NGHIEN CUU & UNG DUNG
NHONG UING DUNG CUA CAC KIEN T H O C VE CHUYEN DONG NEM TRGNG THUC TIEN
ThS. Mai Ngoc Anh Trudng DH Hdng DUrc - Thanh Hod SUMMARY
Throwing motion is a complex motion, the expression of this motion is very diversity in life. The motion of bullet leaving the barrel of a gun. the motion of the missile launcher left and motion of tennis ball leaving the racket face, so on are all throwing motion.
Throwing motion lakes place complex, however the application of the knowledge of the throwing motion is widely applied to life, production and fight. This paper we are pleased to present a summary of the basic knowledge about the throwing motion as welt as their wide applications in every aspect of human life.
Keyword: Chuyen ddng nem, dng dung
Nh^n bdi ngify: 10/5/2014. NgAy duy^ dang: 23/5/2014 I. MO DAU
Chuyin ddng ndm ngang, ngm xign (ggi chung Id chuyin dgng nem) Id hai dgng chuyin ddng phd bien, thudng xay ra trong ddi sdng hdng ngdy. Ddy Id hai dgng chuyin dpng phdc tgp vl nd bj chi phdi bdi nhilu nguygn nhdn khde nhau; nhu lyc hdt ciia Trdi Ddt vd sdc can eiia mdi trudng lgn chuyin dpng cua v^t. Tuy nhign, nlu bd qua sdc can cua mdi trudng vd chi tfnh din lye hdt cua Trdi Dit tdc dyng lgn v^t thi chuyin ddng cua v^t sS dien ra don gian hon nhilu.
Chuyin ddng ndm diln ra rit phdc tgp nhung edc kien thdc lien quan din chuyin dpng lgi ed nhilu ung dyng trong ddi sdng, sdn suit vd trong ehiln ddu.
Dudi ddy chung tdi xin trinh bdy tdm tat nhttng kien thirc CO bdn vl chuygn ddng ngm cung nhu cdc ung dyng rpng rdi ciia ehdng dang diln ra trong ddi sdng hdng ngdy cua con ngudi.
II. NOI DUNG
2.1: Salugc vi chuyin dgng nim.
2.1.1. Chuyen dpng nem xien: De nghien cihi chuyin dong nem xien trong truong hop chi tinh din trpng l\rc tac dyng len vat, nguoi ta thudng su dyng phuang phap tea dp. Theo phuang phdp nay, chuyen dpng ciia vat dupe phan tfch th^nh hai chuyen dpng thanh phan diln ra dong th6i theo hai tryc tpa dp Ox va Oy {cung ndm trong m^t phang nem).
* Chuyin ddng diln ra theo trye Ox Id chuygn dOng thang dlu ed v§n tde, gia tie vd dudng di d thdi dilm t dugc xdc djnh:
v^^ = v^ = V(j COS a = const
a^=0 (1) X = V^J = VnCOSaJ
* Chuygn ddng dien ra theo tryc Oy Id chuygn dgng ehgm din dlu cd vdn tdc, gia tdc, dudng di dugc xdc dinh;
% = V o S i n a ; a ^ = - g
1 , <2) v ^ = V o S i n a - g t ; y = V o , t - - g t Tir (1) vd (2) suy ra quy dgo, dp cao vd tdm xa dgt duge trong chuygn dgng dugc xdc djnh:
-gx
2 v . - 4- (tan a ) x VnSin'a v^ sin 2 a H = ;L =
2g g (3)
2.1.2. Chuyin dgng nem ngang: Mpt vai ditijc nim ngang tir dO cao h so vcti mjl dli, nSu bo qua siic can cua moi trudng vi dung phirong phdp to? dp dfi TAP CHl THlfTBIGlAO DMC-56106-6/2014 • 3}
NGHIEN CUU & U N G D U N G
nghien cilu, Ihi chuyin dong ciJa vit co thg phan tfch thanh hai cliuyin dong thanh phta dgc theo hai true Ox vi Oy nam trong mat thang dthig.
