0. GV neu cau hdi de HS xay dung khai niem tdc dp gdc: - 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: - 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? - 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 ciia ti sd —^ khi A / tien dan tdi 0. At i^

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 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 yeu cau HS xay dung cdng thiic xac dinh tdc dp gdc tiic thdi va cho biet don vi cua tdc dp gdc. 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? 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 Hoat dong cua hoc sinh Trd giiip cua giao vien 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^ = cua vat ran trong khoang thai At gian At. HS thao luan chung toan Idp - Gia tdc gdc tire thdi d mdt thdi diem t dupe xac dinh bing gidi han , , . Aft) , , . » ..-J. - ,. r, cua tl so 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 xay dung cdng thiic xac dinh gia tdc gdc tiic thdi va cho bie't don vi cua gia tdc gdc. 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. Phuong trinh chuyen ddng ciia vat rin quay diu la : (p = (pQ + cot, trong dd q)Q la toa dp ban dau luc f = 0. 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. - 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 nhu vay chiing ta cd the vie't dupe phuang trinh chuydn ddng cho vat chuyfin ddng quay diu nhu the nao ? 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. 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 - Phuang trinh chuyen ddng quay bie'n ddi diu : 1 2

0). - Neu tdc dp gdc giam dan theo thdi gian thi chuyen ddng quay la cham din ir<0). 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 ? GV neu cac cau hdi gpi y: - 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 ? 11 Hoat dong ciia hoc sinh 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 • 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 I rco - rcOf) Aco • = - = r = ry Al At ; - Dp Idn cua vecto gia tdc toan ; phan dupe xac dinh ; / 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 a, Y • tana = - ^ = ^ - ; «« CO ; 12 Trg giup cua giao vien - 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 ? - Vecto gia tdc toan phin duoc xac dinh ; thdng qua hai thanh phan vecto gia tdc ; hudng tam va tiep tuye'n nhu the nao ? i Hoat dong cua hoc sinh 1 1 Hoat dong 7 Cling cd bai hpc va djnh hudng nhiem vu hoc tap tiep theo Trg giup ciia giao vien 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\=-R2- Cho 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 =^i = —(y2- B. &>2 = —2=9ft)|. D. 0)2=0}^. c) Kit luan nao sau day diing khi ndi vl tdc dp dai cua hai dilm ? 2 2 A. V, =-V2. B. V2--V,. C. V2=2v|. D. V2=3v]. BAI2 PHUONG TRINH DON G LUC HOC CUA VAT RA N QUAY QUANH M6 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 nang - 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 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. Trg giiip cua giao vien 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 dgng 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. O - ^ T, Luc F, gay ra gia tdc tie'p tuyen cho vat: F, = ma,. 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 : 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: - 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 ? - Luc tac dung theo phuang nao thi gay gia tdc tie'p tuye'n a, cho vat ? - Mdmen ciia luc F, dd'i vdi true quay O dupc xac dinh nhu the nao ? - 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 M = Y,M,= I 16 ( \ I / / nao ? Hoat dgng 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 HS thao luan chung toan lap va j dua ra du doan. • - Dai lupng ^^,7-, dac trung ; / '• cho miic quan tinh cua vat quay. | HS dua ra cac du doan : Du dodn I : Dai lupng ^ m,r, phu | thudc vao mdmen luc tie dung ; len vat rin va gia tdc gdc ma nd i \^ 2 M gayra : 2^m,r, = r I 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. - Can phai cd mdt vat rin, tac ; dung vao vat rin va do mdmen luc ; dd, do gia tdc gdc ciia vat rin. • Trg giiip cua giao vien 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 ? GV neu cac cau hdi gpi y: -Tirbilu 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 gia tri nhu the nao ?,Cd dl dang thay doi van tdc gdc cua vat rin hay khdng ? GV yeu cau HS thie't ke phuong an thi nghiem dl kilm tra cac du doan tren. GV gidi thieu bd thi nghiem va gpi y. 17 Hoat dgng 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 - 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 xac dinh: a^ ="V' tx Vay mdmen the xac dinh dupe gia tdc ciia qua gia trpng dupc khdng ? luc tac dung vao dTa trdn cd thi xac dinh : 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 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 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. 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. - 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 lupng Z»i,r,^ (viec xac dinh dai Trg giiip ciia giao vien - Can phai tien hanh thi nghiem nhu the nao dl kilm tra du doan 1. GV tien hanh thi nghiem dl kilm tra du doan thii nha't ciia HS. GV neu cau hdi vl thi nghiem can phai tiln hanh dl kiem tra du doan 2. - De kilm tra du doan 2 can phai tien 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, /?3 = 5cm. 19 Hoat dgng cua hgc sinh Trg giiip cua giao vien lupng ^m^ri 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. 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. 20 GV tien hanh thi nghiem. 