Thiết kế bài giảng vật lý 12 nâng cao (tập 1) phần 1

TRAN THUY HANG HA DUY£N TUNG

NANG CAO
TAPMOT

NHA XUAT BAN HA NOI

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TRAN THUY H A N G

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- H A DUYfiN TUNG

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THIET KE BAI GIANG
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NANG CAO - TAP 1

NfiA XUAT BAN HA NOI

.ai not ddu
Thie't ke bai giang Vat li 12 nang cao dvroc viet theo chifdng
trinh sach giao khoa m6i ban hanh nam 2006 - 2007. Sach gidi
thif u m6t each thi§'t ke bai giang VSt li nang cao theo tinh than
doi mdi phifdng phap day - hoc, nham phat huy tinh tich ciTc
nhan thiic cua hoc sinh.
Ve noi dung : Sach bam sat noi dung sach giao khoa VSt li 12
theo chifdng trinh nang cao. O moi tie't, sach chi ro muc ti§u ve
ki^'n thiic, ki nSng, c»c c6ng viec chuan bi ciia giao vi^n va hoc
sinh, cac phtTOng tien ho trd giang day can thie't, nham dam bao
chat Iifdng tufng.bai, timg tie't len Idp. Ngoai ra sach co md rong,
bo sung them m6t sd' ndi dung lien quan tdi bai hoc bang nhieu
hoat dong nham cung cS'p them tu" lieu d6 cac th^y, co giao tham
khao vSn dung tuy theo do'i ttfdng hoc sinh tiing dia phiTdng.
Ve phifdng phap day hoc : Sach diTdc tri^n khai theo hvrdng tich
cue hoa hoat ddng cua hoc sinh, lay cd sd cua moi hoat dong la
nhiing viec lam cua hoc sinh dudi su" htrdng d i n , phvi hdp vdi
dac trvmg mon hoc nhiT : thi nghif m, thao luan, thu'c hanh, nham
phat huy tinh doc lap, tu" giac cua hoc sinh. Dac bi^t, sach rat
chii trong khau thu'c hanh trong timg bai hoc, ddng thdi ciing chi
ro tung hoat ddng cu thg cua giao vien va hoc sinh trong mdt
tiS'n trinh day hoc, coi day la hai hoat ddng ciing nhau trong do
ca hoc sinh va giao vign la chu the.
Chiing tdi hi vong cud'n sach nay se la mdt cdng cu thie't thUc,
gop p h i n hd trd cac thiy, cd giao giang day mdn Vat li 12 trong
viec nang cao hif u qua bai giang cua minh.
Cac tac gia


CHi/ONG 1. DONG Ll/C HOC VAT RAN

•

•

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•

BAII

CHUYEN D 6 N G

QUAY

CUA VAT

RAN

QUANH M 6 T TRUC c 6 DESfH
I - MUC TifiU
1. V^" kien thtic
- Hoc sinh hieu duoc khai niem vat rdn va chuyen ddng tinh tien cua vat ran la gi.
- Hoc sinh hieu duoc khai niem toa dp goc (p.
- Xay dung dupe cac cdng thiic tdc do goc co, gia tdc gdc y.
- Nam viJng cac cdng thiic lien he giiJa tdc do gdc va tdc do dai, gia tdc gdc va gia
tdc dai ciia mot diem tren vat rSn.
- Xay dung dupe cac phuong trinh ddng hpc ciia chuyen ddng quay.
- Van dung dupe eac cdng thiic ciia chuyen ddng quay deu, quay bie'n d6i diu de
giai cac bai tap don gian.
2. Ve ki nang

- Ren luyen cho hpc sinh kT nang sii dung phuang phap tuong tu de xay dung cac
khai niem, cdng thiic cua chuyen ddng cua vat ran.
II - CHUAN BI
Giao vien
- Ve hlnh 1.1, 1.2, 1.4, 1.6 trdn gia'y kho AQ.
Hoc sinh
- On tap lai phin ddng luc hoc chat diem b Vat li Idp 10 THPT.


Ill - THifiT Kfi' HOAT D 6 N G DAY - HOC
Hoat d o n g cua hoc sinh

Tror giiip cua giao vien

Hoat dong 1
Kiem tra, chuan bi dieu' kien
xuat phat. Dat van de

GV neu cau hdi kiem tra kie'n thiie cu.
- Neu khai niem vat ran.
- Chuyen ddng tinh tien la gi ?

HS suy nghT ca nhan tim cau tra
Idi.

HS nhan thiic dupe van de cua bai
hpc.

- Viet phuong trinh chuyen ddng cua
vat chuyen ddng thing bie'n doi deu.

Viet cdng thiic van tdc cua vat dd.
Dgt vdn de : 6 Idp 10, chiing ta da xac
dinh quy luat chuyfin ddng ciia vat ran
chuyen ddng thang bie'n doi deu. Bai
hpc nay chiing ta di sau tim hieu va xac
dinh quy luat chuyen ddng, tim mdi lien
he giOa eac dai lupng dac trung cho
chuyen ddng quay cua vat ran quanh
true CO dinh.

Hoat dong 2
Tim hieu khai niem toa do goc
HS quan sat hinh ve 1.1 tren kho
gia'y AQ, suy nghT ca nhan tim eau
tra Idi.
— Mdi diem tren vat vach mdt
dudng tron nam trong mat phang
vudng gdc vdi true quay,
n
kinh bang khoang each tir di6m do
de'n true quay, tam ciia quy dao
nam tren true quay.
- Mpi diem ciia vat deu quay duoc
cung mdt gdc trong cung mdt
khoang thdi gian.

