He tuhinga mō te Wā o te Kaha
1. Ringa rīpene
Arotakehia tētahi mea e hurihuri ana, pērā i te tatau o tētahi rūma. Ina whakatuwheratia, ina kati rānei te tatau, ka hurihuri te tatau. Ko ngā inihi e hono ana i te tatau ki te pakitara te tuaka hurihuri.
Ka kitea te ahua o te tatau mai i runga. Arotakehia tētahi tauira i panaia ai te tatau e ngā kaha e rua e rite ana te rahi me te ahunga, ko te ahunga o te kaha he poutū ki te tatau. I te tuatahi, ka panaia te tatau ki te kaha o F.1, r1 mai i te tuaka hurihuri. Muri iho, ka panaia te tatau ki te kaha o F2, r2 atu i te tuaka hurihuri. Ahakoa te rahi me te ahunga o te kaha F1 =F2, te kaha o F2 ka tere ake te hurihuri o te tatau i te kaha o F1. Arā, ko te kaha o F2 ka nui ake te whakaterenga koki i te kaha o F1Ka taea e koe te whakaatu i tēnei.
Kāore te kaha anake e pāngia ana e te kaha, engari e te tawhiti i waenga i ngā pūwāhi mahi o te kaha me te tuaka hurihuri (r). Mena he poutū te ahunga o te kaha ki te mata o te mea pērā i te tauira i runga ake nei, ko te ringa rīwhi (l) he ōrite ki te tawhiti i waenga i ngā pūwāhi mahi me te tuaka hurihuri (r). He aha mēnā kāore te ahunga o te kaha e poutū ki te mata o te mea?
Arotakehia ētahi atu tauira e rua, e whakaaturia ana i te pikitia kei te taha. Ahakoa he rite te rahi o te kaha, he rerekē te ahunga o te kaha, nō reira he rerekē anō hoki te ringa rīwhi (l). I te Pikitia 3, ka ōrite te ahunga o te rārangi mahi kaha ki te tuaka hurihuri kia kore ai te ringa rīwhi. Ka mōhiotia te ringa rīwhi mā te whakaahua i te rārangi mai i te tuaka hurihuri ki te rārangi o te hunga mahi. Me poutū te rārangi o te tuaka hurihuri, me hanga rānei he koki 90o me te rārangi kaha.
Mātakitakihia te ahua 2 kia mārama ake ai koe ki te whārite o te ringa rīwhi.
Sin θ = l / r
l = r sin θ
l = te ringa rīwhi, r = te tawhiti o te pūwāhi o te mahi ki te tuaka hurihuri.
Ko te whārite i runga ake nei hei tatau i te ringa rīwhi. Mena he poutū a F ki a r, ko te koki i hangaia he 90 o.
l = r sin 90 o = r (1)
l = r
Ki te ōrite a F ki a r, ko te koki i hangaia ko 0 o.
l = r sin 0 o = r (0)
l = 0
2.2 Te kaha o te wā (taipana)
2.2.1 Te rahi o te wā o te kaha
I roto i te pāngarau, ko te rahi o te kaha nekehanga te hua o te whakarea o te kaha (F) me te ringa rīwhi (l).
τ = Fl
τ = te nekehanga o te kaha (mita Newton), F = te kaha ( Newton ), l = te ringa rīwhi (mita)
Ka whakamahia te whārite 2 hei tatau i te rahi o te au o te kaha. He rite tonu te pūnaha ā-ao mō te taipana ki te mahi, engari ehara te taipana i te pūngao, nō reira kāore e hiahiatia te whakakapi i te waeine ki te Joule. He maha ngā wā ka whakamahia e ngā tohunga ahupūngao te kupu taipana, engari ka whakamahia e ngā miihini te kupu au o te kaha.
2.2.2 Te ahunga o te au o te kaha
He rahinga whārite te kaha o te wā, nā te mea, haunga tōna rahi, he ahunga anō hoki tōna. Mā te ture ringa-matau ka taea te mōhio ki te ahunga o te kaha. Hurihia ngā maihao e whā o tō ringa matau, me te pupuri tonu i te koromatua o te ringa matau. Ko te ahunga o ngā maihao e whā ko te ahunga o te hurihanga o te mea, ko te ahunga e whakaaturia ana e te koromatua ko te ahunga o te kaha o te wā.
Mena kei runga te ahunga o te nekehanga o te kaha (i te ahunga o te tuaka-y) kei te taha matau rānei (i te ahunga o te tuaka-x), he pai te nekehanga o te kaha. I tetahi atu taha, ki te mea kei raro te ahunga o te nekehanga o te kaha (i te ahunga o te tuaka-y) kei te taha maui rānei (i te ahunga o te tuaka-x), he kino te nekehanga o te kaha. Arā, ki te mea kei te taha matau te ahunga o te hurihanga o ngā mea, he kino te nekehanga o te kaha. I tetahi atu taha, ki te mea kei te ritenga kē te ahunga o te hurihanga o ngā mea i te hurihanga matau, he pai te nekehanga o te kaha.
2.2.3 Ngā tauira raruraru o te wā o te kaha
Ngā tauira raruraru 1.
E 8 mita te roa o tētahi poraka. E toru ngā kaha e mahi ana i runga i te kurupae, pērā i te ahua. He aha te rahi o te nekehanga kaha e huri ai te kurupae i tōna pokapū?
Rongoā:
Kei waenganui te pokapū o te kurupae. E 8 mita te roa o te kurupae, nō reira e 4 mita te tawhiti o te pokapū o te kurupae mai i te pito o te kurupae.
Taipana 1 = F 1 l 1 = (10 N)(4 m) = 40 N m
He pai te taipana 1 nā te mea ka meinga ngā hihi e te taipana 1 kia huri ki te taha whakararo o te matau.
Taipana 2 = F 2 l 2 = (10 N)(2 m) = – 20 N m
He kino te taipana 2 nā te mea ka meinga te hihi e te taipana 2 kia huri ki te taha matau.
Taipana 3 = F 3 l 3 = (15 N)(2 m) = – 30 N m
He kino te taipana 3 nā te mea ka meinga te hihi e te taipana 3 kia huri ki te taha matau.
Taipana kupenga = 40 N m – 20 N m – 30 N m = – 10 N m
He kino te taipana e puta mai ana, e tohu ana tēnei ko te ahunga o te hurihanga o te kurupae he huri ki te taha matau.
Ngā tauira raruraru 2.
F 1 = 10 N, F 2 = 15 N, F 3 = 15 N me F 4 = 10 N, mahihia te tokotoko o te ABCD e whakaaturia ana i te pikitia. Ko te roa o te tokotoko ABCD he 20 mita. Ki te kore e arohia te papatipu tokotoko, ko te tuaka hurihuri kei te pūwāhi D ka whakatau i te rahi o te nekehanga kaha.
Rongoā:
Ko te pātai o tēnei uauatanga, he aha te taipana kupenga e meinga ai te kurupae kia hurihuri, kei te pūwāhi D te tuaka hurihuri.
Taipana 1 = F 1 l 1 = (10 N)(15 m) = 150 N m
He pai te taipana 1 nā te mea ka huri te hihi i te taipana 1.
ki te ritenga kē atu i te ahunga o te matau.
Taipana 2 = F 2 l 2 = (15 N)(5 m) = -75 N m
He kino te taipana 2 nā te mea ka meinga te hihi e te taipana 2 kia huri i te taha matau.
Taipana 3 = F 3 l 3 = (15 N)(0 m) = 0 N m
Kore te taipana 3 nā te mea e ōrite ana a F 3 ki te tuaka hurihuri.
Taipana 4 = F 4 l 4 = (10 N)(5 m) = 50 N m
He pai te taipana 4 nā te mea ka meinga te hihi e te taipana 4 kia huri i ngā taha rerekē ki te taha matau.
Taipana kupenga = 150 N m – 75 N m + 50 N m = 125 N m
He pai te taipana kupenga, nō reira ko te ahunga hurihanga o te kurupae he ritenga ke ki te ahunga hurihanga matau.