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. Hoat dgng ciia hgc sinh Hoat dong 4 Van dung phuong trinh co ban ; ciia chuyen ddng quay ciia vat : rin de lam bai tap 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) : Mat khac, ta lai cd : y = —, thay • R • . ,ox - '. rr ly la '• vao (2) va rut ra : T = -^ = -—• • : R R^ : Thay T vao (1) ta dupc : j la ma - ma ; R^ mg 1 1 1,1 ^ \ m+ -^ \ + r- • R- mR^ ; Hoat dong 5 Cling cd bai hgc va dinh hudng : nhiem vu hoc tap tie'p theo Trg giiip cua giao vien Day la phuang trinh co ban ciia chuyin ddng quay ciia vat rin. GV yeu ciu HS lam viec vdi phieu hpc •• tap dl lam bai tap. 1 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 ? - GV yeu eau HS lam viec vdi bang 2.1 SGK dl tim sir tuong tu giira hai phuang 21 Hoat dgng 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 B. 0,75 kg.m^ D. 1,75 kg.m^ 22 A. 1,5 kg.m C. 0,5 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 TO AN 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 nang - 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 DON G DAY - HOC Hoat dgng 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 GV neu cac cau hdi kilm tra kiln thiic cu: M = I.y Momen lire M Gia tdc goc y Momen quan tinh / F = ma Luc F Gia tdc a Khdi luang m - Neu su tuong tu giira hai phuang trinh ddng luc hpc ciia chuyin ddng quay va chuyin ddng tinh tien. Dang khac ciia phuang trinh dinh luat II Niu-ton : F = -^ trong dd At 24 - Viet dang khac ciia phuong trinh dinh luat II Niu-ton. Hoat dgng cua hgc sinh APla dp bie'n thien ddng lupng trong khoang thdi gian At. HS nhan thirc dupe va'n dl ciia bai hpc. Hoat dgng 2 Trg giiip cua giao vien 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. Xay dung khai niem mdmen ddnglugng HS thao luan chung toan Idp dl tim dang khac cua phuang trinh ddng lire hpc ciia vat rin chuyin ddng quay. Tacd M = Iy = 1 — dt Neu mdmen quan tinh khdng doi, . , , .-' »y ^(^^) dL ta CO the viet: M = = — . dt dt 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 - 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 ? 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 dgng cua hgc sinh Vay, ta cd sir tuong tu giiia hai phuang trinh : d(lco) \ 1 Trg giiip cua giao vi§n - Neu su tuang tu cua phuang trinh ddng luc hpc cua vat rin chuyin ddng quay vira tim dupc vdi phuang trinh dt Momen lire M Dai luong L = lco dt Luc F Dong lupng p = mv dang khac ciia dinh luat II Niu-ton. HS tilp thu, ghi nhd. Hoat dgng 3 Xay dung djnh luat bao toan mdmen dgng lugng HS suy nghT ca nhan tim cau tra Idi 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 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. GV neu cau hdi de HS xay dung dinh luat bao toan mdmen ddng lupng - Tim dilu kien dl mdmen ddng lupng cua vat hoac he vat dupc bao toan. 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. Hoat d6ng cua hgc sinh Vi mdmen ddng lupng dupc bao toan ne n : I\COi = I2CO2. HS thao luan chung toan Idp. - Can phai cd mdt vat rin, thay doi tdc dp gdc hoac mdmen quan tinh cua vat, do / va co tuong irng. Sau dd tinh tich : lco. Ne'u mdmen ddng lupng cua vat dupe bao toan thi tich lo) = hing sd. HS chu y quan sat. HS thao luan chung toan Idp. - Can phai truyin cho he vat gdm ngudi va dia quay mdt tdc dp gdc, thay doi mdmen quan tinh ciia he bing each dang hai tay cam ta hoac CO hai tay cam ta lai. Quan sat su thay doi tdc dp gdc ciia he vat. HS chii y quan sat va rut ra kei luan. - He vat da dupe truyen mdt tdc dp gdc, khi dang hai tay cam ta ra thi mdmen quan tinh tang, tdc dp gdc Trg giiip cua giao vien GV neu cau hdi dl HS thiei ke phuang an thi nghiem kilm nghiem lai dinh luat bao toan mdmen ddng lupng. - Thiei ke mdt phuang an thi nghiem dl kilm nghiem lai dinh luat bao toan mdmen ddng lupng. GV gidi thieu bd thi nghiem vdi ghi Giucdpxky. - Ghe Giucdpxky la mdt dTa kim loai cd thi quay quanh mdt true cd phuang thing diing tren mdt de nam ngang. GV neu cau hdi cho HS tien hanh thi nghiem vdi ghe Giucdpxky: - Cho mdt ban cam hai qua ta tren hai tay va diing len ghe, can phai tien hanh thi nghiem nhu the nao dl kilm nghiem mdt each dinh tinh dinh luat bao toan mdmen ddng lupng? GV cho 2 HS tien hanh thi nghiem. 27 Hoat dgng cua hgc sinh Trg giiip cua giao vien ciia he vat giam. Ngupc lai, khi co hai tay cam ta lai, mdmen quan tinh cua vat giam, tdc dp gdc cua he vat tang. Hoat dgng 4 Cling cd bai hgc va dinh hudng nhiem vu hgc tap tie'p theo HS lam viec ca nhan, sau dd thao luan chung toan Idp. Vay, mdt each dinh tinh, chiing ta da kilm nghiem dupc dinh luat bao toan ddng lupng la diing. - GV yeu ciu HS lam bai tap trong phieu hpc tap. - HS vl nha lam cac bai tap cdn lai trong SGK. - On lai eac kie'n thiic vl ddng nang va dd bie'n thien ddng nang da hpc d Vat 11 10 THPT. PHIEU HOC TAP Cau 1. Mdt vat cd mdmen quan tinh 0,12kg.m^ quay diu 10 vdng trong \,%s. Mdmen ddng lupng ciia vat cd dp Idn bing A. 4 kg.m^ls. B. 8 kg.m^ls. C. 13 kg.m^/s. D. 25 kg.m^/s. Cau 2. Hai dia trdn cd mdmen quan tinh /, va I2 dang quay ddng true va eiing chilu vdi tdc dp gdc ffl] va CO2 nhu hinh ben. Ma sat d true quay nhd khdng dang kl. Sau dd cho hai dTa dinh vao nhau, he hai dTa quay vdi tdc dp gdc co. c6 dp Idn dupe xac dinh bang cdng thiic "(oTijjH;); 'llll;, . 0)-, hii? /, « ] \ ""/, I l l A. CO- h+h /]ft>i + I2CO2 1]Q)2 + l2(0\ B. (y - 1\<^\ + ^2'^2 /1+/ 2 IyCOi-l20}2 28 C. co = /,+/ , D. CO-- l,+l2 Cau 3. Mdt vat rin cd mdmen quan tinh Ikg.m"^ quay diu 10 vdng trong 2s. Mdmen ddng lupng ciia vat rin cd dp Idn bing A. 3,l4lkg.m^/s. B. 3l,4lkg.m'^/s. C.3l4,lkg.m'^/s. D.3l4lkg.m^/s. BAI4 DONG NANG CUA VAT RAN QUAY QUANH MO T TRUC c 6 BJNH I - MUC TifeU 1. Ve kien thiic - Biei dupe khi mdt vat rin quay (quanh mdt true) thi vat cd ddng nang. - Biei so sanh dai lupng tuong ling trong bilu thiic eiia ddng nang quay va ddng nang trong chuyin ddng tinh tien. - Hiiu va ap dung dupe dinh luat bie'n thien ddng nang cua vat rin trong chuyin ddng quay. - Giai cae bai toan don gian ve ddng nang ciia vat rin trong chuyin ddng quay. - van dung kie'n thiie dl giai thich mdt sd hien tupng trong thue te, biet cac ling dung ciia ddng nang quay trong kT thuat. 