GV neu cau hoi de HS tim hieu khai
niem toa dp gdc:
- Xet.mdt vat ran bat ki quay quanh mdi
tmc Az t d dinh (Hinh 1.1 SGK). Hay

cho bie't dac diem ciia quy dao cua mdt
di6m tren vat ran khi vat ran chuyen ddng
va gdc quay ciia cac diem tren vat ran?


Tro g i u p ciia giao vien

Hoat d o n g cua hoc sinh

: GV thdng bao:

HS tie'p thu, ghi nhd.

; - Quan sat tren hinh ve, vi tri cua vat tai
mdi thdi diem se dupe xac dinh bang
mdt gdc (p giira mat phang ddng P gin
vdi vat va mdt mat phing cd dinh PQ.
Gdc

Dan vi cua toa dp gdc p la radian (rad).
- De don gian, ta chi xet miic dp quay
theo mdt chi6u va chpn chifiu duong la
chieu quay ciia vat, khi dd g)>0.
Hoat dong 3
Xay dung khai niem toe do goc
trung binh va tdc do goc tiic thdi

GV neu cau hdi de HS xay dung khai
niem tdc dp gdc:

HS thao luan chung toan Idp.

j

- Khi vat rin quay, su bie'n thien theo
thdi gian ciia (p the hien quy luat
chuyen ddng quay cua vat rin. Hay tim
mdt dai lupng dac trung cho miic dp
quay nhanh hay cham eiia vat rin. Dai
lupng dd dupe xac dinh nhu the nao ?
GV neu cae cau hdi gpi y:

- Dai lupng dac trung cho miic dp |
quay nhanh hay cham dupe xac :

- Trong chuyen ddng thing, dai lupng
nao dac trung cho chuyen ddng nhanh
hay cham ciia vat ? Dai lupng dd dupe
xac dinh nhu the nao?

dinh bang thuong so —^ •
At

'
:

- Tuong tu, trong chuyen ddng quay, ta
cd the tim mdt dai lupng dac trung cho
miic dd quay nhanh hay cham ciia vat
rin dupe khdng ?
- 0 thdi diem t, toa dp gdc ciia vat la g).

0 thdi diem t +At, toa dp gdc ciia vat la


Hoat dong ciia hoc sinh

Tror giup cua giao vien
(p + A(p, dai lupng dac trung cho miic
dp quay nhanh hay cham ciia vat rin
dupe xac dinh nhu the nao ?
GV thdng bao:
- Dd chinh la tdc dp gdc trung binh j
C0f^J =

cua vat rin trong khoang thdi

At
gian At.
HS thao luan chung toan Idp.
- Tdc dp gdc tiirc thdi d mdt thdi
diem t duoc xac dinh bing gidi han

- GV yeu cau HS xay dung cdng thiic
xac dinh tdc dp gdc tiic thdi va cho biet
don vi cua tdc dp gdc.

ciia ti sd —^ khi A / tien dan tdi 0.
At
co = hm

i^

hay ft) = ^ (t)

A/->0 At

- Don vi ciia tdc dp gdc la rad/s.
Hoat dong 4
Xay dung khai niem gia tdc goc
trung binh va gia tdc goc tiic thoi

GV neu cau hdi de HS xay dung khai
niem gia tdc gdc:
- Hay tim mdt dai lupng dac trung cho
su bie'n thien nhanh hay cham ciia tdc
dp gdc. Dai lupng dd dupe xac dinh nhu
the nao?

HS thao luan chung toan Idp.
- Dai lupng dac trung cho su bie'n
thien nhanh hay cham cua tdc dp
gdc dupe xac dinh bing thuang so
Aco
At

GV neu cac cau hdi gpi y
- Trong chuyen ddng thing, dai lupng
nao dac trung cho sir bie'n thien nhanh
hay cham ciia van tdc ? Dai lupng dd
dupe xac dinh nhu the nao ?
- Tuang tu, trong chuyen ddng quay, ta
ed the tim mdt dai lupng dac trung cho

Trd giiip cua giao vien

Hoat dong cua hoc sinh

su bie'n thien nhanh hay cham ciia tdc
dp gdc dupe khdng ?
- O thdi diem t, vat cd tdc dp gdc la co.
O thdi diem t + At, vat cd tdc dd gdc la
(o + Ao).

dai lupng dac trung cho sir

bie'n thien nhanh hay cham cua tdc dd
gdc dupe xac dinh nhu the nao?
GV thdng bao:
- Dd chinh la gia tdc gdc trung binh
Ao)
Yi^ =

HS thao luan chung toan Idp
- Gia tdc gdc tire thdi d mdt thdi
diem t dupe xac dinh bing gidi han
,

,

. Aft) , , . »

cua tl so

..-J.-

, , ,, ,
...
cua vat ran trong khoang thai

At
gian At.
- GV yeu cau HS xay dung cdng thiic
xac dinh gia tdc gdc tiic thdi va cho bie't
don vi cua gia tdc gdc.

