Ntchito yochitidwa ndi mphamvu
1.1 Tanthauzo la Ntchito
Ngati muikankhira buku pamwamba pa tebulo mpaka buku litasunthika, mumauzidwa kuti mwagwira ntchito pa bukulo. Ngati chinthu chagwa pansi chifukwa cha kukoka kwa mphamvu yokoka, mphamvu yokoka imanenedwa kuti yagwira ntchito pa chinthucho. M'malo mwake, ngati muikankhira chinthu ndi mphamvu zanu zonse mpaka kutuluka thukuta kwambiri, koma chinthucho sichikusuntha konse, mumanenedwa kuti simunagwire ntchito pa chinthucho. M'moyo watsiku ndi tsiku, anthu anganene kuti mwagwira ntchito molimbika pokankhira chinthucho koma mu Fizikiki, simugwira ntchito pa chinthucho chifukwa palibe kusunthika kwa chinthucho.
Ntchito pa chinthu ikhoza kuchitidwa ndi mphamvu yosasintha (kuchuluka ndi malangizo ake ndi osasintha) kapena mphamvu yosinthasintha (kuchuluka ndi malangizo ake zimasiyana). Mphamvu yokoka, yomwe imagwira ntchito pa chinthucho pamene chinthucho chili pafupi ndi nthaka. Chinthucho chikakhala kuti chikugwa momasuka pafupi ndi nthaka, kuchuluka ndi malangizo a kufulumira kwa kugwa kwa chinthucho ndi osasintha chifukwa kuchuluka ndi malangizo a mphamvu yokoka yomwe ikufulumizitsa chinthucho ndi osasintha. Mphamvu yosasintha (koma yokhala ndi malangizo osasintha) ndi mphamvu ya masika . Chitsanzo china ndi roketi yomwe yaponyedwa mumlengalenga kapena kubwerera padziko lapansi. Roketi ikaponyedwa, kuchuluka kwa mphamvu yokoka yomwe ikugwira ntchito pa iyo kumasintha motsatizana ndi mtunda wa sikweya kuchokera pakati pa dziko lapansi.
1.1.1 Ntchito yochitidwa ndi asilikali okhazikika
Mwa masamu, ntchito yochitidwa ndi mphamvu yosalekeza pa chinthu imatanthauzidwa ngati kusamuka kochulukitsidwa ndi mphamvu kapena gawo la mphamvu lomwe lili ndi njira yofanana ndi kusamuka kwa chinthucho. Yang'anani chinthu pamwamba pa ndege yosalala yozungulira ndi kusamuka kumanja koyambitsidwa ndi mphamvu yokankhira (F).
Chithunzi 1. (Pamwamba) Njira yoyendetsera chinthucho ndi yofanana ndi mphamvu F. (Pansi) Njira yoyendetsera chinthucho ndi yofanana ndi gawo la mphamvu F m'njira yopingasa (F cos).
Ntchito yochitidwa ndi mphamvu yosonkhezera (F) ndi iyi:
W = (F)(s)(cos θ) = F s (cos 0) = F s (1)
W = F s
Ntchito yochitidwa ndi gawo la mphamvu F mopingasa (F cos θ) ndi:
W = (F cos θ)(s)(cos 0) = (F cos )(s)(1)
W = F s cos θ
Ntchito yochitidwa ndi mphamvu ya kinetic frictional (f k ) ndi iyi:
W = (f k )(s)(cos 180) = (f k )(s)(-1)
W = – (f k )(s)
Ntchito yochitidwa ndi mphamvu yachibadwa (N) ndi:
W = (N)(s)(cos 90) = (N)(s)(0) = 0
Ntchito yochitidwa ndi kulemera (w) ndi:
W = (w)(s)(cos 90) = (w)(s)(0) = 0
Kufotokozera: W = ntchito, s = kuchuluka kwa kusamuka, θ = ngodya pakati pa mphamvu ndi kusamuka.
Chithunzi 2.
(a) Chinthucho chili mu free fall. Kulemera kwake kuli mbali imodzi ndi kusuntha kwake (b) Chinthucho chimayenda molunjika mmwamba. Njira yolemererayo ndi yosiyana ndi njira yosuntha kwake.
Mu chitsanzo chapitachi, ntchito yochitidwa ndi kulemera (w) ili ndi mtengo wa zero chifukwa njira yolowera kulemera kwa chinthucho ndi yolunjika ku njira yolowera kuchoka kwa chinthucho. Tiyenera kudziwa kuti ntchito yochitidwa ndi kulemerayo sidzakhala ndi mtengo wa zero ngati njira yolowera kulemerayo ndi yofanana kapena yosiyana ndi njira yolowera kuchoka kwa chinthucho.