2. Ve kl nang - Ren luyen kT nang Idgic toan hpc dl tim bilu thitc ddng nang cua vat rin trong chuyin ddng quay. - Ren luyen kT nang giai thich cae hien tupng vat li vl ddng nang cua vat rin. - Ren luyen kT nang giai cac bai toan vl ddng nang va dp bie'n thien ddng nang ciia vat rin quay. II - CHUXN BI Giao vien - Ve hlnh 4.1 SGK, philu hoc tap. Hpc sinh - On lai cac kie'n thitc ve ddng nang va dp bie'n thien ddng nang da hpc d Vat li 10 THPT. 29 Ill - THifeT K£' HOAT DON G DAY - HOC Hoat dgng ciia hgc sinh Hoat dgng 1 Kiem tra, chuan bi dieu kien ; xuat phat. Dat van de HS suy nghT ca nhan, sau dd thao ; luan chung toan Idp. : - Trudng hpp may mai quay nhanh ; thi dTa may se cd nang lupng Idn : hon vi cd kha nang sinh cdng lam | mai mdn cae vat va gay ra su toa • nhiet... • Ca nhan nhan thirc dupe van dl | ciia bai hpc. • Hoat dgng 2 Xay dung bieu thiic tinh dgng | nang cua vat rdn quay quanh ; mgt true cd dinh HS suy nghT ca nhan. i 30, Trg giiip cua giao vien GV neu cau hdi kiem tra kie'n thiic cu: - So sanh nang lupng ciia dTa may mai trong hai trudng hpp : may mai quay nhanh va may mai quay cham. Dgt van de : Nang lupng cua dTa may mai khi quay gpi la ddng nang cua vat rin (dTa mai) quay quanh true cd dinh. Bilu thiic tinh ddng nang cua vat rin quay quanh true cd dinh dupc xac dinh nhu the nao ? Bai hpc ngay hdm nay giiip chiing ta xay dung bilu thiic dd. GV yeu cau HS tim bieu thu:c tinh ddng nang ciia vat rin quay quanh mdt true CO dinh. A' ^ y ^ ] / ^ V 1 m, \ 1 Hoat dgng cua hgc sinh Cac chai dilm chuyin ddng quay vdi ciing tdc dd gdc, ddng nang cua mdt chat dilm dupe xac dinh : -w,v,. =-m,{cor^) Ddng nang cua vat rin bing tong ddng nang cua cac chat dilm cau thanh vat: ^^ V / \2 1, 2 Hoat dgng 3 Xay dung bieu thurc ciia djnh If bien thien dgng nang ciia vat ran quay quanh mgt true cd djnh HS suy nghT ca nhan. HS lam viec ca nhan vdi phieu hpc tap. Cdng cua ngoai luc la : A = Fs^ FRcp Mat khac M = FR = I.y => /4 = lycp. Ma ta lai co; 0)2-0)^ - 2Ycp ^A = -lcol—lco? = AW 2^2 ' Trg giiip cua giao vien GV neu cac cau hdi gpi y: - Coi vat rin gdm nhilu chat dilm, mdi chat dilm cd khd'i lupng m; va each true quay mdt khoang /•;. Van tdc gdc ciia cac chat dilm nay cd dac dilm gi ? - Ddng nang ciia mdi chat dilm dupe xac dinh nhu the nao ? - Ddng nang cua vat rin dupe xac djnh nhu the nao ? GV neu cau hdi vl van dl can nghien ciru: - Khi vat rin quay quanh mdt true cd dinh chiu tac dung cua ngoai luc F khdng doi va ludn tiep tuyen vdi quy dao dilm dat thi ddng nang cua vat rin thay doi. Dp bie'n thien ddng nang ciia vat rin dd cd quan he nhu the nao vdi cdng cua ngoai luc F ? Bilu thiic toan hpc nao bilu thi mdi quan he dd ? GV neu cac cau hdi gpi y: - Yeu eau HS lam viec vdi phieu hpc tap dl tra Idi cau 1. - Cdng cua luc F dupe xac dinh nhu the nao ? - Cdng ciia lire F cd quan he nhu the nao vdi mdmen ciia luc F ? - Viei bilu thii'c lien he giiia tdc dp gdc, gia tdc gdc va dp bie'n thien toa dp gdc. 31 Hoat dgng cua hgc sinh HS tilp thu, ghi nhd. Hoat dgng 4 Ap dung cdng thurc tinh dgng nang ciia vat ran quay quanh mot true cd dinh de lam bai tap HS lam viec ca nhan vdi phieu hpc tap. Ddng nang liic diu cua vat la : f^d(dau)=^/l^'=202,5J. Vi mdmen lire tac dung vao van ddng vien bing 0 nen theo dinh luat bao toan mdmen ddng lupng, ta cd : /| 6^2 = 3^1 Ddng nang luc cud'i la: f^d,cu6i)=^/2^2'=^y(3^l'f = 3.^d(dau)=607,5J. Hoat dgng 5 Cling cd bai hgc va dinh hudng nhiem vu hgc tap tiep theo 32 Trg giup cua giao vien GV thdng bao: - Bilu thiic A = -Io)j--lo}? =AW la 2 ^ 2 bilu thiie ciia dinh li bie'n thien ddng nang. - Dinh li bie'n thien dgng ndng : Dd bie'n thien ddng nang cua mdt vat bing tdng cdng cua cae ngoai lire tac dung vao vat. GV yeu cau HS lam viec vdi phieu hpc tap dl lam bai tap 2. GV neu cac cau hdi gpi y: - Xac dinh ddng nang bing cdng thirc nao ? Ddng nang ban diu dupc xac dinh nhu the nao ? - Mud'n xac dinh dupc ddng nang liic cud'i can phai xac dinh dupc dai lupng nao ? - Theo dinh luat bao toan mdmen ddng lupng, ta cd thi tinh dupc tdc dp gdc liic cud'i nhu the nao ? GV yeu cau hpc tim su tuang tu giira bilu thiic ddng nang ciia vat rin quay Hoat ddng cua hgc si^h HS lam viec ca nhan, sau dd thao luan chung toan Idp. Trg giiip cua giao vien quagh mgt true cd dinh vdi bilu thu'c ddng nang cua vat chuyin ddng tinh tig'n va lam cae bai tap cdn lai trong phieU hpc tap. - Vl nha lam cac bai tap trong SGK. - On cac kie'n thiic, eac cdng thiic va ,phuang trinh ddng lire hpc cua chuyin ddng quay. - On lai phuang phap ddng lire hpc da hoc d Idp 10 THPT. PHil^U HOC JAP Cau 1. Mdt vat rin chiu iac dung cua mdt luc F cd dp Idn khdng doi va ludn ludn tiep tuye'n vdi quy dao chuyin ddng cita dilm dat. Trong qua trinh chiu F tac dung, vat rin quay dupc mdt gdc g) thi tdc dp gdc thay doi tir coy de'n co2.T{nh cdng cua ngoai luc F theo tdc dp gdc va mdmen quan tinh cua vat rin. Cau 2. Mdt van ddng vien trupt bang quay quanh mdt true thing dung vdi tdc dp gdc 15 radls vdi hai tay dang ra, mdmen quan tinh ciia ngudi liic nay ddi vdi true quay la 1,8 kg.m Sau dd ngudi nay ddt ngpt thu tay lai dpc theo than ngudi, trdng khoang thdi gian nhd tdi miic cd thi bd qua anh hudng cua ma sat vdi mat bang. Mdmen quan tinh cua ngudi liic dd giam di ba lin so vdi liic dau. Tinh ddng nang cua ngudi dd liic dau va luc cuoi. Cau 3. Hai vat rin cd cung mdmen quan tinh va cd ddng nang lien he vdi nhau theo bieu thiic W^ ^2W^ . Kei luan nao sau day diing khi ndi vl tdc dp gdc ciia hai vat rin ? A. ^1 Oh, 3 B. £y, CO-, 3 2 ^•^= - D. (0^ =C02. 