Umthetho Wesithathu KaNewton ithi uma into 1 isebenzisa amandla entweni 2 khona-ke into 2 isebenzisa amandla entweni 1. Ubukhulu bamandla amabili buyafana kodwa isiqondiso samandla amabili siphambene. Amandla elilodwa libizwa ngokuthi isenzo, elinye amandla libizwa ngokuthi ukusabela.
Uphawu olungeluhle lubonisa isiqondiso samandla. Isenzo sika-F sihle, kanti ukusabela kuka-F kungabi kuhle. Lokhu kubonisa ukuthi amandla esenzo kanye nokusabela asezindleleni eziphambene.
Yenza ucwaningo ukuze uqonde kangcono umthetho wesithathu kaNewton. Uma une-skateboard, cindezela odongeni umi phezu kwalo. Ngemva kokucindezela odongeni, i-skateboard ibuyela emuva isuka odongeni. Ukucindezela kwakho kuya phambili, kuyilapho i-skateboard ibuyela emuva. Lokhu kukhombisa ukuthi udonga nalo luyakucindezela. Uma ucindezela odongeni, udonga nalo luyakucindezela. Amandla akho okusunduza asebenza odongeni, kuyilapho amandla okusunduza odongeni esebenza kuwe. Amandla amabili ayalingana ngobukhulu kodwa aphambene ngendlela eqondile. Ungabiza amandla elilodwa ngokuthi isenzo kanti elinye ngokuthi ukusabela.
Olunye uvivinyo olungenziwa ukuqhumisa ibhaluni lerabha bese kuthi, ngemva kokuba ibhaluni linwebekile ngenxa yokugcwala umoya, likhulule ibhaluni. Ngemva kokukhululwa, ibhaluni "liyandiza". Isiqondiso sokunyakaza kwebhaluni siphambene nesiqondiso somoya ophuma ebhaluni. Lokhu kungachazwa kanjani? Lapho umlomo webhaluni uvuliwe, ibhaluni lisunduza umoya ngaphandle, futhi ngesikhathi esifanayo, umoya uphinde usunduze ibhaluni. Ukusunduza komoya kubangela ibhaluni ukuba lindize. Ukusunduza komoya kusebenza ebhulokini kanye nokusunduza kwebhaluni kusebenza emoyeni. Womabili la mandla anobukhulu obufanayo kodwa ahlukene.
Cabanga ngesithombe sebhlokhi elilele endaweni ephansi. Amandla avamile asebenza kubhlokhi (N) amandla avamile asetshenziswa yindawo ephansi kubhlokhi. Ngesikhathi esifanayo, ibhlokhi liphinde libe namandla avamile endaweni ephansi (N'). Lawa mandla amabili avamile (N no-N') ayalingana ngobukhulu kodwa aphambene ngendlela futhi asebenza ezintweni ezahlukene. Lokhu kuhlukile ku-N no-w asebenza entweni efanayo, okuyibhlokhi. Ngakho-ke u-N no-N' banamandla okusabela kwesenzo.