Ntchito yochitidwa ndi kulemera (w) pa chinthu chomwe chili mu kugwa kwaulere chomwe chawonetsedwa pachithunzi a ndi:
W = F s (cos θ) = wh (cos 0) = wh (1) = wh = mgh
Ntchito yochitidwa ndi kulemera (w) pa chinthu chomwe chikuyenda molunjika mmwamba chomwe chawonetsedwa pachithunzi b ndi:
W = F s (cos θ) = wh (cos 180) = wh (-1) = – wh = – mgh
Kufotokozera: w = kulemera (Newton), h = kutalika (mita), m = kulemera (kg), g = kuthamanga kwa mphamvu yokoka (mita pa sekondi imodzi).
Malinga ndi kufotokozera kwapita, mfundo zotsatirazi zaperekedwa: Choyamba, ngati chinthu sichikusuntha, mphamvu yomwe imagwiritsidwa ntchito pa chinthucho sigwira ntchito iliyonse. Ngati s = 0, W = 0; Chachiwiri, ngati mphamvu ipanga ngodya yoperekedwa kusuntha kwa chinthucho , gawo la mphamvu lokhalo lomwe likugawana njira yomweyo ndi kusuntha kwa chinthucho ndi lomwe limagwira ntchito pa chinthucho; Chachitatu, mphamvu yomwe ili mbali imodzi yolunjika kunjira yosuntha kwa chinthucho ipanga ngodya ya 90 o . Cos 90 = 0; Chachinayi, ntchito ikhoza kukhala ndi chizindikiro chabwino kapena choipa. Ngati mphamvuyo ili mbali imodzi ndi kusuntha kwa chinthucho ndipo imapanga ngodya ya 0 o , imagwira ntchito yabwino pa chinthucho. Mosiyana ndi zimenezi, ngati mphamvuyo ili ndi njira yosiyana ndi njira yosuntha kwa chinthucho ndipo imapanga ngodya ya 180 o , imagwira ntchito yoipa pa chinthucho.
Chithunzi 3. Mphamvu (F) – chithunzi cha kusuntha (s). Ntchito ndi yofanana ndi malo okhala ndi mthunzi.
Ntchito yomwe imachitika ndi mphamvu yosalekeza pa chinthu pamene chinthucho chikusunthika ndi yofanana ndi malo omwe ali mumthunzi mu graph ya mphamvu (F) - malo (s).
Ntchito imatchedwa W (zilembo zazikulu), ndipo kulemera kumatchedwa w (zilembo zochepa). Gawo la SI la ntchito ndi Newton ∙ mita (N m). Ndi lofanana ndi Joule, chidule chake ndi J.
Dzina lake linatchedwa motero polemekeza dokotala wa ku Britain wa m'zaka za m'ma 19 , James Prescott Joule.
Chitsanzo cha funso 1: Ntchito yochitidwa ndi mphamvu yosalekeza
Chinthu chili pamalo opumulira pamwamba pa pansi popanda kukangana. Pa chinthucho pamakhala mphamvu ya 10 N, kupanga ngodya ya madigiri 30 motsutsana ndi pansi. Ngati chinthucho chikuyenda patali mita imodzi, kodi mphamvuyo imagwira ntchito yochuluka bwanji pa chinthucho?
yankho;
Yodziwika: F = 10 N, s = mita imodzi
Akufuna: Ntchito (W)
W = (F)(s)(cos 30 o ) = (10 N)(1 m)(1/2 √ 3) = 5 √ 3 N m
Chitsanzo cha funso 2: Ntchito ndi mphamvu yosalekeza
Kokonati ya 0.2 kg imakhala yofewa kuchokera pamtunda wa mamita 10 kuchokera pamwamba pa nthaka. Ngati mphamvu yokoka ndi 10 m/s 2 , kodi kokonati imagwiridwa ntchito yochuluka bwanji potengera kulemera kwake?