33 BAI5 BAl TAP wt D6NG Lire Hpc VAT RAN I - MUC TifiU 1. Ve kien thiic - Luyen tap van dung cac cdng thiic va phuang trinh ddng luc hpc cua vat rin chuyin ddng quay. - Luyen tap van dung cdng thiic tinh ddng nang quay cua vat rin. 2. Ve ki nSng - Ren luyen cho HS kT nang van dung linh hoat cac cdng thiic va phuang trinh ddng lire hpc cua chuyin ddng quay dl giai cac bai tap co ban. II - CHUAN BI Giao vien - Du kie'n cac sai lam (vl kie'n thiic va phuang phap) ma HS cd thi mic phai khi giai bai tap. - Chuin bi phieu hpc tap cho HS. Hpc sinh - On cac kie'n thiic, cae cdng thirc va phuong trinh ddng lire hpc cua chuyen ddng quay dl cd thi giai dupc cac bai tap vi du dudi sur gpi y cua GV. - On lai phuang phap ddng lire hpc d Idp 10. III - THlfiT Kfi' HOAT D6N G DAY - HOC Hoat dgng cua hgc sinh Hoat dgng 1 Kiem tra, chuan bj dieu kien xua't phat 34 Trg giiip cua giao vien GV neu cau hdi kilm tra kie'n thiic cu: - Viet cdng thiic dinh nghTa gia tdc gdc ciia vat rin chuyen ddng quay ? Hoat ddng cua hgc sinh Trg giiip cua giao vien HS suy nghT ca nhan tim cau tra Idi. Hoat dgng 2 Lam bai t$p 1 de dn tap lai cac kien thurc da hgc ve chuyen dgng quay ciia vat ran quanh mgt true. HS lam viec ca nhan sau dd thao luan chung toan Idp. a) Gia tdc gdc cua banh xe dupc xac dinh: - Giai doan quay nhanh din deu : - Viei phuang trinh ddng lire hpc ciia vat rin quay quanh mdt true cd dinh ? - Viet cdng cdng thirc tdc dp gdc va phuang trinh chuyin ddng cua vat rin quay quanh mdt true cd dinh ? GV yeu cau HS lam viec vdi phieu hpc tap dl lam bai tap 1. GV neu cac cau hdi gpi y: - Ap dung cdng thiic nao dl tinh gia tdc gdc ? 10 Ar, = \,5radl s^ - Trong giai doan dau van tdc gdc bie'n - Giai doan quay cham dan diu 0)2-Q}\ _ 0 -15 At. 30 72 -0,5rad/s^ b) Mdmen quan tinh cua banh xe dd'i vdi true quay Tong mdmen tac dung vao banh xe d giai doan quay nhanh dan deu: M = M,+M,, = Mi+i-0,25M^)^l5N.m ^ = ioW thien nhu the nao ? - Khoang thdi gian xay ra bie'n thien dd bing bao nhiSu ? - Ap dung cdng thiic nao dl tinh mdmen quan tinh cua vat rin dd'i vdi true quay ? - Trong phuang trinh ddng luc hpc ciia vat rin chuyin ddng quay quanh mdt true, dai lupng nao da biei, dai lupng nao chua biet ? - Dl biet dupc gia tdc gdc trong phuang trinh, ta can phai viei phuang trinh ddng lire hpc cua vat rin trong giai doan nao ? - Trong giai doan dd, mdmen dupc xac dinh nhu the nao ? Cd miy mdmen lire tac dung vao vat trong giai doan dau? - Mdmen tong hpp dupe xac dinh nhu the nao ? 35 _ ^ ^ Hoat dgng cua hgc sinh c) Ddng nang quay ciia banh xe d j diu giai doan quay cham dan diu: IV. =-Ico? =-.20.15^ =\\25J. \ 2 2 ; Hoat dgng 3 Lam bai tap 2 de bie't each ap ; dung phuong trinh ddng luc hgc \ cua vat ran quay HS lam viec ca nhan sau dd thao | luan chung toan Idp • a) Mdmen ham M - ly, trong dd : ; / la mdmen quan tinh cua dTa trdn ; ddng chat, nen : I =-mR^=-.1.0,2^ ^0,02kg.m^ '• 2 2 \ Gia tdc gdc : : Aco 0-10 . ,, 2 i / = = = -5rad 1 s ; At 2 ; Vay mdmen ham : | M = 0,02.(-5) = -0,lN.m b) Thdi gian dTa quay de'n khi | dirng han Tir cdng thiic ; co = o)Q+yt CO-On 0-1 0 - => t = = = 2s. ; r -5 ; 36 Trg giiip cua giao vi§n - Ap dung cdng thu'c nao dl tinh ddng nang quay ciia vat rin ? GV yeu cau HS lam viec vdi phieu hpc tap dl lam bai tap 2. GV neu cac cau hdi gpi y: - Mdmen quan tinh cua dTa trdn ddng chat dupc xac dinh nhu the nao ? - Dl tinh dupc mdmen ham, ta can phai tinh them dai lupng nao niia ? Hoat ddng cua hgc sinh Trg giiip cua giao vien Hoat dgng 4 Tim hieu khai niem he quy chieu va chuyen ddng tjnh tien HS lam viec ca nhan sau dd thao luan chung toan Idp. a) Tinh gia tdc gdc cua rdng rpc 1 2 2fi) Tir cdng thuc cp^ — yt ^/-— - 2 2.4n = 6,2^radls' Thay sd : y =• b) Gia tdc ciia hai vat a^Ry =0,1.6,28«0,63w/5^. GV yeu ciu HS lam viec vdi philu hpc tap dl lam bai tap 3. - Ap dung cdng thiic nao dl tinh gia tdc gdc eiia rdng rpc ? - Viei phuang trinh chuyin ddng ciia vat rin quay quanh mdt true ? - Gia tdc cua vat A va B lien he nhu the nao vdi gia tdc tiep tuye'n cua rdng rpc ? B - <: ZL Cv Y. A^T, - Viet cdng thirc lien he giira gia tdc tie'p tuyln vdi gia tdc gdc ciia rdng rpc ? c) Tinh luc cang cua spi day d hai ben rdng rpc - Xet vat A; P -T^ = ma Suy ra: T^ = P - ma = m(g - a) Thay so : TA= 1(9,8-0,628)« 9,17N - Xet rdng rpc : - Phan tich luc tie dung vao cac vat va vao rdng rpc ? - Viet phuang trinh chuyin ddng cho vat A? - Luc cang T^ va Tg cd dd Idn bing nhau khdng ? Tai sao ? - Tong hpp mdmen luc tie dung vao rdng rpc bing bao nhieu ? Cd bing 0 37 Hoat dgng cua hgc sinh Trg giiip cua giao vien {TA-TB)-I^^TB=T,-1^ Thay sd: To = 9,17-0,05. 6,28 0,1 = 6,03A^. d) Vi Tg - 6,03N > ma, suy ra giiia vat B va ban ed ma sat, dp Idn cua luc ma sat dupc tinh nhu sau : - Xet vat B : TH - Fm., = ina Suy ra : F^^ = TB-ma = 6,03-1.0,628 « 5,4/V. He sd ma sat giira vat B va mat ban la M mg 5,4 1.9,8 = 0,55. Hoat dgng 5 Cung cd' bai hgc va dinh hudng nhiem vu hgc tap tiep theo khdng ? Tai sao ? - Mdmen luc tong hpp tac dung vao rdng rpc dupe tinh nhu the nao ? - Viet phuang trinh chuyen ddng cua vat rin la rdng rpc ? - Cd luc ma sat giira vat B va mat ban khdng ? Tai sao ? - So sanh dd Idn cua luc cang Tg vdi tich ma ? Cd ket luan gi vl dilu nay ? - Luc ma sat dupe xac dinh nhu the nao ? - Viet phuang trinh dinh luat II Niu tan cho vat B ? GV hudng din HS tim hiiu sir tuong tu giQa cac dai lupng gdc dac trung chuyin ddng quay va dai lupng dai dac trung cho chuyin ddng thing d phin tdm tit chuang I. - On lai vl dao ham, each tinh dao ham, y nghTa vat li cua dao ham. PHIEL HOC TAP Cau 1. Mdt banh xe dap chiu tic dung ciia mdt mdmen luc M, khdng doi la 20/V.m. Trong 10^ dau, tdc dp gdc cua banh xe tang deu tir 0 de'n \5radts. Sau dd mdmen M, ngtoig tac dung, banh xe quay cham dan diu va dimg 38 hin lai sau 30i'. Cho biet mdmen ciia luc ma sat cd gia tri khdng ddi trong sudt thdi gian banh xe quay va bang 0,25JV/,. a) Tinh gia tdc gdc cua banh xe trong cac giai doan quay nhanh din diu va quay cham dan diu. b) Tinh mdmen quan tinh cua banh xe dd'i vdi true. c) Tinh ddng nang cua banh xe d dau giai doan quay cham din d6u. Cau 2. Mot dia trdn ddng chat khd'i lupng m = I kg, ban kinh R - 20cm dang quay diu quanh mdt true vudng gdc vdi mat phang dTa vdi tdc dp gdc COQ =\OradlS. Tac dung len dia mdt mdmen ham. DTa quay cham dan diu va dumg han sau khi da quay dupe mdt gdc \Orad. a) Tinh mdmen ham dd. b) Tinh thdi gian tir