DisniwjHpc 807 201 JNGAY NAY 1 w 51 Nang cao chat liTdhg day hoc cac dinh luat bao toan nang lifgmg Vat li 10 THPT PGS TS NGUYEN DINH THl/CfC Trudng Dai hpc Vinh ThS NGUYfiN VAN PHlfdNG Sd GD & DT Ngh[.]
DisniwjHpc 807-201 w JNGAY NAY _ _ _ _ 51 Nang cao chat liTdhg day hoc cac dinh luat bao toan nang lifgmg- Vat li 10 THPT PGS.TS NGUYEN DINH THl/CfC Trudng Dai hpc Vinh ThS NGUYfiN VAN PHlfdNG Sd GD & DT Ngh§ An y nghTa, tam quan trpng cua cac djnh lu^t bdo loan chUdng trinh V^t ly phd thdng Cde djnh ludt bao todn cd vai trd ddc bidt quan trpng vdt \)i hpc, dd Id nhQng djnh ludt tdng qudt, dp dyng cho mpi hd kin, td vi md den vTmd; Trong the gidi vi md, cde hat chuyen ddng gan vdi tdc dd anh sdng, eP hpc Niu-tOn khdng ddng nda, thay the b I n g cP hpc tuPng ddi tfnh eda Anh-xtanh; dd cdng thdc ddng lupng cd d^ng tUdng ddi tfnh nhung djnh lu^t bao toan dpng luting v3n ddng eho mpi trudng hpp cac h^t vi md tUdng tae vdi nhu qua trinh va cham, phan hodc phan dng hat nhdn Ngodi djnh ludt bao todn ndng lupng cdn dp dyng cho tat ca cac hi^n tupng eda the gidi vd sinh va hOu sinh Cac djnh ludt bao todn tdng qudt hdn cde djnh ludt Niutdn vl chung g i n lien vdi tfnh chat cua khdng thdi gian Djnh ludt bao toan ddng lupng phdn anh tinh chat ddng tfnh cua khdng gian; Djnh 1u$t bdo toan nang lupng phan dnh tfnh chat ddng nhat cua thdi gian Cde djnh ludt bao todn cd y nghIa Idn ve mat phUdng phdp ludn (phUdng phdp bao todn hay quan diem bdo todn, tu tudng bao todn ddng de nghien cdu Vdt 1^ hpc); PhUdng phap bao todn Id phUdng phdp sd dyng cde djnh ludt bao todn nhu nhOng phUdng trinh cd bdn gidi bdi todn vdt ly; nd khdng ch? bd sung cho phUdng phdp ddng lUc hpc ma cdn thay the hodn todn trUdng hdP khdng dp dyng dupe phUdng phap ddng li/c hpc khdng biet rd cde luc tdc dyng (nhu trUdng hdP va cham, no )Cde djnh ludt bao todn la cdng cy de tim kiem cde gia thuyet nghien cdu hodc ki^m tra sU dung dan cua cde gia thuyet; n^u d dau xua't hien su vi pham dinh ludt bdo todn thi d dd da xuat hi^n sy vdt, hi#n tupng vdt ly mdi, ddy la mdt cac cd sd eda nhOng phdt minh v l vdt ly Trong Co hpc Idp 10 THPT, hpc sinh dupe nghien cdu hai djnh l u | t bdo todn: bdo todn ddng lupng vd bao todn cd nang (ta trudng hpp rieng cua djnh ludt bao todn nang lupng) Tu tudng bao todn, phUdng phdp bao todn dupe qudn tridt todn bd chUdng trinh Vat ly phd ttiong; Nhieu djnh ludt Vdt ty dUpe trinh bay nhU Id he qua suy ludn ty thuyet td dinh ludt bdo todn: djnh ludt Bec-nu-ti, dinh ludt Ohm todn mach, ede nguyen ly nhldt ddng lye hpc, ; cac djnh ludt bdo todn Id cd sd vdt ly cua nhieu dng dyng k^ thudt quan trpng: chuyen ddng phdn tyc, cdng nghiep nang lupng, hodn thien cde thiet bj ky thudt Vi the, day hpe cac djnh ludt bao todn cd nhieu thudn Ipi de bdi dudng phUdng phap nhdn thdc vdt 1;^, giao dgc the gidi quan khoa hpc vd gido dye k9 thudt tdng hpp cho hpc sinh, gdp phdn thUe hidn ddng thdi nhiem vy eua day hpc vat ly, khdng ch7 ddn t h u i n nhidm vu gido dudng nhu quan niem kha phd bien hidn thtfc t i l n day hoe ThUc trang d^y hpc cac djnh lu#t bdo toan d ldp 10 trUdng THPT Trong chUdng trinh Vdt ly THC8, hpc sinh da dUpc nghien cdu d mdc dp djnh tfnh cde khdi niem ve cd nang, the nang, ddng nang, nang lUdng, dinh tuat bao todn edng, djnh ludt bao toan ed nang, dinh ludt bao todn vd chuyen hda nang lupng d Vdt ly 10, nhOng kien thUe dd dupe nghien cdu sau hdn vd d mdc dp djnh lUdng; ngodi djnh ludt bao todn ddng lUpng dupe nghien cufu trpn v^n Cdu trdc logic