,. r,

khi A r tien dan tOi 0.
At

7 = Hm

hay y = coit)

,v->o At
-)

- Dan vi cua gia tdc gdc la rad/s .
Gia tdc gdc tiic thdi ciia vat rin
quay quanh mdt true d thdi diem t
la dai lupng dac trung cho su bie'n

thien ciia tdc dp gdc d thdi diem
dd va dupe xac dinh bang gdi han
, , ^, Ao) ., . . .., ,.- ,. _
cua tl so
khi A t tien dan toi 0.
At
Hoat ddng 5
Xay dung cac phuong trinh dong
hoc ciia chuyen ddng quay

GV yeu cau HS phat bilu khai niem gia
tdc gdc.

GV neu cau hdi de HS xay dung phuang
trinh chuyen ddng ciia vat rin quay deu:


Hoat dong cua h9c sinh

Trg giup cua giao vi^n
- Trong trudng hpp tdc dd gdc ciia vat
rin khdng doi theo thdi gian thi chuyen
ddng ciia vat rin la chuyen ddng quay
d6u. Toa dp gdc ciia vat d thdi diem /
dupe xac dinh nhu the nao ?

HS thao luan chung toan Idp.

GV neu cac cau hdi gpi y.
- Hay neu su tuang ling giOa cac dai

lupng gdc trong chuyen ddng quay va
cae dai lupng dai trong chuyen ddng
thing?

- Viet phuong trinh chuyen ddng ciia
vat chuyen ddng thing deu. Tuong tu
rin quay diu la : (p = (pQ + cot, trong
nhu vay chiing ta cd the vie't dupe
dd q)Q la toa dp ban dau luc f = 0.
phuang trinh chuydn ddng cho vat
chuyfin ddng quay diu nhu the nao ?

Phuong trinh chuyen ddng ciia vat

GV neu cau hdi de HS xay dung cac
cdng thiic trong chuyen ddng quay bie'n
doi deu:
- Trong trudng hpp gia tdc gdc ciia vat
rin khdng doi theo thdi gian thi chuyen
ddng ciia vat rin la chuyen ddng quay
bie'n doi deu. Hay vie't cdng thiic xac
dinh tdc dp gdc ciia vat d thdi diem t,
phuang trinh chuyen ddng eiia vat rin,
cdng thiic ddc lap vdi thdi gian trong
chuyen ddng quay.
HS thao luan chung toan Idp.
- Cdng thiic xac dinh tdc dp gdc
ciia vat chuyen ddng trdn bie'n doi
deu tai thdi diem / la :
co = coQ + yt

10

GV neu cac cau hdi gpi y:
- Viet cdng thiic xac dinh van tdc ciia
vat chuyen ddng thing bie'n doi deu tai
thdi diem t, phuong trinh chuyen ddng
eiia vat va cdng thiic lien he giira van
tdc, gia tdc va dp ddi.


Hoat dong cua hoc-sinh

Trd giup cua giao vien

- Phuang trinh chuyen ddng quay
bie'n ddi diu :

- Tuong tu cac cdng thurc cua chuyen
ddng thing bie'n ddi deu, hay vie't cac
cdng thiic cua chuyen ddng quay.

1 2

- Cdng thiic ddc lap vdi thdi gian
0}^-Q)Q=2r{(p-q)Q)

Trong dd, ^Q' ^o 1^ ^^^ '^O goc va tdc
dp gdc ban dau tai thdi diem t = 0.
GV thdng bao:

HS tie'p thu, ghi nhd.

- Ne'u vat quay theo mdt chilu nhat
dinh va tdc dp gdc o) tang theo thdi
gian thi chuyen ddng quay la nhanh dan

ir>0).
- Neu tdc dp gdc giam dan theo thdi
gian thi chuyen ddng quay la cham din

ir<0).
Hoat dong 6
Tim hieu cac dac diem cua van
toe va gia toe ciia cac diem tren
vat quay

GV neu cau hdi de HS tim hiiu cac dac
diem ciia van tdc va gia tdc cua cac
diem tren vat quay.
- Ne'u vat rin quay khdng deu thi gia
tdc cua mdt diem tren vat rin dupe xac
dinh nhu the nao ?

HS thao luan chung toan Idp.

GV neu cac cau hdi gpi y:

- Ne'u vat rin quay d6u thi gia tdc
cua mdt diem tren vat rin dupe xac

dinh:

- Ne'u vat rin quay deu, gia tdc ciia mdt
diem tren vat rin dupe xac dinh nhu the
nao ? Cd the su dung cdng thiic gia tdc
hudng tam da hpc d Idp 10 de xac dinh gia
tdc eiia mdt diem tren vat rin dupe
khdng ?

v'

2

.

.

,

a„- — = 0} r, gia toe a^ dac trung
r
cho su thay doi ve hudng eia van
tdc dai V.

11


Hoat dong ciia hoc sinh

Trg giup cua giao vien

1

:
:

- Neu vat rin quay khdng deu thi ;
mdi diem ciia vat rin cung chuyen \
ddng trdn khdng deu. Khi dd vecto :
van tdc v ciia mdi diem thay doi :
ea ve hudng lin dp Idn. Khi dd, ;
vecto gia tdc ciia mdi dilm cd hai
thanh phan :
Thanh phan Z^ cd phuong vudng •

- Khi dd, gia tdc cua mdt dilm tren vat 1
rin dac trung cho tinh chat gi ciia van ,
tdc dai V ciia nd ?
- Neu vat rin quay khdng deu thi vecto j
van tdc dai v cd dac diem gi ?
i
- Cd thi sii dung hai thanh phin gia tdc
dl dac trung cho sir thay ddi ve hudng
va ve dp Idn cua vecto van tdc dai v
dupe khdng ? Ne'u dupe, thi hai thanh
phan cua vecto gia tdc dupe xac dinh
nhu the nao ?

gdc vdi V, dac trung cho sir thay ;
doi ve hudng ciia v, thanh phan •
nay chi'nh la gia tdc hudng tam.