- Chuygn ddng theo phircmg nem fachiiyfindOng thing d6u theo quan tinh. Theo phuofng nay, van t6c, gia t6c va tea dp cua vSt * thdi diim t duoc xSc dinh:
\^x = v . = const; a, = 0
1 (4) lx = v,.t = v,.t
- Chuyen dpng theo phuang Oy la chuyin dflng rai tu do. V§n tic, gia t6c, toa dp v^ quj dao ciia vSt d thdi gian t diroc xae dinh:
% = 0 ; v , = gt g ; y = - g t 1 x^
(5)
2%S
2.2. Mpt sd thi du vi nhitng irng dung cda cdc kiin thue vi chuyin dpng nim.
Thi du 1: Mpt ngudi linh cuu hda dung cdch . tda nhd dang chdy 50m, cam vdi phun nude ehleh mdt gdc a , so vdi phuong ngang. Vdn tdc cua ddng nude luc idi khdi vdi Id 40m/s. Hdi ngudi linh cdn hda cdn phai cam vdi nude eheeh mdt gde bao nhieu so vdi phuong ngang de ddng nude phun tdi dg eao Id 20m cua tda nhd? Ldy g = 9,8m/sl
Luoc gidi:
x = V. c o s a . t = ^
t = 50
v.cosa 40.0,866 1
= 1,443s
y = Vo.sina.t—-gt =>
sina = ^ ^ ^ ^ = - = > a = 30"
2v„t 2
T h i d u 2 : Mpt cSu thu bdng rd ddng cdch xa rd
20m, nem bdng vdo rd d dO eao 2m vdi gdc ngm 45°
so vdi phuong ngang. Mi^ng r6 d dp cao 3,05m so vdi m§t dit (hinh vS). Hdi ngudi iy phdi n6m vdi tic dd bing bao nhidu &k bdng roi vdo trdng rd.
LiTffc gidi:
X 20 x = v c o s a . t = > t = = pr
Vocosa VoV2 y = VQ.sina.t—gt^
(3,05 - 2) = 1,05 = 10 - 4 , 9 ( - ^ ) ' = s > 20 V0V2 V o = 1 0 , 4 5 ( m / s ) » 1 0 m / s
t
2Dm ""^ 3.05m Thi dy 3: MOt mdy bay, bay ngang vdi v§n ticV, d dd cao h mudn tha bom trdng mpt tau ehiln dang chuygn ddng thing dlu vdi vdn tdc v^ trong cung mJt phing thing ddng vdi mdy bay. Hdi mdy bay phdi edt bom khi nd edeh tdu chiln theo phuong ngang m^t dogn / la bao nhieu? Xdt hai trudng hpp:
a). May bay vd tdu ehiln chuyin dOng cdng chieu.
b). Mdy bay vd tdu chiln chuyin ddng ngupc chieu.
LiTQ-c gidi:
a). Trudng hgp mdy bay vd tdu chiin chuyen ddng cimg chiiu:
- Phuong trinh C£> cua bom theo Ox vd Oy:
, , X 1 J 1 x ' X = V , . t = > t = — ; y = - g t ^ = - - g _
V, 2 2 V;
- Vi tri bom trdng mue tidu Id tog dd x, cda bom:
(1) - Phucmg trinh CD cua tdu chiln:
x,=v,.t + I = v , ^ . l = v , l | + l(2)
34 • TillP CHi THlflBI GIAO DMC-S6106-6/2014
NGHIEN CUU & UNG DUNG
- E>l bom trdng muc tieu thi; x, = x^, tir (1) vd (2) suy ra:
/ = ( V , - V ; ) .
