Bin dng ca tm ch nht cha bin v nm

Chng 8. Nguyn l cng oI. Cc khi nimMt A ca vt th kho st c chia ra lm 2 min:

- mt chu hay mt chu lin kt. Trn mt ny ngi ta cho trc chuyn v

- mt chu cc ngoi lc cho trc. Trn mt ny ngi ta cho trc ti trng

Chng 8. Nguyn l cng oI. Cc khi nimi lng cho trci lng cha bit

Gi l trng chuyn v tht

l trng chuyn v o Trng o l mt trng chuyn v bt k, khng lin quan n trng tht, nhng tun theo nhng iu kin lin kt ca vt kho st

Chng 8. Nguyn l cng oI. Cc khi nim

Nu lin tc v o hm c, ta c th tm trng bin dng tht v o di dng:

(8.1)Cc trng ng sut tht v ng sut o tha mn cc phng trnh cn bng:

(8.2)v iu kin bin b mt:

(8.3)

Chng 8. Nguyn l cng oI. Cc khi nim

(8.4)

Cng o ca lc th tch trn chuyn v o :

Cng o ca lc o trn chuyn v :

(8.5)

Chng 6. Bi ton phng trong ta ccII. Nguyn l chuyn v hay nguyn l cng o

Kho st vt rn bin dng chu tc dng ca lc b mt v lc th tchCho n mt trng o cc chuyn v c lp vi chuyn v tht (chuyn v b)

Chng 6. Bi ton phng trong ta ccII. Nguyn l chuyn v hay nguyn l cng o

Cng ca ngoi lc v trn chuyn v o

- Cng ngoi lc o

(8.6)Gi s vt th cn bng. Thay Fi v Ti trong (8.2) v (8.3) vo (8.6):

S dng nh l Gauss, a tch phn b mt v tch phn th tch

Chng 6. Bi ton phng trong ta ccII. Nguyn l chuyn v hay nguyn l cng o

Do tnh i xng ca ij, tch phn ny c vit:

Gi WI l cng ni o:

T y ta c ng thc:(8.7)

Chng 6. Bi ton phng trong ta ccII. Nguyn l chuyn v hay nguyn l cng o

Nguyn l cng o:

Mt vt th bin dng cn bng, cng ngoi o bng vi cng ni o i vi tt c trng chuyn v o(chp nhn lin tc v o hm c)(8.8)

Chng 6. Bi ton phng trong ta cc* Ghi ch: 1. Nguyn l cng o din t s cn bng v cho ta nhng phng trnh cn bng 2. Nu trng o l tng thch th tch phn mt tr thnh

(8.9)Khi nguyn l cng o tr thnh:

(8.10)

Chng 6. Bi ton phng trong ta cc* Ghi ch:

4. Trn mt dx2dx3 ca phn t c bn, c tc ng ca lc php tuyn v c chuyn v tng ng l

Cc i lng ny sinh cng:

p dng tng t i vi cc thnh phn khc ta tm c biu thc

Chng 6. Bi ton phng trong ta ccIII. Nguyn l lc o hay nguyn l cng o bKho st vt th bin dng c:p dng cho n mt trng lc v ng sut o, c lp vi trng tht

Chng 6. Bi ton phng trong ta ccIII. Nguyn l lc o hay nguyn l cng o bTrong qu trnh thay i tht u, cc ngoi lc o v thc hin cng , gi l cng o b:

(8.11) trng o cn bng, ta a cc phng trnh (8.2) v (8.3) vo (8.11):

Bng cch tng t nh trn, ta c

Chng 6. Bi ton phng trong ta ccIII. Nguyn l lc o hay nguyn l cng o bVi gi thit trng chuyn v tht ui lin tc v o hm c, ta c th s dng biu thc (1.1), khi :

(8.12)Nguyn l cng o b:

(8.13) Nu nhng chuyn v v bin dng ca mt vt th bin dng c l tng thch, cc cng ngoi o b v cng ni o b bng nhau, i vi trng ng sut cn bng.

Chng 6. Bi ton phng trong ta cc* Ghi ch: 1. Nguyn l cng o din t s tng thch ng hc ca vt th v cho ta nhng iu kin tng thch. 2. Nu trng o l trng t ng sut cn bng ( ), th cng ngoi tr thnh:

(8.14)Khi nguyn l cng o b tr thnh:

(8.15)