;

Thanh phan a, cd phuang ciia v, \
dac trung cho sir thay doi ve dp Idn •
ciia V
Av

V - VA

;

a, = — =
At
At
Aco
rco - rcOf)
=
- =r
= ry
Al
At

:
I
•
;

- Dp Idn cua vecto gia tdc toan ; - Vecto gia tdc toan phin duoc xac dinh
phan dupe xac dinh

; ; thdng qua hai thanh phan vecto gia tdc
; hudng tam va tiep tuye'n nhu the nao ?
/ 2
2
a = ^a„+a,
:
- Hudng ciia vecto gia tdc toan |
phan duac xac dinh vecto a hpp ;
vdi ban kinh OM gdc a, vdi i
tana = - ^ = ^ -

a,

Y

•

««

CO

;

12

;


i

Trg g i u p ciia giao vien

Hoat d o n g cua hoc sinh

1

1 Hoat dong 7
Cling cd bai hpc va djnh hudng
nhiem vu hoc tap tiep theo

GV yeu cau HS lam viec vdi phieu hpc
; tap; - Yeu cau HS dn tap lai eac kie'n thii'c
; vl: mdmen lire, phuong trinh ddng lire
; hpc ciia chat dilm, y nghTa cua khdi
;lupng.

PHIEU HOC TAP
Cau 1. Mdt canh quat dai 20cm, quay vdi tdc dp gdc khdng doi la 94 rad/s. Tdc dp
dai cua mdt dilm d vanh canh quat bing
A. 37,6 m/s.

B. 23,5m/s.

C.l8,Sm/s.

D. 47m/s.

Cau 2. Banh da cua mdt ddng co tir liic khdi ddng de'n liic dat tdc dp gdc 140rad/s
phai mat 2s. Bie't ddng ca quay nhanh dan diu. Gdc quay ciia banh da
trong thdi gian tren bing

A. 140 rad.

B. 70 rad.

C. 35 rad.

D. 35 n rad.

Cau 3. Mdt banh xe quay nhanh din diu quanh mdt true. Liic t = 0 banh xe cd tdc
dp gdc 5 rad/s. Sau 5s tdc dp gdc cua nd tang len de'n 7 rad/s. Gia tdc gdc
cua banh xe la
A. 0,2rad/s'

B. 0,4rad/sl

C. 2,4rad/s^

D. 0,8rad/s^

Cau 4. Hai dilm M,, M2 tren mdt dTa CD, khoang
each tir tam cua dTa den hai dilm lan lupt la
2
/?,, 7?2 v^ R\=-R2Cho dTa CD quay deu
quanh mdt true vudng gdc vdi tam ciia dTa.
a) Ke't luan nao sau day diing khi ndi vl gdc quay
ciia hai dilm trong cung mot khoang thdi gian ?

13

A . (Pi =^
B. ^2=-^!-

C. (P2=(P\.

D. (P2 -(i(P\.

b) Ke't luan nao sau day diing khi ndi vl tdc dp gdc ciia hai dilm ?
2
A. &>i = —(y2-

2
B. &>2 = —
C. <i>2=9ft)|.

D. 0)2=0}^.

c) Kit luan nao sau day diing khi ndi vl tdc dp dai cua hai dilm ?
2
A. V, =-V2.

2
B. V 2 - - V , .

C. V2=2v|.

D. V2=3v].

BAI2

PHUONG TRINH D O N G L U C HOC CUA VAT R A N
QUAY QUANH M 6 T TRUC c6 DEsJH
I - MUC TifiU
1. Ve kie'n thiic
- Xay dung dupe bilu thiic bilu diln md'i lien he giira gia tdc gdc va mdmen lire
ciia vat rin cd true quay cd dinh.
- Dua ra eac du doan vl su phu thudc eiia mdmen quan tinh va thiet ke dupe
phuang an thi nghiem kilm tra du doan.
- Nim dupe khai niem mdmen quan tinh dd'i vdi mdt true cua vat rin.
- Nim va van dung dupe phuang trinh ddng luc hpc cua vat rin quay quanh mdt
true dl giai dupe mdt sd bai tap.
2. Ve ki n a n g
- Van dung kie'n thiic vl mdmen luc da hpc d Idp 10 dl xay dung bilu thiic bilu
diln mdi lien he giira mdmen luc tac dung vao vat rin va gia tdc gdc.