liic chiu tac dung ciia mdmen ham de'n khi dTa dimg hin. Cau 3. Hai vat A va B cd ciing khdi lupng m= \kg, dupe lien kei vdi B IZZ. nhau bing mdt spi day nhe, •"•'' 'i . i • •[ khdng gian, vit qua rdng rpc cd ban kinh 10cm va mdmen quan tinh / = 0,050kg.m^ Biet day khdng trupt tren rdng rpc nhung khdng biei giiia vat B va ban cd ma sat hay khdng. Liic dau eac vat dupe giii diing yen, sau dd he dupc tha ra. Ngudi ta thay sau 2s, rdng rpc quay quanh true cua nd dupc 2 vdng va gia tdc ciia cac khd'i A, B khdng doi. Cho g = 9,Sm/s^ Coi ma sat d true cua rdng rpc khdng dang kl. a) Tinh gia tdc ciia rdng rpc. b) Tinh gia tdc ciia hai vat. c) Tinh luc cang cua day d hai ben cua rdng rpc. d) Cd ma sat giiia vat B va mat ban hay khdng. Neu cd, hay tinh he sd ma sat. 39 B Al KlfiM TRA CHUONG I I - MUC TifiU - Ciing cd, khic sau kie'n thiic d chuang I. - Ren luyen diic tinh trung thue, can cii, cin than, chinh xac, khoa hpc. Phat huy kha nang lam viec ddc lap d I^S. II - CHUXN BI Giao viSn - Dl bai kilm tra theo miu. Hpc sinh - Kiln thiic toan chuang I. Ill - THifi'T Kfi' PHUONG A N DAY HOC Hoat dgng cua hgc sinh Hoat dgng 1. On djnh idp Hoat dgng 2. • • Lam bai kiem tra Hoat dgng 3. Tong ke't gid hgc. 40 Trd giup cua giao vien GV kilm tra sT so HS va neu yeu ciu vl ki luat dd'i vdi gid kiem tra. GV phat bai kilm tra tdi tirng HS. t^uaa I( HS lam bai, dam bao tinh ediig bang, trung thuc trong khi lam bai. GV thu bai va nhan xet vl ki luat gid hpc. NOI DUNG KIEM TRA I - BAI TAP TRAC NGHIEM 1. Khoanh tron trudc dap an ma em lua chgn (Chu y : mdi cdu chi duac lua chgn mgt ddp dn). Cau 1. Kei luan nao sau day diing khi ndi vl chuyin ddng cua mdt dilm tren vat rin quay quanh mdt true cd dinh ? Khi vat rin quay A. eac dilm khac nhau tren vat rin quay vdi tdc dp gdc khac nhau trong cimg mdt khoang thdi gian. B. mdi dilm tren v&t rin vach mdt dudng trdn nim trong mat phing vudng gdc vdi true quay. C. cac dilm khac nhau tren vat rin quay dupc cac gdc khac nhau trong eiing mdt khoang thdi gian D. mpi diem tren vat rin cd ciing mdt tdc dp dai Cau 2. Mdt dTa CD quay diu vdi tdc dp quay 450 vdng/ phiit trong mdt 6 dpc cua may vi tinh. Tdc dp gdc cua dTa CD dd tinh theo rad/s la A. 410radls. B. 41 radls. C. 4,lradls. D. 0,41radls. Cau 3. Mdt vat bit dau quay diu quanh mdt true cd dinh, sau 2s dat dupc tdc dp gdc lOrad/s. Gia tdc trung binh cua vat trong thdi gian dd la A. 5radls^ B. lOrad/s'^ C.\5radls^ D.25radls^ Cau 4. Mdt diem tren vat rin each true quay mdt doan R. Khi vat rin quay diu quanh true vdi van tdc gdc co thi tdc dp dai cua dilm dd la A. v = —• B. v = —• R : CO C. V = CO.R\ D . V = CO.R. 41 Cau 5. Gia tdc tie'p tuye'n ciia mdt dilm tren vat rin quay khdng diu dupe xac dinh bdi cdng thiic A. a, = —• 7 C. a, =^ - B. o, = ry. D. a, = ry^ Cau 6. Mdt thanh kim loai khd'i lupng m cd tiei dien nhd so vdi chilu dai / cua nd. Mdmen quan tinh cua thanh kim loai so vdi true quay A di qua dilm giiia cua thanh la A/ ^ -> -t A. I = —(ml) 12^ ^ C. l = — m^l 12 B. / = 12/«/i D. I = ^mll 12 Cau 7. Phuang trinh chuyin ddng quay bie'n ddi diu cua vat rin quanh mdt true cd dinh cd dang : ^ = 3 -i- 2r + 6f (cp; rad, t: giay). Gia tdc gdc tii'c thdi ciia vat rin tai thdi dilm r = 35 A. 36rad/s C. \2radls B. 3Srad/s' D. 25radls^ Cau 8. Mdt vat nang khd'i lupng 25kg dupc budc vao mdt spi day mIm vit qua mdt rdng rpc cd dinh cd ban kinh 0,05m. Dau kia cua spi day chiu tac dung cua mdt luc 245/V. Bd qua cac ma sat va khd'i lupng ciia rdng rpc. Mdmen luc tong hpp dd'i vdi true quay ciia rdng rpc la (cho g - 9,?>mls ) . A. 0. B. 5/V.m. C. -2,5N.m. D. 4,5/V.m. • 25kg F=245N Cau 9. Phuong trinh ddng luc hpc eiia vat rin quay quanh mdt true la A. M = 1Y. B. M = 1Y^ C. M = PY. D. M=-Iy\ 2 ' 42 Cau 10. Chpn phuang an sai. Tac dung vao vat rin cd true quay cd dinh mdt mdmen luc khdng thay ddi thi A. mdmen quan tinh khdng thay ddi. B. khd'i lupng ciia vat khdng thay ddi. C. gia tdc gdc khdng thay ddi. D. tdc dp gdc khdng thay ddi. Cau 11. Td hpp don vi co ban nao dudi day la dan vi do mdmen ddng lupng trong he 5/ ? A. kg.m .s B. kg.m .s C. kg.m .s. D. kg.m .s Cau 12. Mdt vat chiu tac dung mdt luc F = lOON tai mdt dilm A' each true quay mdt doan 2m theo phuong tie'p tuye'n vdi quy dao chuyin ddng cua dilm N. Mdmen luc tac dung vao vat cd gia tri A.M = 50N.m. B. M = iOON.m. C.M = 200/V.m. D. M = 250N.m. Cau 13. Dd thi ham sd nhu hinh ve ben bieu diln 'P^ sir phu thudc cua tdc dd gdc ciia vat rin quay diu vao thdi gian. Kit luan nao sau day diing khi ndi vl gdc 6* tren dd thi ? A. 0 = 0). B. tane = CO. C. tan6' = ^o- D. tan0 = y- — = — = 6rad/s^ Mat khac mdmen luc tac dung len vat rin dupc xac dinh : M^F.d = ly=>l = — ^ ^^^^ = 0,04kg.m^ 7 6 b) Ap dung cdng thiic : co = co^^ + yt = 0 + 6.10 = SOrad / s. c) Tai thdi dilm r, = lOs, vat rin khdng chiu tac dung ciia lire F nen M = 0, suy ra/ y = 0=^ y-0. Vay vat rin chuyin ddng quay diu vdi tdc dp gdc bing 60rad/s. - Dl tinh toa dd gdc tai thdi dilm ^2 = 20s, ta tinh gdc quay ^| eiia vat rin trong qua trinh vat rin quay nhanh din diu trong khoang thdi gian r, = lOs va gdc quay (92 cua vat rin trong qua trinh vat rin chuyin ddng quay diu trong khoang thdi gian ^2 - 'i = 20 -10 =10i. Toa dp gdc eiia vat rin tai thdi dilm ^2 = 20^ la : (p = (p]+ cp2. Tacd : cp^ =cp^ + ci}^t + -yt^ ^-yt'^ =-.6.10^ =300raa' ^2=fi;/ = 60.10 = 600ra6? Suy ra: cp = cp]+cp2= 300 + 600 = 900rad. Bai 2. a) Tinh mdmen ddng lupng va ddng nang cua he gdm ngudi va ghe. - Ap dung cdng thiic tfnh mdmen ddng lupng cua he : 45 I, =ft>,/, =10.5 = 50^g.m^/5. - Ap dung cdng thiic tinh ddng nang ciia he : W, =-/,« ? =-.5.10^=2507. ' 2 ' ' 2 b) Vi bd qua mpi luc can, trpng luc cua ngudi va ghe can bang vdi phan luc nen tdng mdmen luc tac dung vao he bing 0. Suy ra tdng mdmen ddng lupng eiia he dupc bao toan => I) = Z-2 => ^1^1 = -^2^2 => ^2 7,6;, _5.10 = 6,25rad I s. Suy ra ddng nang ciia he sau khi da dang tay la Wj =-/26)2^ =-.8.6,25^ =156,25J. ^ 2 ^ ^ 2 BliuDI^MD^l I - BAI TAP TRAC NGHlfiM 0,25 dilm/cau x 16 cau = 4 diem. I I -BA I TAP TU LUAN Bai 1. (3,5 dilm) Xac dinh gia tri y : 0,5 dilm. Xac dinh gia tri 7 : 1 diem. Xac dinh gia tri co : 0,5 dilm. Xac dinh tdc dp gdc tai r, = \0s : 0,5 diem. Vilt bilu thiic toa dp gdc tai ^2 = 20s : 0,5 dilm. Tinh gia tri cp : 0,5 diem. Bai 2. (2,5 dilm) Tinh gia tri md men ddng lupng cua he : 0,5 diem. Tinh gia tri ddng nang cua he : 0,5 dilm. Tinh gia tri CO2 '• I dilm. Tinh gia tri ddng nang khi da dang tay : 0,5 dilm. 46 De2 I - BAI TAP TRAC NGHIEM 1. Khoanh tron trudc dap an ma em lua chgn (Chu y : mdi cdu chi duac lua chgn mgt ddp dn). Cau 1. Mdt vat rin cd dang hlnh cau dac ddng chat ban kinh R - 0,5m quay diu quanh true quay di qua tam vdi tdc dd gdc bing 50rad/s. Ddng nang cua vat rin bing 1257. Khd'i lupng cua vat rin nhan gia tri nao trong cac gia tri sau A. 0,5kg. B. \kg. C. \,5kg. D. 2kg. Cau 2. Phat bilu nao dudi day diing ? Vi tri khd'i tam ciia mdt vat phu thudc vao 1) dang hlnh hpc cua vat rin. 2) phan bd khd'i lupng trong vat rin. 3) khd'i lupng cua vat rin. A. chi I). B. chi 2). C. cai) lin 2). D. chi 3). Cau 3. Mdt ngudi ngoi tren mdt chiec ghe quay, hai tay cam hai qua ta gidng nhau de trudc nguc ; khi dang quay ngudi ay dang tay ra, neu bd qua ma sat anh hudng de'n su quay thi chuyin ddng quay se A. dimg lai. B. quay nhanh len. C. khdng thay ddi. D. quay cham lai. Cau 4. Hai vat rin cd ciing mdmen quan tinh va cd ddng nang lien he vdi nhau theo bieu thiic W^ = 2W^ . Kei luan nao sau day diing khi ndi vl tdc dp gdc cua hai vat rin ? A. 6 ^ _ 2 CO2 3 2 C. =6)2 D. CO] =0)2. 47 Cau 5. Mdt vat rin cd mdmen quan tinh 2kg.m^ quay vdi tdc dp gdc \00rad/s. Ddng nang quay ciia vat rin la A. 2007. B. 100007. C. 400/. D. 20000J. Cau 6. Dan vi nao khdng phai la don vi ciia van tdc gdc. A. vdng/giay (vg/s). B. met/giay (m/s). C. vdng/phiit (vg/min). D. radian/giay (rad/s). Cau 7. Tdng mdmen ddng lupng cua vat rin dupc bio toan khi tdng mdmen luc tac dung vao vat rin bing A. hing sd. B. vd cimg. C. mdt sd bit ki. D. khdng. Cau 8. Mdt banh xe quay cham din diu quanh mdt true cd dinh vdi van tdc gdc ban diu la 1,5rad/s. Sau 2s banh xe dirng lai, gia tdc gdc ciia xe la A. 3 rad/s^ B.4,\5rad/s' C. 3,25rad/s^ D. 3,15rad/s^ Cau 9. Bilu thiic nao trong cac bilu thiic sau day bilu diln dinh luat bao toan mdmen ddng lupng ciia he vat cd mdmen quan tinh thay ddi ? A . I\CO]= l2(02- CO] CO2 C.^ = ^ CO, &>2 D . 1]C0] = I2CO2. Cau 10. Mdt vdng du quay ban kfnh 4m dang quay diu vdi van tdc gdc 1,5;T rad/s. Gia tdc cua ngudi dd la A. 80,5m/s^ B. 88,7m/s^ ..2 r. ^ ^ . , 2 C. 78,6m/s D. 90,3m/s' Cau 11. Luc dl lam quay canh cua (Hinh ve) dupc dat tai dilm M lin lupt theo cac phuong 1, 2, 3, 4 ; cac phuang nay cung nim trong mat phing vudng gdc vdi canh cua. OM la giao tuyen cua canh cira vdi mat phang nay. 48 Cho biei : 0M3 < OMl = 90° < 0M4 < 0M2 . Luc se cd cudng dp nhd nhit khi dat theo A. phuong 1. B. phuang 3. C. phuang 4. D. phuang 2. Cau 12. Mdt vat rin dang quay nhanh din diu quanh mdt true ed dinh xuyen qua vat thi A. tich van tdc gdc va gia tdc gdc la mdt sd am. B. gia tdc gdc ludn ludn cd gia tri duong. C. tfch van tdc gdc va gia tdc gdc la mdt so duang. D. van tdc gdc ludn cd gia tri duong. Cau 13. Mdt vat rin cd mdmen quan tinh dd'i vdi mdt true la /. Vat rin dang quay vdi van tdc gdc o) quanh true quay dd. Coi ma sat d true quay la khdng dang kl. Ne'u tdc dp gdc cua vat tang len 2 lin thi ddng nang cua vat A. tang len 2 lin. B. tang len 4 lan. C. giam 2 lin. D. khdng thay ddi. Cau 14. Hai vat rin ed ciing mdmen quan tinh va cd ddng nang lien he vdi nhau theo bilu thirc W^ = 2W^ Kit luan nao sau day diing khi ndi vl tdc dp gdc cua hai vat rin ? CO] _ a>2 A. 2 = 0)2. 3 2 D . CO] -C02- Cau 15. Hai thanh gd va thep cd kich thudc nhu nhau dupc ghep vdi nhau nhu hinh ve Gpi mdmen quan tinh dd'i vdi true A trong trudng hop a la 7^, trong trudng hpp b) la 7^. Nhan xet nao diing ? A. 7« > 7^. B. 7, < h a) Go Thep b) G6 Th6p 49 C. 1, = It. D. khdng so sanh dupe vi thieu dilu kien. Cau 16. Mdt dTa trdn ddng chat cd khd'i lupng m = \kg quay diu vdi tdc dp gdc CO = 6rad / s quanh mdt true vudng gdc vdi dTa va di qua tam cua dTa. Ddng nang cua dTa bing 97. Ban kinh cua dTa la A. R=l,Om. B. R=l,3m . C. R=1.4m. D. R=l,5m . H-BA I TAP TU LUAN Bai 1. Mdt vat rin bit dau quanh nhanh din diu quanh mdt true cd dinh, sau 6s nd quay dupc mdt gdc bing 36 rad. a) Tinh gia tdc gdc ciia banh xe. b) Tinh toa dp gdc va tdc dp gdc ciia banh xe d thdi diem t = 10s tinh tir liic bit dau quay. c) Vilt phuang trinh va ve dd thi bilu diln su phu thudc cua toa dp gdc ciia vat rin theo thdi gian. Bai 2. Cho hai thanh hinh hop chii nhat cd kich thudc hinh hpc nhu nhau, mdt thanh dupc lam tir gd, thanh kia tir thep ; mdi thanh diu ddng chai G6 Thep Ngudi ta ghep chiing lai vdi nhau thanh mdt thanh ; O,, 02 ^i tam ciia mdi thanh. Khd'i tam cua thanh ghep nim P DAFAND^2 I - BAI TAP TRAC NGHIEM 1. Cau hdi nhieu lua chon Cau Cau 50 1 B 9 A 2 C 10 B 3 D 11 A 4 C 12 C 5 B 13 B 6 B 14 C 7 D 15 A 8 D 16 A n-BA I TAP TU LUAN Bai 1. Chpn md'c thdi gian r = 0 tai thdi dilm vat rin bit diu quay, toa dp gdc ban dau cpQ = 0. Chpn chilu duong la chilu quay ciia vat rin. a) Tinh gia tdc gdc 1 2 - Ap dung cdng thirc : cp = cpQ +0)^1 + —yt, trong dd cpQ =0, vi van rbat diu quay nen tdc dp gdc ban dau COQ = 0. 1 2 2cp 2.36 2 Suy ra : cp- — yt 7 = —r- = —— = 2rad / s . t^ 6^ b) Tinh toa dp gdc va tdc dp gdc ciia banh xe d thdi dilm sau khi quay dupc 10s -Tac d cp = -yt'^ =-.2.10^ =\00rad. 2' 2 - Tdc dd gdc dupc xac dinh: co = coQ + yt = 0 + 2.