Php lut ca ma st kh Cc tnh cht c bn ca ma st trt (ng) c pht hin bi th nghim trong 15 n th k 18 v c th hin nh ba php lut thc nghim: Lut Amontons ' : Lc ma st trc tip t l thun vi ti trng p dng. Lut th hai Amontons: Lc ma st c lp ca khu vc lin h r rng ca. Lut ca ma st Coulomb: Kinetic ma st c lp ca vn tc trt . Lut 2 Amontons l mt s l tng ha gi nh vt liu hon ton cng nhc v khng n hi. V d, lp xe rng hn trn xe t cung cp lc ko nhiu hn so vi lp xe hp cho mt khi lng xe nht nh v s bin dng b mt ca lp [cn dn ngun] Kh ma st Ma st kh chng li chuyn ng bn tng i ca hai b mt cht rn tip xc. Hai ch ma st kh l ma st tnh gia cc b mt khng chuyn ng, v ma st ng (i khi c gi l trt ma st hoc ma st ng) gia cc b mt chuyn ng . Coulomb ma st, t theo tn ca Charles-Augustin de Coulomb, l mt m hnh gn ng c s dng tnh ton lc lng ca ma st kh. N b chi phi bi phng trnh: ni l lc ma st tc dng ca mi b mt khc. l song song vi b mt, tri ngc hng vi lc lng p dng net. l h s ma st, m l mt ti sn thc nghim ca cc thnh phn lin h, l lc lng bnh thng tc dng ca mi b mt vung gc vi hng dn, (bnh thng) b mt. Ma st Coulomb c th mt bt k gi tr t s khng ln n , V s ch o ca lc ma st chng li mt b mt i din s chuyn ng b mt s kinh nghim trong trng hp khng c ma st. Nh vy, trong trng hp tnh, lc ma st l chnh xc nhng g n phi c ngn chn chuyn ng gia cc b mt, cn bng lc lng rng c xu hng gy ra chuyn ng nh vy. Trong trng hp ny, ch khng phi l cung cp mt c tnh ca lc ma st thc t, xp x Coulomb cung cp mt gi tr ngng cho lc lng ny, trn m chuyn ng s bt u. Lc lng ti a ny c gi l lc ko . Lc ma st lun lun l tc dng trong mt hng chng li chuyn ng (i vi ma st ng) hoc chuyn ng tim nng (i vi ma st tnh) gia hai b mt. V d, mt un trt dc theo bng kinh nghim ng mt lc lng lm chm n xung. i vi mt v d v phong tro tim nng, cc bnh xe li xe ca mt chic xe tng tc kinh nghim mt lc ma st ch v pha trc, nu h khng, cc bnh xe quay, v cao su s trt v pha sau dc theo va h. Lu rng n khng phi l hng chuyn ng ca chic xe m h phn i, l s ch o ca (tim nng) trt gia lp xe v ng. Lc lng bnh thng Khi trn mt on ng ni (mi nht) v s c th tng ng ca khi (di) . Bi chi tit: lc lng bnh thng Lc lng bnh thng c nh ngha l lc lng tnh nn hai b mt song song vi nhau; v hng ca n l vung gc vi b mt. Trong trng hp n gin ca mt khi lng ngh ngi trn mt b mt nm ngang, cc thnh phn duy nht ca lc lng bnh thng l lc lng do lc hp dn, ni . Trong trng hp ny, ln ca lc ma st l sn phm ca khi lng ca i tng, tng tc do trng lc, v h s ma st. Tuy nhin, h s ma st khng phi l mt chc nng ca khi lng hoc th tch, n ch ph thuc vo vt liu. V d, mt khi nhm ln c cng h s ma st nh l mt khi nhm nh. Tuy nhin, ln ca lc ma st ph thuc vo lc lng bnh thng, v do khi lng ca khi. Nu mt i tng c trn mt b mt bng phng v lc lng c xu hng gy ra trt ngang, cc lc lng bnh thng gia cc i tng v b mt l trng lng ca n, l bng cakhi lng nhn vi gia tc do trng lc ca tri t , g. Nu i tng trn mt b mt nghing nh mt mt phng nghing, cc lc lng bnh thng l t hn, bi v t lc hp dn vung gc vi khun mt ca my bay. Do , lc lng bnh thng, v cui cng l lc ma st, c xc nh bng cch s dng vector phn tch, thng l thng qua mt s c th min ph. Ty thuc vo tnh hnh, vic tnh ton ca lc lng bnh thng c th bao gm cc lc lng khc hn so vi lc hp dn. H s ma st Cc h s ma st (COF), cng c bit n nh l mt "h s ma st" hay "h s ma st" v biu tng l ch ci Hy Lp , l mt gi tr v hng dimensionless trong m t t l ca lc ma st gia hai c quan, lc p chng li vi nhau. H s ma st ph thuc vo vt liu c s dng, v d, nc trn thp c h s ma st thp, trong khi cao su trn va h c mt h s ma st. H s ma st phm vi t gn bng khng ln hn mt trong nhng iu kin tt, mt lp xe trn b tng c th c mt h s ma st l 1,7 [ cn dn ngun ] i vi b mt phn cn li lin quan n nhau , Ni l h s ma st tnh. iu ny thng ln hn so vi ng ca n. i vi cc b mt chuyn ng tng i , Ni l h s ma st ng. Ma st Coulomb l bng , V lc ma st trn b mt mi tc ng theo hng ngc li chuyn ng ca n lin quan n b mt khc. l Arthur, Jules Morin , ngi gii thiu hn v chng minh tin ch ca h s ma st. [9] Cc h s ma st l mt thc nghim o lng - n c th o c bng thc nghim, v khng th tm thy thng qua tnh ton. B mt nhm hn c xu hng c gi tr hiu qu cao hn. C hai h s ma st tnh v ng lc ca cc ph thuc vo cp b mt tip xc, i vi mt cp ca cc b mt, h s ma st tnh thng ln hn ma st ng, trong mt s thit lp hai h s bng nhau, chng hn nh teflon trn teflon. Hu ht cc vt liu kh kt hp c gi tr h s ma st t 0,3 v 0,6. Gi tr bn ngoi phm vi ny l him , nhng teflon, v d, c th c mt h s thp l 0,04. Mt gi tr bng khng c ngha l khng c ma st tt c, mt ti sn kh nm bt - ngay c bay ln t xe ko . Cao su tip xc vi cc b mt khc c th mang li h s ma st 1-2. i khi n c duy tr lun lun