14


- Ren luyen kT nang dua ra cac du doan cd can cii.
- Ren luyen kT nang thiet ke cac phuang an thi nghiem kilm tra du doan, thu thap
sd lieu, xu li sd lieu va dua ra ket luan.
- Van dung phuang trinh ddng luc hpc ciia vat rin quay quanh mdt true de giai
mdt sd bai tap.
II - CHUAN BI
Giao vien
- Bd thi nghiem khao sat chuyin ddng tinh tien - chuyin ddng quay ciia he vat.
- Ve bang 2.1 vao giay kho AQ.
Hgc sinh

- On tap lai kie'n thiie vl mdmen luc, phuang trinh ddng luc hpc ciia chat dilm, y
nghTa ciia khd'i lupng.
III - THlfiT Kfi' HOAT DONG DAY - HOC
Hoat dgng cua hgc sinh

Trg giiip cua giao vien

Hoat dong 1
Kiem tra, chuan bi dieu kien
xuait phat. Dat van de
HS suy nghT ca nhan tim cau tra Idi.
- Tir bilu thire tinh mdmen cua lire :
M - F.d, suy ra tac dung lam quay
canh cira ti le vdi tich dp Idn ciia
luc tac dung va canh tay ddn cua nd.
- Bilu thiic ciia dinh luat II Niuton
_ F
a- —
m
HS nhan thiic dupe van dl cua bai
hpc.

GV neu cau hdi kilm tra kien thiic cu:
- Tac dung lam quay canh ciia phu
thudc vao yeu td nao ? Bilu thiic toan
hpc nao bilu thi dilu dd ?

- Viet bilu thiic ciia dinh luat II Niu-ton.
Dgt vdn de : Trong chuyin ddng ciia
cha't dilm, giiia gia tdc cua chit dilm va

lire tie dung cd mdi lien he dupe diln ta
bing dinh luat II Niu-ton. Trong chuyin
ddng quay cua vat rin, gia tdc gdc va
mdmen luc cd mdi lien he vdi nhau nhu
the nao ?

15


Hoat d g n g cua hgc sinh

Trg giiip cua giao vien

Hoat ddng 2
Tim mdi lien he giua gia tdc gdc
va mdmen luc
HS suy nghT ca nhan, sau dd thao
luan chung toan Idp.

GV yeu cau HS tim bilu thiic toan hpc
bilu diln mdi lien he giiia mdmen lire
va gia tdc gdc trong chuyin ddng quay
eiia vat rin.
GV neu cac cau hdi gpi y:

O- ^

- Xet trudng hop don gian nha't la vat
rin gdm mdt qua cau nhd khd'i lupng m
gin vao mdt dau thanh rat nhe, dai /•.

Vat chi chuyin ddng quay tren mat
phing nhin nim ngang xung quanh mdt
true thing diing di qua dau O ciia thanh.
Khi dd bilu thiic lien he giira mdmen
lire va gia tdc gdc dupe viet nhu the nao ?

T,

- Luc tac dung theo phuang nao thi gay
gia tdc tie'p tuye'n a, cho vat ?
Luc F, gay ra gia tdc tie'p tuyen

- Mdmen ciia luc F, dd'i vdi true quay

cho vat: F, = ma,.

O dupc xac dinh nhu the nao ?

Mdmen ciia luc F, dd'i vdi true
quay O : M - F,r = majr
=i> M = I wr jY

- Mdmen tac dung len mdi chat
dilm dupe xac dinh M, = I m^r, 1 Y
- Vl cac cha't dilm ciia vat rin cd
cung mdt gia tdc gdc nen mdmen
tac dung len vat rin dupc xac dinh :
(

\

I /

/

M = Y,M,=
I

16

- Gia tdc tie'p tuye'n a, cd lien he vdi
gia tdc gdc Y r^hu the nao ? Bilu thiic
bilu diln mdi lien he giiia gia tdc gdc
ciia vat rin va mdmen luc dupc vilt nhu
the nao ?
- Ne'u vat rin gom nhilu chat dilm khdi
lucmg Wp m,.. a each true quay nhirng
khoang each i\, /j,... khac nhau thi
mdmen tac dung len mdi chat diem
dupc vilt nhu the nao ? Mdmen tic
dung len vat rin dupc xac dinh nhu the
nao ?


Trg giiip cua giao vien

Hoat d g n g cua hgc sinh
Hoat dong 3
Xay dung khai niem mdmen [
quan tinh, vie't phuong trinh ;

ddng luc hgc ciia vat ran quay ;
quanh mot true cd djnh

GV neu cau hdi vl van de cin nghien
ciiu:

- Dai lupng ^ w ^ r , trong bilu thiic
/

lien he giira mdmen ciia vat rin vdi
gia tdc gdc dac trung cho tinh chat gi
ciia vat rin ? Dai lupng dd phu thudc
vao nhiing yeu td nao ?
HS thao luan chung toan lap va j
•
dua ra du doan.
- Dai lupng ^ ^ , 7 - , dac trung ;
/

'•

cho miic quan tinh cua vat quay. |

GV neu cac cau hdi gpi y:
- T i r b i l u thiic lien he giira mdmen ciia
vat rin vdi gia tdc gdc, vdi ciing
mdmen tie dung, vat rin nao cd dai
lupng Z ' " , ' ' , Idn thi gia tdc gdc cd

HS dua ra cac du doan :

Du dodn I : Dai lupng ^ m,r, phu |

gia tri nhu the nao ?,Cd d l dang thay
doi van tdc gdc cua vat rin hay khdng ?

thudc vao mdmen luc tie dung ;
len vat rin va gia tdc gdc ma nd i
\^
2 M
g a y r a : 2^m,r, =

I

r

Dudodn 2 : Dai lupng ^'W/A', chi ;
/

1

phu thudc vao khd'i lupng ciia vat •
rin va su phan bd khdi lupng ciia •
vat rin.
i
HS thao luan chung toan Idp dl •
thiet ke phuang an thi nghiem.