b). Trudng hgp may bciy vd tdu chien chuyen dgng ngugc chieu:
- Phuong trinh chuyin ddng eiia tdu chign:
X^ =l-V^X = l~V2
n
(3)- Bom roi trung mye tieu khi
>l = (v,-fv,), 2h
. X = v^J = Vo c o s a i => I = (1)
• y = - - g t ' - f v , , t = - - g t = - l - ( v , s i n a ) t (2) 1 gx" - + t a n a . x (3) 2vl cos^ a
d hai vj trl B vd C, dlu ed y = h. The y = h vdo (3):
1 gx"
- + tana.x = 2 v^ cos^ a
2hVnCos'a = -gx^ + 2sinacosa.vJ.x (4)
x = - v^sinacosa+v^cosai/v^sin'a-2gh (5)
••y ,.( X
Thl dtf 4: Mpt chiln sj dgt sdng cli dudi mdt cdn him cd dd sdu h. Hdi phdi d^t sung edeh mi|ng him mdt khodng / Id bao nhieu so vdi phuong ngang dl tim xa x eiia dgn trgn mat dit la Idn nhit? Tinh tim xa nay, bilt vdn tdc eua dan khi rdi ndng sung 14 V,.
Luffl: giai:
Phtrcmg trinh cua dgn theo phuang Ox & Oy:
Tai B mudn tam xa BC ciic dai thi: P = 45"
= > v . . = v „ = > v L = v J , Vdi:
v^ = Vp.cosa = const
< - < = - 2 g h
= Vg cos^ a yl, = v j s i n ' a - 2 g h
=> vl cos^ a - v^ sin^ a = -2gh . 2 - 2 g h
=>cos a - s i n a = —f—, v^
Nhung:
cos a sin^ a -t- cos^ a = 1 =
Thay (6) v&o (5) ta dugfc:
1 gh '2 v;
i^gh
2 v!
. (6)
= ' ' = ^ I J T
g'h' 1 ^ gh v' 2 v^— ^l^'i-f
2 v HThi dM 5: Mdt vien dgn dupe ban ra khdi ndng sung vdi van tdc 1500ft/s, ban vao mye tieu (bia B) cdch xa 150ft. Hdi ndng siing phdi hudng vdo dilm A cao hon bia bao nhieu dl ban trung bia.
Lupc giai:
Phan tieh chuyin dgng eiia dgn thdnh hai thdnh TAP CHi THlfTBIGlAO DUC-S6 106-6/2014 • 35
NGHIEN CUU & UNG DUNG
phan doc theo hai tryc Ox vk Oy:
x = V|,cosa.t=>t = (1)
y = v „ s i n a . t - - g t ' = t ( v , s m a — g t ) P) (g = 9,8m/s'=32,15ft/s'»32,2ft/s') Khi dan trung myc tieu thi y = 0. Tir (2)
=*t = 0 ( l o , i ) v a / = ^^iL!!£^(3) g
Thay (3) vao (1) vathay cae sd ligu da cho vao (l)taduae:
=> a =-arcsin(2,14.10"') = 1,07.10"'rad 2
AB = OBtan a = x.tan a = 49mm
x^ = OA COS 70° = 20700 x 0,3420 = 7080m y 4 = 0 A sin 7 0 ° = 19450m
V4nt6ct?iA:
ds
dt = at = 46x30 = 1380m/s.
O
N6ng sung phai dat cao han bia 49 mm.
Thi du 6: Mpt ten ilia dirge ph6ng len tir trang thdi dihig ygn, chuygn d6ng theo mot ducmg thSng Chech 70" so vdi phuong ngang vk vdi gia t6c 46m/s^
Sau 30s thl dOng ca day ngCmg hoat d$ng vk t6n lua chuySn dpng theo mOt dudng parabol trd Ip Tt^i DSt.
Gia sir gia tdc roi ty do li 9,8m/s^ tren loan bp dudng bay vk anh hudng cua Ichong khi lil cd thg bo qua.
a). Tim thdi gian bay tir khi phdng tdi khi eham dat?
b). Dp cao eye dai mk ten lua dat dirge \k bao nhigu?
c). Khoang each tir noi phdng dgn digm eham dit 14 bao nhigu?