\0 = 20rad/s. c) Phuang trinh bilu diln sir phu thudc ciia toa dd gdc cua vat rin theo 1 2 thdi gian cd dang cp = cpQ+ coQt + — yt Mat khac(PQ=0, COQ=0 va the 2 2 ^^'^^'^^ cau a) ta cd y = 2rad / s suy ra ^ = / - Do thi bilu diln sir phu thudc ciia toa dp gdc cua vat rin theo thdi gian chinh la dd thi cua ham sd cp = t^ do thi ham sd la nira nhinh parabol di qua gdc toa dp nhu hinh ve. Bai 2. Tren doan 0]02 nim ben thanh thep. t(s) Hai thanh gd va thep diu la hlnh hop chir nhat kfch thudc nhu nhau, mdi thanh diu ddng chat nen khd'i tam eiia mdi thanh la giao dilm ciia dudng cheo cac hinh hop. 01 : la khd'i tam cua thanh gd ; 02 la khd'i tam cua thanh thep. 51 Chpn true toa dp la Ox di qua O, va O2. Dat 00]= x thi hoanh dp khd'i tam ciia he thanh ghep la : X,= Y.mjXj _ mjjr + m2.3x _ xim^ + 3m2) Sm,- mj + m2 mj + mj = X 1 + 2m2 mi + m2 X^ = X 1 + 2VP2 ViPl +P2) = X 1 + 2/>2 P1+P2 Oo yfh = 7800)tg/m^ ; p, = SOOkg/m^ nen 2,8A: < A;. < 3jf Do dd X(. nim tren doan 0,02 a^en thanh thep. BiS'u DIS'M D^ 2 I - BAI TAP TRAC NGHIEM 0,25 dilm/cau x 16 cau = :4d l H-BAI TAP TU LUAN Bai 1. (4 diem) Xac dinh gia tri / Xac dinh gia tri cp\a co ,, 2 Viet bieu thiic q> = t Ve dd thi Bai 2. (2 dilm) Xac dinh diing vi trf khd'i tam 0, Im. 1 diem. 1 diem. 1 dilm. I dilm. 0,5 diem -C2 Xac dinh hoanh dp khd'i tam cua thanh thep Xac dinh vi trf XQ 52 I dilm. • 0,5 dilm CHUONG ll. DAO DONG CO BAI6 DAO DONG Drfiu HOA I - MUC Tifiu 1. \ i kien thiic - Hiiu dupc khai niem dao ddng, dao ddng tuan hoan, dao ddng dilu hoa. - Dl xuit dupc phuang phap khao sat li thuyet va phuang phap khao sat thuc nghiem de khao sat dao ddng ciia con lie Id xo. - Thue hien dupc phuang phip khao sat li thuyet dl khao sat dao ddng cua con lie Id xo. - Sau khi GV sir dung phin mIm phan tich video dl khao sat dao ddng cua con lie 16 xo, HS du doan dupe nghiem cua phuang trinh ddng luc hpc ciia dao ddng, kilm nghiem dupc dang nghiem ciia dao ddng ciia du doan. - Nim dupc cac dai lupng dac trung cua dao ddng dilu hoa, chu ki va tin so. - Xac dinh dupc bilu thiic ciia van tdc, gia tdc cua vat dao ddng dilu hoa. Biei each bilu diln dao ddng dilu hoa bing vecto quay. - Biei vi6t dieu kien ban dau tuy theo eich kich thich dao ddng, va tir dilu kien ban dau suy ra bien dp A va pha ban diu cp. 2. Ve ki nSng - Ren luyen cho HS kT nang dua ra cac du doan cd can cii. - Ren luyen kT nang Idgic toan hpc dl khao sat dao ddng cua con lie lo xo. - Ren luyen ki nang thiet ke cae phuang an thi nghiem. - Ren luyen ki nang bilu diln dao ddng dilu hoa bang vecto quay. II-CHUXNBI Giao viin - Chuin bi may chie'u projector, miy vi tinh, phin mem phan tich Video ciia tie gia Nguyin Xuan Thanh - DHSP Ha Ndi. - Chuan bi con lie don, ddng ho bim giay dl do chu ki cua eon lie don. - Phie'u hpc tap cho HS. 53 Hpc sinh - On lai vl dao ham, each tinh dao ham, y nghTa vat li cua dao ham. Ill - THlfiT Kfi' HOAT DON G DAY HOC Hoat dgng cua hgc sinh Hoat dong 1 Kiem tra, chuan bj dieu kien xuat phat. Dat van de HS suy nghT ea nhan tim cau tra loi. HS nhan thiic dupc van dl ciia bai hpc Hoat dgng 2 Tim hieu khai niem dao dgng, dao ddng tuan hoan HS thao luan chung toan Idp. - Cae chuyin ddng tren gidng nhau d chd : vat chi chuyin ddng trong mdt viing khdng gian hep, chuyin ddng qua lai quanh mdt vi tri can bing. HS tie'p thu, ghi nhd. 54 Trg giiip cua giao viSn GV neu eau hdi kiem tra kie'n thiic cu: - Viei bilu thiic ciia luc dan hdi. - Viet phuang trinh dinh luat II Niu- tan. Dgt vdn de : Hang ngay chiing ta thay rat nhilu chuyin ddng khac vdi eac chuyin ddng ma chiing ta da hpc nhu : chuyin ddng cua chiec la cay khi cd gid, chuyin ddng ciia qua lie ddng hd, chuyin ddng cua xich du, chuyin ddng ciia con lie Id xo tren dem khdng khi... Cac chuyin ddng dd cd tuan theo quy luat nao khdng ? Bai hpc ngay hdm nay giiip chiing ta tra Idi cau hdi dd. GV cho HS quan sat chuyin ddng cua con lie don, con lie Id xo tren dem khi tren man hinh may chie'u projector. Sau dd tra loi cau hdi : cac chuyin ddng tren cd dilm nao gidng nhau ? GV thdng bio: - Nhihig chuyin ddng nhu tren gpi la dao ddng. - Dao ddng la chuyin ddng qua lai quanh mdt vi trf can bing. Hoat dgng cua hgc sinh HS suy nghT ea nhan. HS quan sat va riit du doan: - Dd'i vdi dao ddng cua con lie vat ; li va dao ddng cua eon lie Id xo • tren dem khdng khi cd tuan theo [ mot quy luat : sau nhiing khoang • thdi gian nhai dinh con lie lai trd ve vj tri ban diu. ; HS thao luan chung toan lap. - Diing ddng hd bam giay dl do • khoang thdi gian ma mdi lan con j lie vat li trd vl vi tri ban dau. i Dai dien cho ca Idp, hai HS len | tien hanh thi nghiem. Kit luan : Du doan tren la diing. ; HS tie'p thu, ghi nhd. Trg giiip cua giao vien GV neu cau hdi dl HS tim hiiu dao ddng tuan hoan: - Cac dao ddng tren cd tuan theo quy luat nao khdng? GV neu cau hdi thiet ke phuang an thi nghiem kilm tra du doan : - Lam the nao dl kilm tra dilu du doan tren? GV thdng nhai phuang an thi nghiem va cho HS tien hanh thi nghiem va rut ra kei luan. GV thdng bao: - Dao ddng chiing ta vira xet d tren la dao ddng tuin hoan. - Dao ddng tuin hoan la dao ddng ma trang thai chuyin ddng ciia vat dupc lap lai nhu cu sau nhung khoang thdi gian bing nhau. - Giai doan nhd nhai dupc lap lai trong dao ddng tuan hoan dupe gpi la dao ddng toan phan hay mdt chu trinh. - Thdi gian thuc hien mdt dao ddng toan phan gpi la chu ki (ki hieu la T) ciia dao ddng tuan hoan. Don vi ciia T la giay is). - Trong 1 giay chuyen ddng thuc hien dupe / dao ddng toan phin, / gpi la tan sd cua dao ddng tuin hoan. f = — dan vi la hec (77z). 