GV yeu cau HS thie't ke phuong an thi
nghiem dl kilm tra cac du doan tren.

- Can phai cd mdt vat rin, tac ;
dung vao vat rin va do mdmen luc ;
•
dd, do gia tdc gdc ciia vat rin.

GV gidi thieu bd thi nghiem va gpi y.

17


Hoat d g n g cua hgc sinh

Trg giiip cua giao vi§n

- Tac dung luc vao vat ran bing
cac qua gia trpng, luc tac dung vao
vat rin bing luc cang T.

- Mdmen luc tac dung vao vat rin:
M = T.R. Can phai xac dinh dp Idn
luc T va ban kinh R.
Luc T = m^ig - (3|), vdi m,, a, la
khdi lupng va gia tdc ciia qua gia
trpng.

- Gia tdc ciia qua gia trpng dupe
2sx
xac dinh: a^ ="V' Vay mdmen
tx

luc tac dung vao dTa trdn cd thi
xac dinh :

- Chiing ta cd bd thi nghiem: gom cac
vat rin la nhiing dTa trdn (1, 2, 3) cd the
quay quanh true di qua tam dTa. Cac dia
trdn gidng nhu cac rdng rpc. Tac dung
lire vao vat rin bing each nao ?
- Xac dinh mdmen luc tac dung vao vat
rin nhu the nao ?
- Tren bd thi nghiem cd bd tri 2 cong
quang dien va ddng hd do thdi gian, cd
the xac dinh dupe gia tdc ciia qua gia
trpng dupc khdng ?

M=T.R=m\(g-a\)R
=m,(8-^-)R
- Gia tdc gdc cua vat dupc xdc
dinh thdng qua gia tdc tie'p
tuye'n, mat khac gia tdc tie'p

- Gia tdc gdc ciia vat rin dupe xac dinh
nhu the nao ?
- Gia tdc gdc ed quan he vdi gia tdc tie'p
tuye'n nhu the nao ?


Hoat dgng cua hoc sinh

Trg giiip ciia giao vien

tuye'n chinh bing gia tdc cua gia
—•
trong. Vl vay Y = —^ =
R
R,t,'
- Tien hanh thi nghiem vdi luc
tac dung la T,, xac dinh dai

- Can phai tien hanh thi nghiem nhu the
nao dl kilm tra du doan 1.

lupng y^mjrj tuong irng. Sau dd
tiln hanh thi nghiem vdi luc tac
dung 7^2, xac dinh dai lupng
^W,A; tuang ling. Tir dd riit ra
ke't luan.
HS chii y quan sat, ghi sd lieu, xir
li sd lieu va riit ra ke't luan.

GV tien hanh thi nghiem dl kilm tra du
doan thii nha't ciia HS.

Ke't ludn : Vdi mdt vat rin cd true
quay nhit dinh, thay doi mdmen
luc tac dung vao vat rin thi gia tdc
gdc thay doi nhung ^/W/A", ludn
la mdt hing sd. Vay dir doan 1 la
khdng chinh xac.
GV neu cau hdi vl thi nghiem can phai

tiln hanh dl kiem tra du doan 2.
- Can phai tien hanh thi nghiem
vdi hai dTa trdn cd cung chat cau
tao, cung khd'i luang nhung ban
kinh khac nhau (su phan bd khdi
lupng khac nhau). Xac dinh dai

- De kilm tra du doan 2 can phai tien

lupng Z»i,r,^ (viec xac dinh dai

/?3 = 5cm.

hanh thi nghiem nhu the nao ? Biet ring
eac dTa trdn cd khd'i lupng va ban kinh
lan lupt nhu sau : W] = 800g, R^ = 5cm;
W2 = 800g, R2 = 2,5cm;

m^ = 400g,

19


Hoat dgng cua hgc sinh
lupng

^m^ri

Trg giiip cua giao vien

gidng nhu thi

nghiem vira tien hanh d ben
tren). Tir dd riit, HS ra ket luan.
- Can phai tien hanh thi nghiem
vdi hai dTa trdn cd cung ban kinh
nhung khdi lupng khac nhau. Xac
dinh dai lupng ^ w / , . . Tit dd,
HS riit ra kit luan.
HS chii y quan sat, ghi sd lieu, xir
li sd lieu va riit ra kei luan.

GV tien hanh thi nghiem.

Kei ludn : Dai lupng ^ OT,r, khdng
chi phu thudc vao khdi lupng eiia
vat rin ma cdn phu thudc vao sir
phan bd khdi lupng cua vat rin.
HS tiep thu, ghi nhd.

GV thdng bao:
- Mdmen quan tinh / ddi vdi mdt true la
dai luong dac trung cho miic quan tinh
cua vat rin trong chuyin ddng quay
quanh true ay.
i

- Dp Idn ciia mdmen quan tinh cua vat
rin khdng chi phu thudc vao khd'i
lupng ciia vat rin ma cdn phu thudc

vao su phan bd khd'i lupng ciia vat rin.
- vay ta cd thi vie't: M - l.y, phuang
trinh nay gpi la phuang trinh ddng luc
hpc ciia vat rin quay quanh mdt true.

