TIM HIEU KIEN THlTC CAC LUC HU''''dNG TAM, LY TAM VA QUAN TiNH LY TAM DAO PHU QUYEN Trircmg DHSP Ha Noi I Md dau Trong cac bai bao gan day tdi cd trinh bay tac dung cua lire quan tinh ly tam tdi su det d[.]
TIM HIEU KIEN THlTC CAC LUC HU'dNG TAM, LY TAM VA QUAN TiNH LY TAM DAO PHU QUYEN Trircmg DHSP Ha Noi I Md dau Trong cac bai bao gan day tdi cd trinh bay tac dung cua lire quan tinh ly tam tdi su det d hai cue eua Trai Oat, su hinh he Mat Trdi, cac hanh tinh, ve tinh De phan biet lire quan tfnh ly tam vdi lire ly tam bai viet tdi xin trinh bay ve cac lire hudng tam, ly tam va quan tinh ly tam II Lire hi/dng tam va life ly tam Khi hpe vat ly phd thdng ta da biet tdi cac djnh luat co hpc cua Niutdn Trong dd djnh luat thir nhat (cdn gpi la djnh luat quan tinh) cua NiutPn ndi rang: Mgi vat se tiep tue giu' nguyen trang thai dirng yen hay chuyen dgng thang deu chirng nao nd edn chua bi vat khac tac dung lam cho thay doi Khi dumg yen hay chuyen dpng thing deu van tdc cua vat ludn khdng ddi Bdi tac dung cua lire vat khac dat len vat ma su difng yen hay chuyen dpng thing deu cua vat mdi bi pha vd Djnh luat thur ba cua Niutdn phat bieu: Hai lue cua hai vat tac dung len co Idn bang va ed hudng nguae Neu gpi F, la lire vat thir nhat tac dung len vat thir hai va F2 la lire vat thif hai dat len vat thir nha't thi bieu thirc cija djnh luat thif ba ciia Niuton la: Fi = -F2 Vdi F^itFjVa |FJ = |F2| Neu F, gpi la luc thi Fj gpi la phan lire Djnh luat thir ba cua Niuton neu len sir tac dung tuong ho cua cac vat Nd khing dinh rang tu nhien sir tac dung cua cac vat khdng xay theo mpt chieu ma ludn cd tfnh chat hai chieu; ca hai vat ludn tac dung len ddng thdi va cac luc tuong tac (lire va phan luc) la nhtfng luc true ddi Chu y rang lire va phan lire cd dp Idn nhu va cd hudng ngupc nhung chung la hai luc true dd'i chir khdng phai la hai luc can bang vi chung cd diem dat len hai vat khac (xem hinh 1) F, < ^ • •- (1) (2) • F, - (1) Vat (1) va vat (2) day F, - (2) Vat (1) va vat (2) hut Hinh Hai life triTc doi Hai lire can bang la hai lire ngupc hudng, cd dp Idn nhu va cung dat len mpt diem d mdt vat (xem hinh 2) 54 '"^MG i n i m u i gKB^B TIM HIEU KIEN THLTC A -©Hinh Hai li/c can bang Trong hinh hai lire can bang F, va Fj eimg dat len mpt diem tren vat A, hop lire eua hai luc F = F, + Fj = Neu lue dau vat A dimg yen thi hpp lire F = tac dung len nd khdng gay eho nd mpt gia tdc nao, vat A vin tiep tue dumg yen d vj trf can bang Neu vat A ehuyen dpng thi hpp luc F = tac dung len nd cung khdng lam cho van tde eua A bien ddi Trong vat ly phd thdng ta cdn biet rang dieu kien de mdt vat chuyen dpng trdn la cd lire hudng tam tac dung len nd Cay cdi, nha ci^a, da't da sau 24 gid chuyen ddng quay quanh true Trai Dat mpt vdng la cd lire hudng tam tac dung len ehiing Lire hudng tam la phan hudng vao true quay cua Trai Oat cua lire hap dan cija Trai Dat dat len vat (xem hinh 3) Hinh V Lire hudng tam cd dp Idn la F„= mco^p hay F^, = m — , vdi m la khoi lupng cua vat bj tae dung, CO la vin tdc gdc, v la van td'c dai va p la ban kfnh quy dao Luc hap din cua Trai Dat tac dung len Mat Trang la luc hudng tam lam cho Mat Trang chuyin dpng tren quy dao trdn quanh Trai Dat (xem hinh 4) Mj, Mat Trang Hinh 55 TIM HIEU KIEN THlTC Theo dinh luat thir ba cua Niuton va djnh luat van vat hap din (cung cua Niuton) Trai Dat tac dung len Mat Trang luc hap din F^, thi Mat Trang cung tac dung lai Trai Oat mpt phan lire F|, Luc dat tai tam Trai Oat va hudng xa tam quy dao cua Mat Trang n§n dupc gpi la lire ly tam Ff,, va F,, la hai lire true dd'i, dat len hai vat khac nhau, cimg phuong, ngupc chieu, cd gia tri MJVI, bang va deu bang: F = k-f^—vdi k la hang sd hap dan, Mj- la khdi lupng Trai Oat, M, la R khdi lupng Mat Trang va R la ban kfnh quy dao cua Mat Trang Tuong tu nhu tren, eac hanh tinh chuyen dpng quanh Mat Trdi la cd luc hudng tam la luc ha'p din ciia Mat Trdi tac dung len chung Cac ve tinh quay quanh hanh tinh la cd lire hudng tam la lire ha'p din ciia hanh tinh len ve tinh; cac phan iii cua khdi khf bui ban dau tao he Mat Trdi chuyen dpng quanh true