Umsebenzi owenziwe ngamandla
1.1 Incazelo Yomsebenzi
Uma ucindezela incwadi phezu kwetafula kuze kube yilapho incwadi isusiwe, utshelwa ukuthi wenze umsebenzi encwadini. Uma into iwela phansi ngenxa yokudonswa kwamandla adonsela phansi, kuthiwa amandla adonsela phansi enze umsebenzi entweni. Ngokuphambene nalokho, uma ucindezela into ngamandla akho onke uze ujuluke kakhulu, kodwa into ingashukumi nhlobo, kuthiwa awuzange wenze msebenzi entweni. Empilweni yansuku zonke, abantu bangase bathi wenze umsebenzi onzima ngokusunduza into kodwa ku-Physics, awusebenzi entweni ngoba bekungekho ukusunduza kwento.
Umsebenzi entweni ungenziwa ngamandla angaguquki (inani kanye nesiqondiso sawo kungaguquki) noma amandla aguquguqukayo (inani kanye nesiqondiso sawo kuyahlukahluka). Isibonelo samandla anenani kanye nesiqondiso esingaguquki amandla adonsela phansi, asebenza entweni lapho into iseduze nobuso bomhlaba. Lapho into ikwi-free fall eduze kobuso bomhlaba, inani kanye nesiqondiso sokusheshisa kokuwa kwamahhala kwento kungaguquki ngoba inani kanye nesiqondiso samandla adonsela phansi asheshisa into kungaguquki. Isibonelo samandla anenani elingaguquki (kodwa elinesiqondiso esingaguquki) amandla asentwasahlobo . Esinye isibonelo irokhethi ephonswa emkhathini noma ebuyela ebusweni bomhlaba. Lapho irokhethi iphonswa, inani lamandla adonsela phansi asebenza kuyo lishintsha ngesilinganiso esiphambene nebanga lesikwele ukusuka enkabeni yomhlaba.
1.1.1 Umsebenzi owenziwe ngamasosha asebenzayo ngokushesha
Ngokwezibalo, umsebenzi owenziwa amandla angaguquki entweni uchazwa njengokugudluzwa okuphindaphindwe ngamandla noma ingxenye yamandla enesiqondiso esifanayo nokugudluzwa kwento. Buka into ebusweni bendiza eyisicaba eyisicaba enokuhamba ngakwesokudla okubangelwa amandla okusunduza (F).
Umfanekiso 1. (Phezulu) Isiqondiso sokufuduka kwento sifana nesamandla F. (Ngezansi) Isiqondiso sokufuduka kwento sifana nesakhi samandla F endaweni evundlile (F cos).
Umsebenzi owenziwe ngamandla okusunduza (F) uthi:
W = (F)(s)(cos θ) = F s (cos 0) = F s (1)
W = F s
Umsebenzi owenziwe yisakhi samandla u-F ohlangothini oluvundlile (F cos θ) uwukuthi:
W = (F cos θ)(s)(cos 0) = (F cos )(ama)(1)
W = F s cos θ
Umsebenzi owenziwa amandla okungqubuzana kwe-kinetic (f k ) uthi:
W = (f k )(s)(cos 180) = (f k )(s)(-1)
W = – (f k )(s)
Umsebenzi owenziwa amandla avamile (N) uwukuthi:
W = (N)(s)(cos 90) = (N)(s)(0) = 0
Umsebenzi owenziwe ngesisindo (w) uthi:
W = (w)(s)(cos 90) = (w)(s)(0) = 0
Incazelo: W = umsebenzi, s = inani lokufuduka, θ = i-engeli phakathi kwamandla kanye nokufuduka.
Umfanekiso we-2.
(a) Into ikwi-free fall. Isisindo sisehlangothini olufanayo nokususwa (b) Into ihambela phezulu iqonde phezulu. Isiqondiso sesisindo siphambene nesiqondiso sokususwa.
Esimweni esidlule, umsebenzi owenziwe ngesisindo (w) unenani elingu-zero njengoba isiqondiso sesisindo sento siqonde ngqo esiyalweni sokufuduka kwento. Kufanele kuqashelwe ukuthi umsebenzi owenziwe ngesisindo ngeke ube nenani elingu-zero uma isiqondiso sesisindo sifana noma siphambene nesiqondiso sokufuduka kwento.