tdng npi dung phu hpp vdi trinh dp nhdn thdc cua hpc sinh, tUdng dUdng sdeh gido khoa cua ede nude cd nen gido dye phdt trien nhU CH Phdp, CHLB Ddc, CHLB Nga, Trong cde trudng phd thdng, thiet bj thf nghiem chf ed the kiem chdng djnh ludt bao toan dpng tupng; vipe kiem tra b l n g thye nghiem djnh ludt bao todn eP ndng, djnh ludt bao todn nang lupng chua thue hi^n dupe md ehi md phdng bIng ede thf nghifm Qua dieu tra khao sdt di$n hpp d mdt sd trudng TtHPT d Ngh# An, da ed mdt sd nhdn djnh sd bd: 52 Ve nhan thuc: Da s6 giao vien thupc dien khao sat da nhan thuc duoc vi tri tam quan trong, chuc nang phuomg phap luan va chuc nang giao due the gidi quan cua cac dinh luSt bao toan chuang trinh vat ly thong; song day hoc nang ve nhiem vu trang bi kiSn thuc (nhiem vu giao du6ng), tham chi tuyet doi hoa nhiem vu nay; mat khac thuc hien nhiem vu giao du6ng thi mat dinh tinh, y nghTa vat ly cua cac khai nifm ca ban phdn thudng bi xem nhe, chi chu y mat djnh lugng; nhieu giao vien khong xac djnh dugc mat dinh tinh (y nghTa vat ly) cua cac khai jniem: dong luang, cong,, nang lugng; khong giai thich.dugc vi dgng lugng va nang lugng cua he co lap lai dugc bao toan; thuc te nhan thurc ciia giao vien din ^8n thuc trang day mang tinh hinh thurc, hoc sinh thuoc long djnh nghTa khai niem, phat bieu dugc djnh luat, tham chi ap dung dinh luat giai dugc cac bai tap giao khoa mang tinh luyen tap, nhung khong nam dugc ban chat vat ly; ket qua kiem tra, thi dat diem cao sur dung hinh thiic trac nghiem khach quan, noi dung de thi nang ve tai hien djnh lugng cang khuySn khich tinh trang day hoc Ve phudng phap giang day: Sur dung bien day hoc thong baO va giang giai - minh hga, chua phat huy dugc tinh tich cue, chu ddng va sang tao cua hpc siiih De xuat bien phap nham nang cao chat lugng day hge cac dinh luat bao toan ff THPT 3.1 Giao vien cSn nhSn thdrc chinh xac dSy du noi dung cua kiSn thiic cin day bao gdm cac khai niem: dgng lugng, naiig lugng, cong, cong suat, dong nang, thi nang, ca nang va cac dinh luat: bao toan dpng lugng, bao toan ca nang, bao toan ndng lugng Nam vung va sau sac noi dung day hoc la dieu kien cin de nang cao chat lugng day hoc NhOng khai niem neu tren thoat nghe la quen thuoc vai giao vien vat ly, song hieu day du chinh xac noi ham cua chung chi la mdt ty le thip; day la nhttng khai niem khd dac biet la khai niem cong va ndng lugng; ljch sii vat ly hoc da mat hang tram nam cho viec xay dung nhOng khai niem Cac khai niem CO ban chuang "cac djnh luat bao toan" deu la cac dai lugng vat ly; theo each phan loai khai niem 16-gic hoc, dai lugng vat ly thuoc nhdm khai niem djnh lugng, vi th6 noi ham khai niem vira co diu hieu djnh tinh vira co dau hieu djnh lugng; nhien thuc te cho thay hau nhu giao vien khong chu y den diu hieu djnh tinh cua cac khai niem nay, danh mit y nghTa vat ly cua khai niem la mot thieu sdt Idn cin khac phuc Sau day la noi dung chfnh cua cac dan vj kien thiic neu tr8n can phai dugc hoc sinh ITnh hoi: •,»?&g i 807 2011 _ _ _ _ _ _ DguvdHpc JNGAY SAY Dgng lugng cua mot vat la dai lugng vat ly dac trung cho khd ndng truyen chuyen ddng cua nd cho mot vdt khde, dugc bdng bilu thuc p = mv; d6ng lugng co tinh tuang doi, phu thuoc he quy chilu; CO tinh cong dugc (dgng lugng cua he mot he quy chilu nao bdng tong vec ta dgng lugng cua tCmg vat he doi vdi he quy chilu do; vifc khong thdng nhit he quy chilu tinh tdng dgng lugng cua he la sai lam kha biln can dugc chu y dl khde phuc); Dgng lugng tdng cong cua he co lap dugc bao toan - Nang lugng cua vdt la dai lugng dac trung cho khd ndng Idm bien ddi trgng thdi cua vat hoac cua vat khac tuang tac vai nd; tir dd suy diu hieu nhan biet vat co nang lugng la khd ndng lam thay doi vi tri, van toe (kha nang sinh cong) hodc nhiet (kha nang truyen nhiet); nang lugng ton tai a cac dang: ca nang, nhiet nang (nhan biet dugc true tiep, qua cac diu hieu vT mo neu tren); dien nang, hda nang, quang ndng va nang lugng nghi, cac dang khong nhan bilt true tiep qua cac dau hieu vT mo ma nhan bilt gian tiep qua ca nang va nhiet nang; Nang lugng chuyen hda tir dang sang dang khac, truyen tu vat sang vat khac, nang lugng tong cong cua he co lap dugc bao toan - Cdng Id so luang ndng luang bien doi tir dang ndy sang dgng khde hodc truyen tir vdt sang vdt khde, bieu thiic A = FScosa (ap dung cho lire khong doi va djch chuyen thang); Cong va nang lugng CO moi lien he: bien thjen ca nang cua vat mot qua trinh bang cong cua ngoai lire (tru luc the) thuc hien trorig qua trinh (djnh luat bao toan nang lugng); neu vat chi chju tac dung cua luc ,the thi ca nang bao toan (djnh luat bao toan ca nang) 3.2 Bo sung vao noi dung day hge diu hieu djnh tinh cua cac dai lugng vat ly phu hgp trat tu hinh cde dan vj kiln thuc, dam bao tinh 16-gic va phii hgp vdi nang lire nhan thurc cua hge sinh Ve ca ban, 16-gic phat trien maCh kiln thiic chuang theo sach giao khoa la phu hgp; nhien nhu da phan tich 3.1 can bo sung y nghTa vat ly cua cac dai lugng vat ly quan trgng - Khai niem dgng lugng: Sau thong bao khai niem xung lugng cua luc, suy luan logic tir djnh luat II Niuton cho truang hgp vat khoi lugng m, dang chuyen dgng vai van t6c v, chiu tac dyng lire F khoang thai gian At dat din v$n t6c v^ da di din bieu thiic 'WV2 - mv^ = FAt; Din ddy khai niem dgng lugng dugc djnh nghTa theo budc: J t o / ^ a y s o 7-2011 + Buac DIU hieu djnh lugng ciia khai niem dgng lugng dugc xde djnh bdng thong bao, dat ten: dai lugng bdng tich_kh6i lugng vd vdn t6c ggi la dgng lugng (thuc tiln day hge da s6 giao vien kit thiic viec djnh nghTa dgng lugng a budc 1) + Budc Phan tich ban chit vat ly (diu hieu djnh tinh cua khai niem): mv tinh chit gi cua vat? dd la cdu hdi dat vin dl; GV neu vi du trd chai biing bi, bi-a so saiih va cham cua cde bi cung khii lugng nhung v|n t6c khac vdi cung mpt vien bi dumg yen, kit qua bi nao cd van t6c 1dm han se truyin cho bi diing yen van tie Idn han; sau HS tu so sanh ve va cham cua cac bi cung van tdc nhung khii lugng khac vdi mot bi dung yen, dl neu dugc nhan xet vat cd kh6i lugng cang Idn cang cd kha nang truyin cho vat khac van toe Idn Dgng lugng vira ty le vdi van tdc vira ty le vdi khdi lugng ddc trung cho Vat khd ndng truyin chuyin ddng cua no cho vat khde =»^lS= 53 vung phat triln gin cua Vygotsky; dac dilm dl nhdn thay cua day hge giai quylt vin dl la: xay dvmg tinh hudng cd vin dl dl khdi d6ng tu HS va hudng din HS tirng budc giai quylt vin dl phdng theo phuang phap nghien curu cua nha vat ly Ly thuyet ye day hge gidi quylt vin dl (hay day hpe neu vin dl) ddi tu nhung nam 60 cua thi ky 20 song van dung thuc tiln day hpc d nude ta cdn rdt han chi Day la mgt bien phap cdn dugc trinh bay d6e ldp chung t6i se gidi thieu mpt bai bao khde 3.4 Khai thac y nghTa trilt hpc, y nghTa phuang phdp luan cua eae ngi dung day hpc nhdm gdp phdn bdi duang thi gidi quan va phuang phap luan nhan thiic cho hge sinh Cac dinh ludt bao toan cd y nghTa trilt hpc sau sdc nhung hilm dugc khai thac thuc tl day hge mgt phan nhan thiic