khdi la lire hap dan cua khdi khf bui tac dung len chiing Mdi phan tir chuyen dpng tren quy dao trdn cung tac dung lai vat tac dung len nd lire hudng tam mpt luc ly tam Lire ly tam khdng tac dung len phan tur chuyen dpng trdn nen khdng lam phan tir ehuyen dpng trdn di xa true quay de lam cho vat quay bj det lai Bdi vay ndi lire ly tam lam cho vat quay bj det lai d hai cue la khdng dung III Life quan tinh ly tam Trang thai chuyen ddng cua vat dupc bao toan (tifc van td'c chuyen dpng cua vat ludn khdng ddi) chi khdng ed vat nao tac dung len vat hoac hpp lire cua cac vat tac dung I6n nd bang khdng Vdi vat chuyen dpng trdn deu, cd ngudi hdi rang: theo phudng ban kfnh luc hudng tam cd gia trj khae khdng se gay cho vat mpt gia tdc lam vat phai chuyen dpng nhanh dan deu ve phia tam quy dao nhung hien tupng khdng xay va vat van tiep tue chuyen dpng trdn deu tren quy dao la tai sao? Cd giao vien khdng giai dap dupe cau hdi nay, hp chi tra Idi cho ngudi hdi la theo ly thuyet thi lire hudng tam khdng gay cho vat gia tdc, chi lam bie'n ddi hudng van tdc chuyen dpng cua vat Oe tra Idi cau hdi tren ta phai chu y la ddi vdi vat chuyen dpng trdn thi ngoai luc hudng tam cdn cd luc quan tinh ly tam tac dung len vat Khi vat chuyen dpng trdn deu vdi van tdc gdc CO, theo phuong ban kfnh, luc hudng tam va lire quan tinh ly tam tac dung len vat la hai lire can bang Hai luc cung tac dung len vat, cd cung phuang, ngupc chieu va cd dp Idn nhu nhau: F^, = -mco^R F„„ = mco^R Hpp luc cua hai lire bang khdng Theo phuong ban kinh vat ludn d vi trf can bang nen nd mdi chuyen dpng trdn deu tren quy dao 56 Til [; lK"f:&: XDHjCa TIM HIEU KIEN THUC Trong Phuang trinh ddng luc hgc cua chuyen dgng tuang doi d trang 46 Ban tin Giao due Tirxa va Tai ehirc sd (thang 1/2006), chiing tdi cd de cap tdi lire quan tinh ly tam vdi bieu thifc: F^,,, = -mo3x(coxR) Ban dpc cd the dpc lai de tham khao Luc ly t&m va lire quan tfnh ly tam la hai lire hoan toan khae (xem hinh 5): Hinh Life ly tam, liTc hi/dng tam va life quan tinh ly tam Ve diem dat: Luc quan tinh ly tam dat len vat ehuyen dpng trdn, edn lire ly tam khdng dat len vat chuyen dpng trdn - Ve phan lire: Luc ly tam ed phan lire la lire hudng tam edn lire quan tfnh ly tam khdng cd phan lire Luc ly tam va lire hudng tam thude loai lire tuong tae, edn lire quan tinh ly tam ndi rieng cung nhu cac lire quan tfnh ndi chung khdng phai la loai lire tuong tac Khi mpt vat chuyen ddng thing deu, neu khdng bj vat nao tac dung nd se ludn ehuyen dpng thing deu, van td'c chuyen dpng cua vat ludn khdng ddi ve phuong, chieu, dp Idn Neu vat dd bj vat khac tac dung mpt lire cd phUdng khae phuang ehuyen dpng eua vat thi quy dao cua vat se bi eong di va neu phuong tac dung cua lire vudng gdc vdi phudng chuyen dpng cua vat cd the lam cho vat phai chuyen ddng trdn Do quan tinh ma vat cd xu hudng bao toan hudng van tde chuyen dpng, turc ludn ed xu hudng rdi xa tam quay cua quy dao Day chfnh la ngudn gdc eua lire quan tfnh ly tam Luc quan tfnh cd ngudn gd'c tir quan tfnh cua vat chif khdng phai lire vat khac dat len vat dd cac lue quan tinh khdng thupe loai lire tuong tac va chiing khdng cd phan lire IV Ldi cuoi bai Nam dupc chac khai niem cac lire hudng tam, ly tam va quan tinh ly tam, giao vien se giang day tdt han va van dung giai thich dupe nhieu hien tupng tu nhien nhu su udn khue cua ddng chay, sir tao cac dja hinh ven ddng chay, sdng ben Id ben bdi, su det cua Trai Oat d hai cue, sir hinh he Mat Trdi va cac hanh tinh, ve tinh 57 ... lire quan tinh ly tam vdi bieu thifc: F^,,, = -mo3x(coxR) Ban dpc cd the dpc lai de tham khao Luc ly t&m va lire quan tfnh ly tam la hai lire hoan toan khae (xem hinh 5): Hinh Life ly tam, liTc... hi/dng tam va life quan tinh ly tam Ve diem dat: Luc quan tinh ly tam dat len vat ehuyen dpng trdn, edn lire ly tam khdng dat len vat chuyen dpng trdn - Ve phan lire: Luc ly tam ed phan lire la lire... tam mpt luc ly tam Lire ly tam khdng tac dung len phan tur chuyen dpng trdn nen khdng lam phan tir ehuyen dpng trdn di xa true quay de lam cho vat quay bj det lai Bdi vay ndi lire ly tam lam cho