Ngati mutakankhira buku patebulo mpaka litasuntha, mukugwira ntchito pa bukulo. Chinthu chikagwa padziko lapansi chifukwa chakuti chakokedwa ndi mphamvu yokoka , mphamvu yokoka imagwira ntchito pa chinthucho. Mosiyana ndi zimenezi, ngati mutakankhira chinthu ndi mphamvu zanu zonse mpaka mutanyowa ndi thukuta koma chinthucho sichisuntha, simunagwire ntchito pa chinthucho. M'moyo watsiku ndi tsiku, amati mwagwira ntchito mwakhama kapena mwagwira ntchito molimbika kukankhira chinthu, koma malinga ndi sayansi, simunagwire ntchito pa chinthucho chifukwa chinthucho sichimasuntha (chinthucho sichisintha malo).
Ntchito ikhoza kuchitidwa ndi mphamvu yosasintha (kukula ndi malangizo a mphamvu nthawi zonse zimakhala chimodzimodzi) kapena mphamvu yosinthasintha (kukula ndi malangizo a mphamvuyo kusintha). Chitsanzo cha mphamvu yokhala ndi kukula kosasintha ndi malangizo ndi mphamvu yokoka yomwe imagwira ntchito pa chinthu chomwe chili pafupi ndi dziko lapansi. Chitsanzo cha mphamvu yokhala ndi kukula kosasintha ndi malangizo ndi mphamvu ya kasupe. Ngati mutambasula kasupe, mukamatambasula kwambiri, mumakoka molimbika, motero kukula kwa mphamvuyo sikusinthasintha pamene kasupe akutambasula. Chitsanzo china ndi pamene roketi ikupita mumlengalenga, ikakhala kutali ndi dziko lapansi, mphamvu yokoka ya dziko lapansi imagwira ntchito yochepa pa roketi.
1.1 Ntchito yochitidwa ndi mphamvu yosalekeza
Mwa masamu, ntchito yochitidwa ndi mphamvu yosalekeza pa chinthu ndi chipatso cha kusamutsidwa chinthu chokhala ndi mphamvu kapena gawo la mphamvu lomwe lili mbali imodzi ndi kusuntha kwa chinthucho.
Ntchito yochitidwa ndi mphamvu yokankhira (F):
W = (F)(s)(cos θ) = F s (cos 0) = F s (1) = F s
Ntchito yochitidwa ndi gawo la mphamvu F mbali yopingasa (F cos θ):
W = (F cos θ)(s)(cos 0) = (F cos θ)(s)(1) = F s cos θ
Ntchito yochitidwa ndi mphamvu ya kinetic friction (fk):
W = (fk cos θ(s)(cos 180) = (fk )(s)(-1) = – fk s
Ntchito yochitidwa ndi mphamvu yachibadwa (N):
W = (N)(s)(cos 90o) = (N)(s)(0) = 0
Ntchito yochitidwa ndi mphamvu yokoka (w):
W = (w)(s)(cos 90o) = (w)(s)(0) = 0
Kufotokozera: W = khama kapena ntchito (Joules), s = kusamuka (mita), θ = ngodya yopangidwa ndi mphamvu yokhala ndi kusamuka
Mu chitsanzo chapitacho, ntchito yochitidwa ndi mphamvu yokoka (w) ili ndi mtengo wa zero chifukwa njira ya mphamvu yokoka ndi yolunjika (yomwe imapanga ngodya ya 90°)o) ndi njira yosunthira (njira yoyendera) ya chinthucho. Tiyenera kudziwa kuti ntchito yochitidwa ndi kulemera si zero ngati njira ya mphamvu yokoka ili yofanana kapena yosiyana ndi njira yosunthira.
Ntchito yochitidwa ndi mphamvu yokoka (w) pa chinthu chomwe chikugwa momasuka pachithunzi a ndi iyi:
W = F s (cos θ) = wh (cos 0) = wh (1) = wh = mgh
Ntchito yochitidwa ndi mphamvu yokoka (w) pa chinthu chomwe chikukwera molunjika pachithunzi b ndi iyi:
W = F s (cos θ) = wh (cos 180) = wh (-1) = -wh = -mgh
Kufotokozera: w = kulemera (Newton), h = kutalika (mamita), m = kulemera (kg), g = kuthamanga chifukwa cha mphamvu yokoka (mamita pa sekondi imodzi yozungulira sikweya)
Kutengera ndi kufotokozera kwapitako, mfundo zotsatirazi zitha kutsimikizika:
Choyamba, ngati chinthucho sichikusuntha, ndiye kuti mphamvu yomwe ikugwira ntchito pa kusunthako sigwira ntchito. Ngati s = 0 ndiye kuti W = 0.
