## anhtam89(Dinh nghia va Dl momen dong luong

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```Cau 4
Dinh nghia va y nghia cua momen dong luong. trinh bay ca dinh ly va dinh luat ve momen dong luong
a) Dinh nghia:
xet 1 chat diem M chuen dong tren 1 quy dao (C) duoi tac dung cua luc F tai 1 thoi diem nao , chat diem o m xac dinh boi OM = r va no co dong luong K= m.v
khi do dai luong L= r..k goi la momen dong luong cua 1 chat diem doi voi o
vay : momen dong luong cua 1 chat diem la 1 dai luong vecto xd bang tich co' huong giua vecto ban kinh quy dao va vecto dongluong cua chat diem do'
voi chat diem chuyen dong tron : L= I.w
voi he chat diem : L=tong Ri.Ki
b) dinh ly ve momen
dK/dt=F
r..dk/dt=r..F
d(r..k)/dt=r..F
dL/dt=Mo(F)
vay: dao ham theo thoi gian cuamomen dong luong doi voi cua 1 chat dioemj chuyen dong bang tong momen doi voi O cua cac luc tac dung len chat diem voi chat diem
Voi chuyen dong tron
d(I.w)/dt= Mo(Ft)
Ft la luc tt
Tu' dL/dt = Mo(F)
dL=Mo(F)dt
tich phan dL tu l1 toi l2 = tich phan Mo(F)dt    tu1 t1 toi' t2
deltaL=tich phan Mo(F)dt
neu Mo(F) khong doi suy ra deltaL = Mo(F).deltat
vay:
do bien thien momen dong luong rtrong 1 khoang thoi gian bang xung luong cua momen luc tac dung len chat diem trong khoang thoi gian do'
c)
Dinh  luat momen dongluong
tu' dL/dt = M
suy ra neu M= 0 thi' dL/dt = 0 suyra L= const
Vay
Doi voi 1 he co chat diem co lap hoac chiu tac dung cua cac ngoia luc nhung tong momen cua cac ngoai luc ay' doi voi goc toa do bang o , thi tong mom dong luong cua he la 1 dai luong dc bao toan
Neu he chat diem chuyen dong xung quanh 1 truc co dinh
d(I1w1+I2w+....) = M=0
suy ra (....)= const
suy ra vay ran quay xunh quay 1 truc co dinh m=0
suy ra Iw= const```