Lu-Q-c piai
a). QuSng dudng OA tgn lua di trong 30 giay dau tien la
s = OA = - a t ' = 20700m = 20,7km.
2
Cac thanh p h ^ c6a Vg:
v„, = v„.cos 70° = 1380x0,3420 = 472m/s
^v^=v„.sin70°=1380x0,9397 = 1297m/s Bai toan bay gid la tgn h ^ duyc phdng t^i A vdi vSn tdc diu la Vgt^o vdi phuong ngang mOt gdc a = 70 . Ngu lay gdc thdi gian la lue ten lljra t?i A thi phuang trinh chuygn dpng cua tgn lira la
X = Xj+V|, cos a.t = 7 0 8 0 + 472.t (1) y = yA+VoSma.t—gt' =19450+1297t-4,9t' (2)
Khi ch?m dat y = 0. Giai (2) vk gift lgi nghi?m duong ta dupe: t =278,3s.
Thdi gian tir Iflc phdng tdi khi tgn Ida ch^m dat la: t| - 30 + 278,3 = 308,3s.
TojdOcuaA:
O XA
bj.Tacd: v^ = v „ s i n a - g r = 1297-9,8/
Khi tgn lu-a d do cao eye d^i:
v^ = v „ s i n a - g t = 1297-9,8t = 0
=>t = 132,3s Thay t v a o ^ ) ta du^ic:
y ^ ' l O S Z ' o O m " 105,2km.
e). Khoang cdch tir nai phdng dgn ndi ch^m dat la (thay t = 278,3s vao (1))
X = 7080 + 472 X 278,3 = 138,7km.
n i . KtTLUAN ' TAP CHi THifr BI GIAO DgC- Sd 106 - 6/2014
[; Chuyin ddng ndm Id mOt chuyen ddng phue tgp, nhOmg bilu hi?n cua nd diln ra trong ddi sdng Id mudn hinh, mudn ve. Chuyin dgng cua vien dgn khi rdi ndng sung, cda tgn lira luc rdi b? phdng hay ciia qua bdng ten nit khi rdi khdi mdt v9t,.v.v....tit cd dlu Id chuyin ddng ngm. Chuyin ddng ngm thl didn ra phdc tgp, tuy nhidn nhQng dng dung eua cdc kiln thdc vl ehuyin dpng nem lai dugc dp dung rit rdng rai trong mpi ITnh v^re eua cudc sdng eon ngudi.
Vi vdy, trong dgy hpe, ngodi viec trang bj cho hpc sinh nhOng kiln thirc co ban vl chuyin ddng ngm, ngudi gido vign phdi tgo mpi dilu kign dl hpe sinh bilt vd hilu duge nhihig img dung to Idn eiia edc kiln thdc ndy trong cudc sdng. Qua dd, gidp cho cdc em them ySu thich bp mdn vd hdng thu hon trong hoc t|p, td dd gdp phin ndng eao chit lupng dgy - hpe
i^Q^^^^^^^^m I
cua giao vign va hpc sinh a cdc trudng trung hpc phd thdng trong ndi rieng vd cdc trudng phd thdng trong ca nude ndi chung.
Tdi lif u tham khdo
1. Nguyin Thl Khdi - Phgm Qui Tu - Luong Tit Dgt - Lg Ch§n Hung - Nguyin Ngoc Hung - Phgm Dinh Thilt - Bui Trpng Tudn - Le Trpng Tudng. Vdt li lap 10 Nang cao. NXB Gido due - 2006.
2. Phgm Qui Tu - Luong Tit Dgt - Lg Chan Hdng - Bui Trpng Tudn - Lg Trpng Tudng. Hudng ddn lam bdi tgp vd dn tgp vgt li lop 10 ndng cao.