ChachiwiriNgati mphamvuyo ikupanga ngodya inayake ku kusuntha kwa chinthucho, ndiye kuti gawo la mphamvuyo lokhalo lomwe lili kumbali yosuntha kwa chinthucho ndi lomwe limagwira ntchito pa chinthucho.
Chachitatu, mphamvu yolunjika ku kusuntha kwa chinthu sigwira ntchito iliyonse pa chinthucho. Ngati mphamvuyo ili yolunjika ku kusuntha, ngodya yopangidwa ndi 90°o. Cos 90o = 0.
ChachinayiKhama likhoza kukhala labwino kapena loipa. Ngati mphamvu ili mbali imodzi ndi kusuntha kwa chinthucho, ngodya yopangidwa ndi 0o ndiye kuti mphamvuyo imagwira ntchito bwino, mosiyana ngati mphamvuyo ili mbali ina ya kusuntha kotero ngodya yopangidwa ndi 180o Kenako mphamvuyo imagwira ntchito yotsutsa pa chinthucho.
Ntchito yochitidwa ndi mphamvu yosalekeza pa chinthu pamene chinthucho chikusuntha ndi yofanana ndi malo omwe ali mumthunzi mu graph ya mphamvu (F) ndi kusuntha (s).
Chizindikiro cha ntchito ndi W (chilembo chachikulu) pomwe chizindikiro cha kulemera ndi w (chilembo chocheperako). Gawo la machitidwe apadziko lonse lapansi la ntchito ndi Newton meter (N m). Dzina lina la Newton meter ndi Joule, chidule cha J, lotchedwa polemekeza katswiri wa sayansi ya zaku Britain wa m'zaka za m'ma 19 James Prescott Joule.
1.2. Ntchito yochitidwa ndi mphamvu yosasinthasintha
Chitsanzo chimodzi cha mphamvu yosinthasintha ndi mphamvu ya masika. Kukula kwa mphamvu ya masika kumasintha nthawi zonse, kotero ntchito yochitidwa ndi mphamvu ya masika pa chinthu sichingathe kuwerengedwa pogwiritsa ntchito njira ya ntchito yochitidwa ndi mphamvu yosasintha.
Ngati kasupe watambasulidwa, kasupe akatalika, mphamvu yake imafunikira kukhala yaikulu. Mofananamo, mosemphanitsa, kupanikizika kwambiri kukanikizidwa, mphamvu yake imakhala yochepa kwambiri kasupe akali, mphamvu yake imafunikira kukhala yaikulu. Malinga ngati kasupe watambasulidwa kapena kukanidwa, mphamvu yake imasintha kuchoka pa 0 (x = 0) kufika pamlingo wapamwamba (F = kx) kotero mphamvu yake imawerengedwa pogwiritsa ntchito avareji. Mphamvu yake yapakati ya kasupe ndi:
F = ½ (0 + kx) = ½ kx
Ntchito yomwe mphamvu ya masika imagwirira ntchito pa chinthu ndi iyi:
W = F x = ½ kx2
Kufotokozera: W = ntchito (mayunitsi a Joules), x = kuwonjezeka kwa kutalika kwa masika (mayunitsi mamita), F = mphamvu ya masika (mayunitsi a Newton).
2. Ntchito yochokera ku zotsatira zake kapena ntchito yonse (ntchito yochitidwa ndi mphamvu yonse)
Ngati pali mphamvu imodzi yokha yomwe ikugwira ntchito pa chinthu panthawi yosuntha kwake, ndiye kuti ntchito yonse yomwe imachitika ndi mphamvu yonseyo ndi yofanana ndi ntchito yomwe imachitika ndi mphamvuyo. Mwachitsanzo, pamene chinthu chili mu kugwa kwaulere ndipo kukana mpweya sikunyalanyazidwa, mphamvu yokhayo yomwe ikugwira ntchito pa chinthucho ndi mphamvu yokoka.
W = Wmphamvu yokoka
Ngati pali mphamvu zingapo zomwe zikugwira ntchito pa chinthu pamene chinthucho chikuyenda, ndiye kuti ntchito yonse yomwe yachitika ndi mphamvu yonseyo ndi yofanana ndi kuchuluka kwa ntchito yonse yomwe yachitika ndi mphamvu zonse zomwe zikugwira ntchito pa chinthucho.
W = W1 +W2 +W3 + … + Wn
Ntchito yochitidwa ndi mphamvu zingapo zomwe zimagwira ntchito pa chinthu ikhozanso kuwerengedwa pofufuza kaye kukula kwa mphamvu yonse kenako n’kuichulukitsa ndi kukula kwa kusamuka.
W = (Mphamvu yochokera)(kusamuka) = (zotsatira F(s)
