Hgc sinh
- On tap lai cac kién thiie da hpc vl dao đng dilu hoạ
Ill - THlfiT Kfí HOAT D 6 N G DAY - HOC
Hoat đng cua hgc sinh
Hoat dgng 1
Kiem tra, chuan bj dieu kien xuat phat xuat phat
Trg giiip cua giao vi§n
GV neu cau hdi kilm tra kién thiic cu: - Viet phuong trinh đng luc hpc cua - Viet phuong trinh đng luc hpc cua
Hoat d d n g cua hgc s i n h Trg giiip ciia giao vien HS suy nghT ca nhan tim eau tra
idị
I Hoat dgng 2
i Lam bai tap 1 de ren luyen each I chiing minh mdt vat dao đng la ! dao đng dieu hoa
HS lam viec ea nhan, sau đ thao luan chung toan Idp.
VTCB
- Gpi m la khdi lupng ciia phii ke,
s la tiei dien phan ong cua phu kẹ Danh dau tren d'ng ciia phii ke vach
a ngang mire mat thoang ciia
chai long.
- Chpn true toa dp nhu hlnh ve, gdc toa dp tai vi tri giao dilm ciia mat thoang vdi true ciia phii kẹ Xet vat tai vi tri can bing :
-P + F^ = 0 (1)
Xet vat tai vi tri li dp z :
- P + F^- AF,, = ma
- Viei cae cdng thirc xac dinh chu kị
van tdc gdc. van tdc, gia tdc, dong nang, the nang, ca nang ciia con lie id xọ
GV yeu eau HS lam viec vdi phiéu hpc tap va giai bai tap 1.
GV neu cac cau hdi gpi y:
- Mud'n chiing minh phii ke dao đng dilu hoa thi ta phai chufng minh nhu the nao ?
- Can cii vao dau dl ta khing dinh mot vat dao đng la dao đng dilu hoa ? - Mud'n xay dung phuang trinh đng luc hpc ciia phu ke cin phai phan tfch cac lire tac dung vao phii ke khi phii ke d vi trf can bing.
- Can phai danh dau mot vach tren phii ke dl xac dinh vi tri can bing ciia phu ke, nen danh dau tai vi tri nao ?
- Chpn true toa dp, gdc toa dp.
- Xet vat (phu ke) d vi tri li dp z thi luc F^ tang hay giam mdt lupng bing bao
nhieủ
- Vilt phuang trinh dinh luat II Niu-ton cho vat d vi tri can bing va d vi tri li dp ;.
Hoat đng cua hgc sinh Trg giiip cua giao vien
o - P + F^ - pgsz = ma (2)
Thay (1) vao (2) ta dupc :
- pgsz = ma => -pgsz = mz" , „ , P f f l , _ r' + 0 D a t CO- = m 2 PgS =>z"+côz=0. m
Vay, phii ke dao đng dilu hoa vdi
tan sd goc co = Pg^ m
Hoat dgng 3
Lam bai tap 2 de ren luyen each tinh toan vdi phuong trinh dao dong dieu hoa
HS lam viec ca nhan, sau đ thao luan chung toan Idp.
a) Theo dau bai ta cd :
. , . TT 5TT
=>/ = 5;r TT\ 1 = — s 1
\OTT 30
Vao thdi dilm / = — s thi pha dao
30 STT đng bang — , khi đ : 6 ^ , 57r - , ^ X = z, 5 cos — = -2,16cm. 6 b) Theo dau bai :
x = 2,5cosO = l,25
cos 0 = 0,5 ^ = ±- + 2kTT, TT
3
GV yeu ciu HS tiép tuc lam viec vdi philu hpc tap va giai bai tap 2.
GV neu cac cau hdi gpi y:
- Dai lupng nao trong phuang trinh dao đng da cho la pha dao đng ?
- Pha ciia dao đng nhan gia trj nao khi x = 1,25cm ?
Hoat đng cua hgc sinh trong đ k la sd nguyen O = \0TTl + - = ± — + 2kTT 2 3 ^ k + — J 5 lOl 2 3 TT
Neu phan biet chi tiei : O = + — la 3
liic dilm M di qua vi trf x = 1,25cm
TT
theo chieu am vacl) = la liic 3
dilm M di qua vi tri x = 1,25cm theo chilu duong. Ki hieu P la dilm cd toa dp x = 1,25cm. Ta cd : - Thdi dilm M di qua P theo chilu
5 k. ,
duong :/ = + —(•^)- ^ 60 5
- Thdi dilm M di qua P theo chilu
am :/ = + —(^)- 60 5 c) Trong mdt chu ki 27r 2TT T = - 0,2s CO ]OTT
khoang dudng di dupc bing bdn lan bien đ : s = 4.2,5 = 10cm.
Trg giup cua giao v i e n
- Bilu diln dao đng dilu hoa bing mdt
TT
vecto quaỵ Khi đ, 0 = +— la liic
dilm M di qua vi trf x = 1,25cm theo chilu nao ? O = la liic dilm M di
3
Hoat đng cua hgc sinh Trg giiip cua giao vien Tdc dp trung binh trong mdt chu ki Tdc dp trung binh trong mdt chu ki
dao đng la: _ s 10 _ s 10
V = —= — = 50cm/s = 0,5m/s. 7 0,2 7 0,2
van tdc trung binh trong mdt chu ki dao đng bing 0. ki dao đng bing 0.
Hoat dgng 4
Lam bai t$p 3 de ren luy^n c ^ h viét phucrng trinh dao đfig cifi viét phucrng trinh dao đfig cifi mot dao dgng dieu hoa
HS lam viec ca nhan, sau đ thao luan chung toan Idp. luan chung toan Idp.
a) Dang tdng quat cua prfiiroHg trinh dao đng la : trinh dao đng la :
x = A cosicot + (p)
vai CO- — =lOradls. m m
Chpn md'c thdi gian t = 0 vao Wc
gd biia vao vat nang d vi trf can bang va chilu duang ciia true X la bang va chilu duang ciia true X la chilu van tdc ban daụ Ta cd dilu kien ban diu: khi r = 0 thi x = 0 va
V = 0,2ml s. Suy ra : I ^cos(^) = 0 Suy ra : I ^cos(^) = 0 [-6;^sin^ = 0,2 TT ^(p = ±— va -10^sin^ = 0,2. Ta tháy A > 0 TT 2" .4 = —0,02m. 10
GV yeu cau HS tiép tuc lam viec vdi phiéu hpc tap va giai bai tap 3. phiéu hpc tap va giai bai tap 3.
GV neu cac cau hdi gpi y: