1. Te whakamāramatanga o te kaha waku
Ko te waku he tōia e mahi ana i waenga i ngā mata o ngā mea e pā ana tetahi ki tetahi. I roto i tēnei kaupapa, ko te kaha waku e akohia ana e pā ana ki te kaha waku e mahi ana i waenga i ngā mata tinana totoka e rua e pā ana. Pērā i te waku i waenga i te turanga o te kurupae me te mata o te papa, te waku i waenga i te turanga hū me te mata o te papa, te waku i waenga i ngā wira o te motuka me te mata o te rori.
Ka mahi tonu te kaha waku i runga i te mata o ngā mea totoka e pā ana tetahi ki tetahi, ahakoa he tino maeneene ngā mea. Ahakoa ngā mata maeneene he tino taratara i runga i te tauine moroiti. Ina neke tetahi mea, ka whakararuraru ēnei koki moroiti i te nekehanga. I te taumata ngota, ka puta te pupuhi i runga i te mata ka tata rawa ngā ngota ki ētahi atu mata, kia taea ai e ngā kaha hiko i waenga i ngā ngota te hanga hononga matū, hei hononga i waenga i ngā mata e rua o tetahi mea neke. Ina neke tetahi mea, hei tauira, ina panaia e koe he pukapuka ki runga i te mata o te tēpu, ka pāngia te nekehanga o te pukapuka e ngā arai, ā, ka mutu. Nā te hanganga me te tukunga o te hononga tēnei.
Ki te mirimiri te mata o tētahi mea ki te mata o tētahi atu mea, ka mahi ia mea i runga i te waku i waenganui i a rātou anō. Ko te kaha waku i runga i te mea neke kei te taha kē tonu i te ahunga o te nekehanga o te mea. Haunga te aukati i te nekehanga o ngā mea, ka taea e te waku te whakararu me te pakaru. Ka kitea tēnei i runga i te miihini waka. Hei tauira, ina tukuna e tātou he hinu whakahinuhinu ki te miihini motopaika, e hiahia ana tātou ki te whakaiti i te kaha waku e puta ana i roto i te miihini. Ki te kore e tukuna te hinu whakahinuhinu, ka tere te pakaru o tā tātou miihini waka. Ko tēnei tauira tētahi o ngā ngaronga i puta mai i te waku.
Tuhinga o mua ngā kaha waku
E rua ngā momo kaha waku, arā, ko te kaha waku pumau (fs ) me te kaha waku nekeneke (fk ) . Ka mahi te kaha waku pumau ina kore te mea e neke, ko te kaha waku nekeneke ia ka mahi ina neke te mea. Ki te pana koe i tētahi tēpu, engari kāore te tēpu i neke, ko te kaha waku e pā ana ki te tēpu e okioki ana he kaha waku pumau. I tetahi atu taha, ina neke te tēpu, ko te kaha waku e pā ana ki te tēpu he waku nekeneke. Ki te kore te tēpu e nekehia tonutia, ka mutu te tēpu i muri i te neke mō tētahi wā. Ka mutu te tēpu nā te kaha waku nekeneke e aukati ana i te nekehanga o te tēpu.
Kua paheke koe i te wā e takahi ana koe i tētahi mea maeneene? Ina paheke koe, ko te kaha waku e mahi ana i waenga i te turanga o te hū, i te raro rānei o te hu he mata maeneene, ko te waku nekeneke. He rite tēnei raruraru ki te wā e neke ana te motopaika, te motuka rānei i runga i te mata rori mākū, maeneene hoki, e pēhi ana i te wira kia paheke noa. Ina paheke ngā wira, ko te kaha waku e mahi ana i runga i te mata o te wira me te mata rori he kaha waku nekeneke. I tetahi atu taha, ina hikoi koe, ko te kaha waku e mahi ana i waenga i te turanga hū, i te raro rānei o ngā hu me te mata o te papa he kaha waku pumau. Waihoki, ina kore ngā wira e paheke, ko te kaha waku e mahi ana i runga i te mata o te wira me te rori he waku pumau.
2.1 Te kaha waku pumau
Ko te kaha waku pateko he kaha waku e pā ana ki te mata o ngā mea e pā ana tetahi ki tetahi i te wā kāore anō kia nekehia.