55 Hoat dgng cua hgc sinh Trg giiip cua giao vien Hoat dong 3 Nghien ciiru dao ddng ciia vat dao ddng trong con lac 16 xo HS thao luan chung toan Idp. Vi HS da dupe sir dung phan mIm phan tich video d Idp 10 nen cd thi dl xuai cac phuang phap nhu sau : - De nghien ciiu chuyin ddng cua mdt vat bing li thuyet thi chiing ta cd thi van dung dinh luat 2 Niu-ton. - Thi nghiem cin phai xic dinh dupc tpa dp cua vat d mdi thdi dilm va cd thi sir dung phan mIm phan tich video. O OMMMMJlL. F\ <--> f Chpn true toa dp nhu hinh ve, gdc toa dp O tai vi tri can bing. Ap dung dinh luat II Niu-ton ta cd : F = - kx = ma => -kx = mx" => x"+ — x = 0 m Dat a>^ ~^x"+o)^x = Oi*) m 56 GV neu cau hdi vl va'n dl cin nghien ciiu: - Dl tim hiiu quy luat chuyin ddng chiing ta ed the sit dung phuang phap ly thuyet nao ? Ne'u khao sat dao ddng bing con dudng thuc nghiem thi phai tiln hanh thi nghiem nhu the nao ? GV neu cac cau hdi gpi y: - Phan tich cae luc tac dung vao vat. - Viet phuang trinh dinh luat II Niu- tan. Hoat d6ng cua hgc sinh Trg giiip cua giao vien GV thdng bao: - Day la phuang trinh ma eac em chua biet phuang phap giai. Dl du doan nghiem eac em cd thi sir dung phin mIm phan tich video tim hiiu su phu thudc ciia x va t, sau dd thir lai vdi phuang trinh tren. HS thao luan chung toan Idp. - Can cii vao kei qua thuc nghiem ta cd the du doan nghidm cua phuang trinh dupe bilu diln dudi dang ham so sin hoac cosin theo thdi gian. - GV sir dung phan mIm phan tich video dl ve dd thi bilu didn su phu thudc cua X va t va yeu ciu HS du doan nghiem ciia phuong trinh (*). 1- |«i.. -J 1 r fMvB iMiiM 1 ii«- - •• a • .^L& ' \ - 4 • / •«,"»'ji.»Ui» . ,', HS chii y ling nghe. GV thdng bao: - Toa dp X trong phuang trinh tren gpi la li dp. - Nghiem toin hpc cua phuang trinh (*) cd dang : x = ^cos(ft)/+ ^),trong dd A ya q> la hai hing sd bit ki. 57 Hoat dgng cua hgc sinh HS thao luan chung toan Idp. Tim X ", thay x va x" vao phuang trinh (*) dl kilm tra. X' = -co A sini^cot + cp^ x'' = -co Aco^(o}t + cp^ = -co X Thay vao (*) ta dupc nghiem diing. HS tie'p thu, ghi nhd. Hoat dong 4 Tim hieu cac dai lugng dac trung cua dao dgng dieu hoa HS lam viec ca nhan. Bien dp A la gia tri cue dai ciia li dp X \tn% vdi cos(ri>r + cp) = \. Bien dp ludn duong. [cot + cp^ gpi la pha cua dao ddng tai thdi dilm t. Vdi mdt bien dd da cho thi pha xac dinh li dd x cua dao ddng. cp la pha ban dau, tiic la pha {cot + (p) vao thdi dilm t = 0. . 0) gpi la tin so gdc cua dao ddng. 58 Trg giiip cua giao vien GV neu cau hdi dl HS kilm tra sU diing din ciia nghiem cua phuong trinh: - Dl khing dinh x = Acos{cot+ (p)la nghiem cua phuong trinh (*) ta phai lam the nao ? GV thdng bao: - Phuang trinh x = A cos {cot + cp) cho su phu thudc cua li dp x vao thdi gian , gpi la phuang trinh dao ddng. - Dao ddng ma phuang trinh cd dang la ham cdsin hay sin cua thdi gian nhan vdi mdt hing so, gpi la dao ddng dilu hoa. GV yeu ciu HS dpc SGK va cho biei y nghTa cac dai lupng dac trung ciia dao ddng dilu hoa. Hoat ddng cua hgc sinh HS lam viec ca nhan. j Ta cd : • 4.7r x = -5cos(;rr ) i 3 ; 4.;r = 5eos(;rr \-n:) | => X = 5 cos(;Tr )icm) ; Suy ra cac dai lupng dac trung cho ; phuang trinh la: Bien dp dao ddng : A = 5cm. '• TT ' Pha ban diu : cp = • 3 ; 7C '< Pha dao ddng : (;7-r ). | Tin sd gdc ; co = n rad/s. \ Hoat dgng 5 Ve do thj ciia dao dgng dieu hoa. ; Tur dd, xac dinh bieu thiirc chu ki, ; bieu thiirc tan so' cua dao ddng ; dieu hoa HS lam viec ea nhan. - HS lap bang bie'n thien cua x | theo t va ve dupc dd thi ham sd: ; Trg giiip cua giao vien GV yeu ciu HS chi ra cac dai lupng dac trung cua hai phuong trinh dao ddng sau : TT X = 3 eos(;r/ H—)(cm) 4 4.;r X = -5 eos(;T/ )icm) HS se gap khd khan trong qua trinh chi ra cac dai lupng dac trung cua phuang trinh vdi phuong trinh dao ddng 2. GV neu cac cau hdi gpi y. - Bien dp dao ddng ludn cd gia tri nhu the nao ? - Dl bieri dp dao ddng ludn duang ta cin phai bie'n ddi phuong trinh nhu the nao ? - Mud'n dua dau tru vao ben trong bilu thiic ta cin phai ap dung tinh chat lupng giac nao ? GV yeu ciu HS ve dd thi ciia dao ddng dilu hoa. Tu dd, xac dinh bilu thiifc chu ki, bilu thiic tin so ciia dao ddng dilu hoa. Cho biet dao ddng dilu hoa ed phai la dao ddng tuin hoan khdng ? Tai sao ? 59 A 0 Hoat dgng cua hgc sinh \ 111 1 \ / ' \ Trg giiip cua giao vien -A \ ' / \ ' / \ ' / . r \ / ' \ / >* >y T ' ; Tir dd thi li dp cua dao ddng dilu • hoa ta tha'y: : - Dao ddng dieu hoa la dao ddng • tuin hoan. • - Giai doan chuyin ddng tu thdi ; 27r 1 diem t = 0 den t = — la giai doan ; CO I ngin nhai dupc lap lai lien tuc va ; mai mai, dd la mdt dao ddng toan ; phan. Suy ra chu ki T ciia dao ddng ; dilu hoa \a: T = • CO \ - Tin sd cua dao ddng dilu hoa • 2TT \ Hoat dgng 6 Xac djnh van tdc va gia tdc cua \ dao ddng dieu hoa HS lam viec ca nhan. • - T a cd : v = x' = -(y^sin(dyr + ^ ) ; = CO A cos f ^ 1 cot + cp-\— I 2 j a = x" = v'= -co Acos{^cot + cp) \ = -co Acos{cot + q)) \ 60 GV yeu ciu HS xac dinh van tdc va gia tdc cua vat dao ddng dieu hoa, riit ra nhan xet vl su bie'n ddi ciia van tdc va gia tdc theo thdi gian. Hoat ddng cua hgc sinh - Van tdc va gia tdc ciing bie'n thien dilu hoa cung tan sd vdi li dp x. - Van tdc cd gii tri cue dai v = coA khi li dp X = 0, va cd gia tri cue tilu V = 0 khi li dp x = ±A. - Gia tdc ngupc pha vdi li dp x. Hoat dgng 7 Tim hieu each bieu diln dao dgng dieu hoa bdng vecto quay HS lam viec ca nhan. I ^ 1 "^ - Vao thdi dilm t, gdc giua true Ox va vecto OM la [cot + '(0) = 0 \ \ Thay vao phuang trinh ; : Trg giiip cua giao vien - Phuang trinh dao ddng dilu hoa cua con lie ed dang nhu the nao ? x = yl cos((y/+ ^) , ta dupe : ; ; x(0) = ACOS[(P) = XQ ; ; - Cdng thiic van tdc ciia vat dao ddng dilu hoa ? - Cin phai xac dinh nhiing dai lupng nao trong phuang trinh ? viO) =-coA sin cp = 0 ': ; Giai he phuong trinh : |^eos{c?) = Xn IA = XQ ; ^^^ " ta duoc : : [-ft;^sin^ = 0 [^ = 0 Vay phuang trinh dao ddng dilu : hoaeiiaconlie la : x = xoeos{ -pgsz = mz" ,„, Pffl,_ r' + 0 m 2 PgS =>z"+co^z=0. D a t CO- = m Vay, phii ke dao ddng 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 dd thao luan chung toan Idp. a) Theo dau bai ta cd : . , . TT 5TT =>/ = 5;r TT\ 1 1 = — s \OTT 30 Vao thdi dilm / = — s thi pha dao 30 STT ddng bang — , khi dd : 6 ^ , 57r - , ^ X = z, 5 cos — = -2,16cm. 6 b) Theo dau bai : x = 2,5cosO = l,25 cos 0 = 0,5 TT ^ = ±- + 2kTT, 3 GV yeu ciu HS tie'p 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 ddng da cho la pha dao ddng ? - Pha ciia dao ddng nhan gia trj nao khi x= 1,25cm ? 81