20


Trg giiip cua giao vien

Hoat dgng ciia hgc sinh

Day la phuang trinh co ban ciia chuyin
ddng quay ciia vat rin.
Hoat dong 4
Van dung phuong trinh co ban ;
ciia chuyen ddng quay ciia vat :
rin de lam bai tap

GV yeu ciu HS lam viec vdi phieu hpc ••
tap dl lam bai tap.
1

HS suy nghT ca nhan, sau dd thao ;
luan nhdm va dai dien nhdm len ;
bao cao kit qua.
;
Ap dung dinh luat II Niu-ton cho ;
chuyin ddng tinh tiln cua thiing ;
nude, ta cd :

;
mg-T

= ma

(1)

Ap dung phuang trinh ddng luc •
hpc cho chuyin ddng quay cua vat ;
hinh tru, ta cd :
;
M = TR= l.Y

(2)

:

GV neu cac cau hdi gpi y:
- Viet phuang trinh dinh luat 11 cho
thiing nude.
- Viet phuang trinh ddng lire hpc cho
vat rin la hlnh tru cd true quay.
- Mdmen quan tinh dupc xac dinh nhu
the nao ?
- Gia tdc gdc dupc xac dinh thdng qua
gia tdc tie'p tuye'n nhu the nao ?

Mat khac, ta lai cd : y = —, thay •
R

•

. (2)
,ox va- rut
'. ra : Trr = -^
ly = -—•
la • '• :
vao
:
R R^
j
Thay T vao (1) ta dupc :
ma

la

- ma

;

R^
mg
m+

1
1

-^

R-

,

1

\+

^

r-

mR^

1
\
•

;

Hoat dong 5
Cling cd bai hgc va dinh hudng :
nhiem vu hoc tap tie'p theo

- GV yeu eau HS lam viec vdi bang 2.1
SGK dl tim sir tuong tu giira hai phuang

21


Hoat d g n g ciia hgc sinh

HS lam viec chung toan Idp.

Trg giiip cua giao vien
trinh ddng luc hpc cua chuyin ddng
quay va chuyin ddng tinh tien.
- GV yeu eau HS lam bai tap cdn lai
trong phieu hpc tap.
- HS vl nha lam cac bai tap cdn lai
trong SGK.
- HS vl nha dn lai cac kie'n thiic vl
ddng lupng va dinh luat bao toan ddng
lupng d vat li Idp 10 THPT.

PHIEU HOC TAP
Cau 1. Mdt thimg nude dupe tha xudng gilng nhd
mdt spi day dai quan quanh mdt hinh tru cd
ban kinh R va mdmen quan tinh /. Khd'i
lupng cua day khdng dang ke. Hinh tru coi
nhu quay tu do khdng ma sat quanh mdt true
cd dinh. Khd'i lupng cua thiing nude la m.
Tinh gia tdc cua thiing nude.
Cau 2. Mdt mdmen lire khdng ddi tac dung vao mdt vat co iiuv quay cd dinh.
Trong nhirng dai lupng dudi day, dai lupng nao khdng phai la hing so ?
A. Mdmen quan tinh.
B. Gia tdc gdc.
C. Khd'i lupng.

D. Tdc dp gdc.

Cau 3. Hai chat dilm cd khd'i lupng 1 Z:^ va 2 kg duac gin d hai dau cua mdt

thanh nhe cd chilu dai Im. Mdmen quan tinh cua he, dd'i vdi true quay di
qua trung dilm cua thanh va vudng gdc vdi thanh, cd gia tri

22

A. 1,5 kg.m

B. 0,75 kg.m^

C. 0,5 kg.m^

D. 1,75 kg.m^


Cau 4. Mdt vat hinh cau dac khd'i lupng m = 0,5kg,
ban kinh R = 0,2m. Mdmen quan tinh ciia nd
dd'i vdi true quay di qua tam la
A. 0,02 kg.m^
B. 0,04 kg.m^
C. 0,06 kg.m^
D. 0,08 kg.m^
Cau 5. Ke't luan nao sau day sai khi ndi vl mdmen quan tinh cua vat rin ?
Mdmen quan tinh cua vat rin phu thudc vao
A. khd'i lupng ciia vat.
B. gia tdc gdc cua vat.
C. hlnh dang va kich thudc cua vat.
D. vi tri cua true quay.

BAI3

M6MEN D6NG LUONG
DINH LUAT BAO TOAN M6MEN B6NG LLTONG
I-MUCTlfiU
1. Ve kien thtic
- Xay dung dupc dang khac ciia phuang trinh ddng luc hpc cua vat rin chuyin
ddng quay, tim dupe su tuong tu giita phuang trinh dd vdi dang khac cua phuang
trinh dinh luat II Niu-ton.
- Hiiu dupe khai niem mdmen ddng lupng.
- Nim dupc dinh luat bao toan mdmen ddng lupng, dilu kien dl mdmen ddng
lucftig cua vat rin chuyin ddng quay dupe bao toan.
- Hiiu dupc thi nghiem kilm nghiem mdt each dinh tinh dinh luat bao toan
mdmen ddng lupng.