E whakaatu ana te Pikitia 1 i tētahi mea kei runga tonu i te mata o tētahi papa papatahi. Mēnā kāore anō kia neke te mea, he iti ake te kaha waku tūmau (fs) i te kaha kukume (F). Mēnā ka tōia tonutia, ka neke te mea. Ina neke te mea matau, ko te rahi o te kaha waku tūmau (fs) e ōrite ana ki te rahi o te kaha kukume (F).
E ai ki te Ture Tuatahi a Newton, ka noho okioki ngā mea mēnā he kore te kaha katoa (te kaha hua).
ΣF y = 0 (Kia okioki te mea, kaua e neke poutū)
N – w = 0
N = w (1.2)
Whakakapia a N i te whārite 1.1 ki a N i te whārite 1.2
f s = μ s w
fs = μs mg ( 1.3)
fs = te waku pumau (N), μs = te tauwehenga o te waku pumau, N = te kaha noa (N), w = te kaha ā-papatipu (N), m = te papatipu (kg), g = te whakaterenga o te kaha ā-papatipu (m/ s² )
Ki te hiahia koe ki te whakatau i te tauwehenga o te waku pateko, whakamahia te whārite 1.1 b
Σf x = 0 (Ka okioki te mea, ā, kāore e neke i te taha whakapae)
F – fs = 0
F = fs ( 1.4)
Ina tīmata te neke o te mea, ka ōrite te kaha waku pūmau mōrahi ki te rahi o te kaha pana, te kaha kume rānei.
2.2 Te kaha waku nekeneke
Ko te kaha waku nekeneke ko te kaha waku e pā ana ki te mata o ngā mea e pā ana tetahi ki tetahi i te wā e neke ana tetahi mea.
Ki te hiahia koe ki te whakatau i te tauwehenga o te waku nekeneke (μ k ), whakamahia te whārite 1.5 b.
E whakaatu ana te Pikitia 2 i tētahi mea e tōia ana i ia wā, kia neke ai te mea i te tere pumau. Ina neke i te tere pumau, ko te rahi o te kaha waku nekeneke (fk) he rite ki te rahi o te kaha kume (F).
E ai ki te Ture Tuatahi a Newton, ka neke te mea i te tere pumau mēnā he kore te kaha katoa (te kaha hua).
ΣF x = 0 (ka neke ngā mea i te tere pumau i te ahunga whakapae)
F – f k = 0
F = fk (1.6)
Tauira raruraru 1:
Ka tōia e tētahi tauira tētahi kurupae he 1 kg te taumaha kei runga i te mata o te tēpu mā te whakamahi i tētahi dynamometer (he taputapu ine kaha). Ina neke te kurupae, ka whakaatuhia e te dynamometer te tau 2 N. Mena ko te whakaterenga o te kaha ā-papatipu = 10 m/s 2 , whakatauhia (a) te rahi o te kaha waku pumau (b) te tauwehenga o te waku pumau
Rongoā:
Mōhiotia : m = 1 kg, F = 2 N, g = 10 m/s 2 , w = mg = 10 N
(a) fs
Ina neke te hihi, ko te rahi o te kaha waku pumau = te rahi o te kaha kume (whakatairitehia te whārite 1.4). Nō reira, f s = F = 2 N.
(b) μs
f s = μ s w
2 N = (μs ) (10 N)
μs = 2 N / 10 N = 0.2
Tauira raruraru 2:
Ka tōia auautia tētahi kurupae he 1 kg te taumaha kei runga ake i te mata o te tēpu kia neke ai te kurupae i te tere pumau. Ina neke te kurupae i te tere pumau, ka whakaatuhia e te dynamometer te tau 1 N. Mena ko te whakaterenga o te kaha ā-papatipu = 10 m/s 2 , whakatauhia (a) te rahi o te kaha waku nekeneke (b) te tauwehenga o te waku nekeneke
Rongoā:
E mōhiotia ana: m = 1 kg, g = 10 m/s² , F = 1 N, w = mg = 10 N
(a) f k
Ina neke auau te hihi, ina neke rānei i te tere pumau, ko te rahi o te kaha waku nekeneke = te rahi o te kaha kume (whakatairitehia te whārite 1.6).
Nō reira, fk = F = 1 N
(b) μk
f k = μ k w
1 N = (μ k )(10 N)
μk = 1 N / 10 N = 0.1