yankho;
Zodziwika: m = 0.2 kg, h = 10 m, g = 10 m/s 2
Kufunidwa: Ntchito (W) potengera kulemera (w)
W = F s = wh = mgh = (0.2 kg)(10 m/s 2 )(10 m) = 20 kg m 2 /s 2 = 20 N m = 20 Joules
1.1.2 Ntchito ndi mphamvu zosinthasintha
Chitsanzo cha mphamvu yosinthasintha ndi mphamvu ya masika. Kuchuluka kwa mphamvu ya masika kumasintha nthawi zonse. Chifukwa chake, ntchito yochitidwa ndi mphamvu ya masika pa chinthu sichingathe kuwerengedwa pogwiritsa ntchito njira yogwirira ntchito ya mphamvu zosasintha (W = F s cos θ). Ngati kasupe watambasulidwa, kasupe watambasulidwa kwambiri, mphamvu yogwira imafunika kuti kasupeyo atasulidwe kwambiri. Ndipo ngati kasupe wapanikizidwa, kasupe wapanikizidwa kwambiri, mphamvu yopondereza imafunika kwambiri. Kasupe wapanikizidwa kapena kutambasulidwa, mphamvu ya masika imasintha kuchokera pa 0 (x = 0) kufika pamtengo wapamwamba kwambiri (F = kx). Chifukwa chake, kuchuluka kwa mphamvu ya masika kumawerengedwa pogwiritsa ntchito avareji. Kuchuluka kwa mphamvu ya masika ndi:
Ntchito yochitidwa ndi mphamvu ya masika pa chinthu ndi iyi:
W = ntchito, x = Δx = kupotoka kwa masika (mita), F = mphamvu ya masika (Newton).
Chitsanzo cha funso 3: Ntchito ndi mphamvu yosinthasintha
Pa kasupe pali kulemera kolendewera kolemera makilogalamu 1, kotero kasupeyo amatambasuka ndi masentimita 2. Ngati mphamvu yokoka ndi 10 m/s 2 , dziwani (a) mphamvu yokoka (b) ntchito yochitidwa ndi mphamvu yokoka pa kulemerako.
yankho;
Yodziwika: m = 1 kg, g = 10 m/s 2 , x = Δx = 2 cm = 0.02 m.
(a) kasupe wokhazikika
(b) ntchitoyo idachitika ndi mphamvu ya kasupe pa kulemera
W = -1/2 kx 2 = -1/2 (500)(0.02) 2 = – (250)(0.0004) = -0.1 Joule
Ntchito yochitidwa ndi mphamvu ya kasupe pa kulemera ili ndi phindu loipa chifukwa njira ya mphamvu ya kasupe ili yosiyana ndi njira yomwe kulemera kumasunthira (mphamvu ya kasupe ili mmwamba, kulemera kuli pansi).
1.2 Ntchito Yogwira Ntchito Pa Intaneti Kapena Ntchito Yogwiritsidwa Ntchito ndi Gulu Logwira Ntchito Pa Intaneti
Ngati pali mphamvu imodzi yokha yomwe imagwira ntchito pa chinthu pamene chinthucho chikusunthika, ntchito yochitidwa ndi mphamvu ya ukonde ndi yofanana ndi ntchito yochitidwa ndi mphamvuyo. Mwachitsanzo, ngati chinthucho chili mu kugwa kwaulere ndipo kuletsa mpweya sikunyalanyazidwa, mphamvu yokhayo yomwe imagwira ntchito pa chinthucho ndi mphamvu yokoka. Pankhaniyi, mphamvu ya ukonde yomwe ikugwira ntchito pa chinthucho ndi mphamvu yokoka (onani chithunzi 2).
W ukonde = W mphamvu yokoka
Ngati mphamvu zina zikugwira ntchito pa chinthu pamene chinthucho chikusunthika, ntchito yochitidwa ndi mphamvu ya ukonde ndi yofanana ndi ntchito ya ukonde yochitidwa ndi mphamvu zonse zomwe zikugwira ntchito pa chinthucho (onani chithunzi 1).
W net = W 1 + W 2 + W 3 + W 4
Ntchito yomwe mphamvu ya neti imagwira pa chinthu ingawerengedwenso mwa kupeza mphamvu ya neti poyamba kenako nkuichulukitsa ndi kuchuluka kwa kusuntha.
W = ΣF s
Chitsanzo cha funso 4: Netiweki
Bokosi losasunthika pamwamba pa pansi limakankhidwa ndi mphamvu ya 20 N mpaka bokosilo litasuntha mtunda wa mita imodzi. Ngati mphamvu yosonkhezera ili mbali yomweyo ndi kusuntha kwa bokosilo ndipo pa bokosilo likugwira ntchito mphamvu yokangana ya 2 N, dziwani kuchuluka kwa ntchito yolumikizidwa ndi mphamvu yolumikizidwa pa bokosilo.
yankho;
Yodziwika: F = 20 N, f k = 2 N, s = 1 m
W 1 = F s = (20 N)(1 m) = 20 Nm = 20 Joules
W 2 = f ks = – (2 N)(1 m) = – 2 Nm = – 2 Joules
Ntchito yapaintaneti kapena ntchito yochitidwa ndi gulu lankhondo
Ukonde = W 1 – W 2 = 20 J – 2 J = 18 J
Chitsanzo cha funso 4) Mphamvu yokakamiza (F) imagwira ntchito yabwino, mphamvu yokangana ya kinetic (f k ) imagwira ntchito yoyipa
