁the ▁angular ▁momentum ▁ ▁The ▁Law ▁of ▁Conserv ation ▁of ▁M oment um ▁predict s ▁that ▁for ▁any ▁system ▁not ▁subject ed ▁to ▁external ▁forces ▁the ▁momentum ▁of ▁the ▁system ▁will ▁remain ▁constant , ▁which ▁means ▁the ▁center ▁of ▁mass ▁will ▁move ▁with ▁constant ▁velocity . ▁ ▁This ▁applies ▁for ▁all ▁systems ▁with ▁classical ▁internal ▁forces , ▁including ▁magnetic ▁fields , ▁electric ▁fields , ▁chemical ▁re actions , ▁and ▁so ▁on . ▁ ▁More ▁formally , ▁this ▁is ▁true ▁for ▁any ▁internal ▁forces ▁that ▁cancel ▁in ▁accord ance ▁with ▁Newton ' s ▁Third ▁Law . ▁ ▁Loc ating ▁the ▁center ▁of ▁mass ▁ ▁The ▁experimental ▁determ ination ▁of ▁the ▁center ▁of ▁mass ▁of ▁a ▁body ▁uses ▁gravity ▁forces ▁on ▁the ▁body ▁and ▁re lies ▁on ▁the ▁fact ▁that ▁in ▁the ▁parallel ▁gravity ▁field ▁near ▁the ▁surface ▁of ▁the ▁earth ▁the ▁center ▁of ▁mass ▁is ▁the ▁same ▁as ▁the ▁center ▁of ▁gravity . ▁ ▁The ▁center ▁of ▁mass ▁of ▁a ▁body