eua giao vien va mgt phIn han ehi vl quy thdi gian Dl khde Khai niem cong: ngi ham dly dil cua khai phuc, cin nhan thuc dugc y nghTa trilt hpc cua cac niem cdng cung phai dugc xay dung qua giai dmh luat bao toan; - Bao todn dpng lugng la bao todn chuyin ddng, doan; giai doan (neu dugc diu hieu dinh lugng) d bai 24 (C6ng va cong suit) - da s6 giao vien chi chuyin dgng la bit diet - dd la mgt luan dilm triet quan tdm giai doan ndy; giai doan (vach diu hpc vat bien chiing; hieu djnh tinh (tiic la ban chit vdt ly cua khai niem) Bao toan nang lugng la bdo toan van dpng cua day dinh ly dgng ndng Bdng suy luan logic va vdt chat M6i dang nang lugng ung vdi mot dang todn hpc dan gian xdy dung dugc bilu thiic vdn dpng; Thi hien dac tinh kh6ng tu sinh va Cling khong tu mat di cua sy van dpng cua vat chit, 2 ma chi chuyen tu dang van dpng sang dang van —mv^ ffiVj = A; ngoai viec phat biSu •y nghTa dgng khac Sir chuyen hda thdnh lugng duang vat ly ciia bilu thiic - dd la npi dung djnh ly duang tit dang sang dang khac eua nang lugng dpng ndng, giao vien cin phan tich: bilu thuc la bilu hien sir ba.o toan vat chit moi qua trinh khong phai la bieu thurc djnh nghTa cong, ma la bilu cho mpi d6i tugng v6 sinh va hihi sinh thuc neu len y nghTa vat ly cua cong: c6ng la si - Sir van dpng cd quy ludt cua the gidi vat chat, cac sir biln d6i ndng lurgng (a ddy Id sir biln d6i vl lugng - tdng hoac giam vl s6 lugng cung m6t dang quy ludt diu dan gidn Dilu thi hiSn rit ro qua ndng lupng la dgng nang); a cac bai tilp theo se tilp caC dmh luat bdo toan vdi npi dung don gian vd ndng t\ic chi y nghTa vat ly cua cong qua dinh ly thi len quan diem, tu tudng cd gia trj phuang ndng (su tdng/giam vl s6 lugng cung mot dang nang phdp luan dan dudng cho qua trinh nghien ciiu lugng la thi ndng), djnh luat bao toan nang lugng 3.5 Khai thac y nghTa thuc tiln cua ngi dung (sir biln d6i nang lugng tir dang (ca nang) sang day hoc de giao due hpc sinh cd y thiic van dung dang khac (nhiet hang) kien thiic vdo ddi s6ng, gdp phIn giao due ky thuat tdng hgp./ 3.3 Vdn dyng day hge gidi quylt vin dl nhu mdt quan dilm, m6t chiln luge day hoc nhdm kich thich hiing thu nhan thuc cua hge sinh vd b6i duang ndng l\rc tu duy, ndng l\rc giai quylt vin dl, cac Tai lif u tham khao: I.Richard Feynman Tinh chit cac dinh luat vat ly phuang phdp nhan thiic cua vat ly hge Day hge gidi quylt vin de khdng phdi la mgt Nxb Gido due 2003 phuong phap d?iy hge cu thi md la mgt quan diem, Luong Duyen Binh (ehu bien) Vdt ly 10 Nxb Giao due mOt chien luge day hge; cd tac dung Idn vi?e 3.Pham Quy Tu (ehu bien) Vdt ly 10 ndng cao Nxb khde phye tinh chit tai hi?n cua day hge gidng giai Gido due - minh hga dang thjnh hanh hi?n nay; ca sd tam \y Nguyin Diic Tham (ehu bien) Phuang phdp day hge cua d|iy hge gidi quylt vin dl la ly thuylt vl Vdt ly d truang thong Nxb - DHSP hoc tinh huong c6 vin dl cua Rubinstein va ly thuylt ... quan diem, Luong Duyen Binh (ehu bien) Vdt ly 10 Nxb Giao due mOt chien luge day hge; cd tac dung Idn vi?e 3.Pham Quy Tu (ehu bien) Vdt ly 10 ndng cao Nxb khde phye tinh chit tai hi?n cua day... tich cue, chu ddng va sang tao cua hpc siiih De xuat bien phap nham nang cao chat lugng day hge cac dinh luat bao toan ff THPT 3.1 Giao vien cSn nhSn thdrc chinh xac dSy du noi dung cua kiSn thiic... toan ca nang, bao toan ndng lugng Nam vung va sau sac noi dung day hoc la dieu kien cin de nang cao chat lugng day hoc NhOng khai niem neu tren thoat nghe la quen thuoc vai giao vien vat ly, song