Umsebenzi owenziwe ngesisindo (w) entweni ekwindla ekhululekile eboniswe esithombeni a uthi:
W = F s (cos θ) = wh (cos 0) = wh (1) = wh = mgh
Umsebenzi owenziwe yisisindo (w) entweni ehamba iqonde phezulu eboniswe kumfanekiso b uthi:
W = F s (cos θ) = wh (cos 180) = wh (-1) = – wh = – mgh
Incazelo: w = isisindo (Newton), h = ukuphakama (imitha), m = isisindo (kg), g = ukusheshisa kwamandla adonsela phansi (imitha ngomzuzwana wesikwele).
Ngokusho kwencazelo yangaphambilini, kufinyelelwa eziphethweni ezilandelayo: Okokuqala, uma into ingezwani nanoma yikuphi ukufuduka, amandla asetshenziswa entweni awenzi msebenzi. Uma u-s = 0, u-W = 0; Okwesibili, uma amandla akha i-engeli ethile eya ekufudukeni kwento , ingxenye yamandla kuphela ehlanganyela isiqondiso esifanayo nokufuduka kwento esebenza entweni; Okwesithathu, amandla aqonde ngqo esiqondisoni sokufuduka kwento azokwakha i-engeli engu-90 o . I-Cos 90 = 0; Okwesine, umsebenzi ungaba nophawu oluhle noma olubi. Uma amandla esendleleni efanayo nokufuduka kwento futhi akha i-engeli engu-0 o , enza umsebenzi omuhle entweni. Ngokuphambene nalokho, uma amandla enesiqondiso esiphambene nesiqondiso sokufuduka kwento futhi akha i-engeli engu-180 o , enza umsebenzi omubi entweni.
Umfanekiso 3. Amandla (F) – igrafu yokufuduka (s). Umsebenzi ulingana nendawo enomthunzi.
Umsebenzi owenziwa amandla angaguquki entweni lapho into idlula ulingana nendawo emthunzini kugrafu yamandla (F) – isikhundla (s).
Umsebenzi ubizwa ngokuthi u-W (osonhlamvukazi abakhulu), kanti isisindo sibizwa ngokuthi u-w (osonhlamvukazi abancane). Iyunithi yomsebenzi ye-SI yi-Newton ∙ meter (N m). Ilingana ne-Joule, efushaniswe ngokuthi u-J.
Yaqanjwa kanjalo ukuze kuhlonishwe udokotela waseBrithani wekhulu le-19 , uJames Prescott Joule.
Isibonelo sombuzo 1: Umsebenzi owenziwe ngamandla angaguquki
Into iphumule phezu kobuso bephansi elingenakho ukungqubuzana. Entweni kusetshenziswa amandla angu-10 N, akha i-engeli engama-degree angu-30 ngokumelene nephansi. Uma into ihamba ibanga elingamamitha angu-1, ungakanani umsebenzi owenziwa amandla entweni?
Isixazululo:
Kwaziwa: F = 10 N, s = 1 imitha
Okufunwayo: Umsebenzi (W)
W = (F)(s)(cos 30 o ) = (10 N)(1 m)(1/2 √ 3) = 5 √ 3 N m
Isibonelo sombuzo 2: Umsebenzi ngamandla angaguquki
I-coconut engu-0.2 kg itholakala ekwindla ekhululekile isuka ekuphakameni kwamamitha ayi-10 ukusuka emhlabathini. Uma ukusheshisa kwamandla adonsela phansi kungu-10 m/s 2 , kungakanani umsebenzi owenziwa ngesisindo ku-coconut?