NXB Gido due-2006.
3. Luong Duygn Binh - Phgm Gia Thinh - Nguygn Xuan Chi - Td Giang - Trln Chi Minh - VQ Quang. Vgt li Idp 10 Ban co ban (Sdch thi diem) - NXB Gido dye-2003.
BO THI NGHIEIM MO TA... rr/4,„.„,™„g«>
Trong dgy hpe vdt ly d trudng phd thdng, ta cd thl sd dyng thi nghiem ndy de khing dinh eho hpc sinh (HS) thiy ring chuyin dpng roi tu do ed phuang thang ddng trong khi dgy bdi "sy roi tu do eua vgt"
v|t IJ 10 vd giai thich djnh tinh hi?n tupng xdy ra, vi?c cung cd kiln thdc cho HS bing thi nghigm sg gidp cho HS ddo sdu vd tin tudng kien thirc hem.
Trong dgy hpe v§t Iy dgi cuong d bge dgi hpc, ta ed the su dung thf nghiem ndy dg ddt vin de vao bdi cho cde bdi lien quan den chuygn dpng quay ciia v$t rin vd roi tu do. Thi nghiem cung cd thl dimg dl cung cl kiln thde cua sinh vign (SV) vl-mdmen quay, mdmen qudn tinh, v§n tdc, gia tdc chuygn ddng cua v§t. Thi nghi?m ciing dupe su dyng nhu mpt dgng bdi t§p Ihi nghifm dl tim dilu ki$n vign bi roi vdo eh§u (tim bign dO gde a). Ngodi ra, SV cung cd thl v(ln dyng nhdng kiln thdc vl dpng hpc, dpng \\ic hpc dl gidi thich djnh tinh vd djnh lupng kit qua thi nghi$m.
Bp thi nghiem eung gdp phin kich thich tinh td md, hilu ki, hilu dpng cua (SV), tdng mde dp hung thd eiia S V trong gid hpe, giup SV ed tdm nhin phong phii, da dgng hon vl nhflng kiln thdc md giap vien (GV) va gido trinh cung cip.
2. Kit lu9n
Ddy Id bd thi nghiem t\r tgo don gidn, de th\je hi$n, dl thdnh cdng nen GV cd Ihl td chuc hudng
ddn cho HS, SV ty thiet kg vd tign hdnh thi nghi?m.
Kit qud thf nghifm dupe gidi thieh ehi tigt, rd rdng, ed dinh tinh Idn dinh lupng, giup eho GV, SV vd HS hiiiu rd ban chdt vd hi?n tugng vdt Ij? xdy ra trong thi nghi?m.
Bd thi nghiem ndy khdng nhChig gdp phin Idm phong phu, da dang thilt bi day hpe, md cdn Id mpt tdi li§u tham khdo bd Ich cho ca GV, SV vd HS.
Tdi li^u tham khao
1. Luong Duygn Binh (2004), Vdt ty dai ctrong -rdp A NXB Gido dye.
2. Clemens Berthold (2006), Physikatische Freihand-experimenle, Aulis Verlag Deubner.
3. Trdn Thj Thanh Thu (2007), Khai thdc vd sit dung thi nghiem ty tgo trong dgy hgc phdn Co hgc Vdt li dai cuang, Lugn vdn thgc sT - Trudng DHSP Hul.
4. Trdn Thj Thanh Thu, Phdi huy linh lich cue vd sdng Igo ciia SV vdt li thdng qua ihi nghiem tu lao. Tap chi Thilt bj giao dye, sd 78, thdng 2 - 2012.
5. Trin Thj Thanh Thu, Gidi ihi^u bg thi nghiim chuyin dgng quay ciia vgt rdn irong dgy hgc vgt ly dgi cuang, Tgp chi Gido dye Sd dac bi?t, thdng 12 -2012.
TAP CHI THlfTBI GIAO DMC-SO 106-6/2014 • 31