23


2. Ve ki n a n g
- Ren luyen kT nang Idgic toan hoc dl tim phuang trinh ddng luc hpc ciia vat rin
chuyen ddng quay dang khac.
- Ren luyen kT nang giai thich cac hien tupng vat li ve dinh luat bao toan mdmen
ddnglupng.
- Ren luyen kT nang quan sat thi nghiem, thu thap thdng tin va xir li thdng tin.
II - CHUAN BI
Giao vien
- Chuan bi thi nghiem vdi ghe Giucdpxky : gom 1 ghe Giucdpxky va hai qua ta
tay loai 'ikg.
Hpc sinh
- On lai cac kie'n thiie vl ddng lupng va dinh luat bao toan ddng lupng d Vat li Idp
10 THPT.
III - THlfiT Kfi' HOAT D O N G DAY - H O C

Hoat d g n g cxla hgc sinh

Trg giiip cua giao vien

Hoat dgng 1
Kiem tra, chuan bj dieu kien
xuait phat. Dat vain de
HS suy nghT ca nhan tim cau tra Idi
M = I.y

F = ma

Momen lire M

Luc F

Gia tdc goc y

Gia tdc a

Momen quan tinh /

Khdi luang m

Dang khac ciia phuang trinh dinh
luat II Niu-ton : F = -^
At
24

trong dd

GV neu cac cau hdi kilm tra kiln thiic
cu:
- Neu su tuong tu giira hai phuang trinh
ddng luc hpc ciia chuyin ddng quay va
chuyin ddng tinh tien.

- Viet dang khac ciia phuong trinh dinh
luat II Niu-ton.


Hoat d g n g cua hgc sinh

Trg giiip cua giao vien

APla dp bie'n thien ddng lupng
trong khoang thdi gian At.
HS nhan thirc dupe va'n dl ciia bai
hpc.

Dgt van de : Khi viet phuang trinh dinh
luat II Niu-ton dang I ta cd thi tim dupc
su tuong tu giira phuang trinh dinh luat
II Niu-ton vdi phuong trinh ddng lire
hpc cua vat rin chuyin ddng quay
quanh mdt true. Cd sir tuang tu giira
phuang trinh ddng luc hpc ciia vat rin
chuyin ddng quay quanh mdt true vdi
phuang trinh dinh luat II Niu-ton dang
khac khdng? Bai hpc ngay hdm nay se

nghien ciiu dilu dd.

Hoat dgng 2
Xay dung khai niem mdmen
ddnglugng

GV neu cau hdi dl HS tim su tuong tu
giira phuong trinh ddng luc hpc cua vat
rin chuyen ddng quay vdi phuang trinh
dinh luat II Niu-ton dang khac

HS thao luan chung toan Idp dl tim
dang khac cua phuang trinh ddng
lire hpc ciia vat rin chuyin ddng
quay.

- Mud'n tim su tuong tu giiia phuong
trinh ddng luc hpc cua vat rin chuyin
ddng quay vdi phuong trinh dinh luat II
Niu-ton dang khac ta phai tim dupe
dang khac cua phupng trinh ddng luc
hpc cua vat rin chuyin ddng quay.
Dang khac ciia phuong trinh ddng lire
hpc cua vat rin chuyin ddng quay cd
dang nhu the nao ? Sir tuong tu ciia nd
vdi phuong trinh dinh luat II Niu-ton
dang khac la gi ?

Tacd M = Iy = 1 —
dt

Neu mdmen quan tinh khdng doi,
. ,,

.-'

»y

^(^^)

dL

dt

= —.
dt

ta CO the viet: M =

GV neu cac cau hdi gpi y:
- Viet bilu thiic dinh nghia gia tdc gdc.
- Ne'u mdmen quan tinh / khdng doi thi
cd thi viei phuong trinh ddng luc hpc cua
vat ran chuyin ddng quay nhu the nao ?

25


\

Hoat d g n g cua hgc sinh

Vay, ta cd sir tuong tu giiia hai
phuang trinh :
d(lco)
dt
Momen lire M
Dai luong L = lco

dt

1

Trg giiip cua giao vi§n
- Neu su tuang tu cua
ddng luc hpc cua vat rin
quay vira tim dupc vdi
dang khac ciia dinh luat II

phuang trinh
chuyin ddng
phuang trinh
Niu-ton.

Luc F
Dong lupng
p = mv

HS tilp thu, ghi nhd.

GV thdng bao:
- Phuang trinh M = — diing cho ca

dt
trudng hop mdmen quan tinh cua vat
hoac he vat thay doi.
- Dai lupng L = lo trong chuyen ddng
quay tuong ling vdi ddng lupng p = mv
trong chuyin ddng tinh tien. Vi the, ta
gpi L - lco la mdmen ddng lupng cua
vat rin dd'i vdi true quay.
- Don vi ciia mdmen ddng lupng la
kg.m Is.

Hoat dgng 3
Xay dung djnh luat bao toan
mdmen dgng lugng

GV neu cau hdi de HS xay dung dinh
luat bao toan mdmen ddng lupng

HS suy nghT ca nhan tim cau tra Idi

- Tim dilu kien dl mdmen ddng lupng
cua vat hoac he vat dupc bao toan.

Neu M = — = 0 =^ JZ = 0
dt
=> Z, = hing so
Ne'u tong cac mdmen lire tac dung
len mdt vat rin (hay he vat) dd'i vdi
mdt true quay bing khdng thi tong
mdmen ddng lupng cua vat (hay he

vat) ddi vdi true dd dupc bao toan.

26

GV neu cac cau hdi gpi y
- Ne'u mdmen ddng lupng L dupc bao
toan thi ddng bie'n thien cua mdmen
ddng lupng bing bao nhieu ?
- Tir phuang trinh M - — . tim dilu
dt
kien dl mdmen ddng lupng cua vat hoac
he vat dupc bao toan.