Isixazululo:
Kwaziwa: m = 0.2 kg, h = 10 m, g = 10 m/s 2
Okufunwayo: Umsebenzi (W) ngesisindo (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 Umsebenzi ngamandla aguquguqukayo
Isibonelo samandla aguquguqukayo amandla entwasahlobo. Inani lamandla entwasahlobo liyashintsha njalo. Ngakho-ke, umsebenzi owenziwa amandla entwasahlobo entweni awukwazi ukubalwa kusetshenziswa ifomula yomsebenzi wamandla angaguquki (W = F s cos θ). Uma intwasahlobo inwetshwa, lapho intwasahlobo inwetshwa kakhulu, kulapho kudingeka amandla okudonsa amakhulu ukuze kwelulwe intwasahlobo. Futhi uma intwasahlobo icindezelwe, lapho intwasahlobo icindezelwe kakhulu, kulapho kudingeka amandla okucindezela amakhulu. Lapho intwasahlobo icindezelwe noma yeluliwe, amandla entwasahlobo ashintsha kusuka ku-0 (x = 0) aye enanini eliphezulu (F = kx). Ngakho-ke, inani lamandla entwasahlobo libalwa kusetshenziswa isilinganiso. Inani elimaphakathi lamandla entwasahlobo yileli:
Umsebenzi owenziwa ngamandla entwasahlobo entweni uthi:
W = umsebenzi, x = Δx = ukuphambuka kwentwasahlobo (imitha), F = amandla entwasahlobo (iNewton).
Isibonelo sombuzo 3: Umsebenzi ngamandla aguquguqukayo
Esiphethwini kunesisindo esilengayo esinesisindo esingu-1 kg, ngakho-ke isiphethwini sinwebeka ngo-2 cm. Uma ukusheshisa kwamandla adonsela phansi kungu-10 m/s 2 , nquma (a) i-spring constant (b) umsebenzi owenziwe amandla esiphethwini esisindweni.
Isixazululo:
Kwaziwa: m = 1 kg, g = 10 m/s 2 , x = Δx = 2 cm = 0.02 m.
(a) isisekelo sentwasahlobo
(b) umsebenzi wenziwa yi-spring force esisindweni
W = -1/2 kx 2 = -1/2 (500)(0.02) 2 = – (250)(0.0004) = -0.1 I-Joule
Umsebenzi owenziwa amandla entwasahlobo esisindweni unenani elibi njengoba isiqondiso samandla entwasahlobo siphambene nesiqondiso sokuhamba kwesisindo (amandla entwasahlobo abheke phezulu, isisindo sibheke phansi).
1.2 Umsebenzi We-Net noma Umsebenzi We-Net Force
Uma kukhona amandla asebenza entweni lapho into idlula, umsebenzi owenziwa amandla aphelele ulingana nomsebenzi owenziwe amandla. Isibonelo, uma into ikwi-free fall futhi ukuvinjelwa komoya kunganakwa, amandla asebenzayo entweni kuphela amandla adonsela phansi. Kulokhu, amandla aphelele asebenza entweni amandla adonsela phansi (bheka isithombe 2).
I-W inethi = i-W amandla adonsela phansi
Uma amanye amandla esebenza entweni lapho into ibhekene nokufuduka, umsebenzi owenziwa amandla e-net ulingana nomsebenzi we-net owenziwe yiwo wonke amandla asebenza entweni (bheka isithombe 1).
I-W inethi = W 1 + W 2 + W 3 + W 4
Umsebenzi owenziwe amandla e-net entweni ungabalwa ngokuthola amandla e-net kuqala bese uwaphindaphinda ngenani lokufuduka.
W = ΣF s
Isibonelo sombuzo 4: Inethiwekhi
Ibhokisi elimile phezu kobuso bephansi licindezelwa ngamandla angu-20 N kuze kube yilapho ibhokisi lihamba ibanga eliyimitha eli-1. Uma amandla okusunduza esendleleni efanayo nokufuduka kwebhokisi futhi ebhokisini kusebenza amandla okungqubuzana kwe-kinetic angu-2 N, nquma inani lomsebenzi wenethi owenziwe amandla enethi ebhokisini.
Isixazululo:
Kwaziwa: 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
Umsebenzi we-inthanethi noma umsebenzi owenziwe ngamandla e-net
Inethiwekhi = W 1 – W 2 = 20 J – 2 J = 18 J
Isibonelo sombuzo 4) Amandla okusunduza (F) enza umsebenzi omuhle, amandla okungqubuzana kwe-kinetic (f k ) enza umsebenzi omubi
