Te Ture Tuatoru a Newton e kī ana mēnā ka pā te kaha o te mea 1 ki te mea 2, ka pā te kaha o te mea 2 ki te mea 1 i taua wā anō. He rite te rahi o ngā kaha e rua engari he rerekē te ahunga o ngā kaha e rua. Ka kiia tētahi kaha ko te mahi, ka kiia tētahi atu kaha ko te tauhohenga.
Ko te tohu kino e tohu ana i te ahunga o te kaha. He pai te mahi F, ko te tauhohenga F ia he kino. E tohu ana tēnei kei ngā ahunga rerekē ngā kaha mahi me te tauhohenga.
Whakahaerehia he whakamātautau kia pai ake ai te mārama ki te ture tuatoru a Newton. Mena he papa reti tāu, pana ki te pakitara i a koe e tū ana i runga. I muri i tō pana ki te pakitara, ka neke whakamuri te papa reti mai i te pakitara. Ka pana whakamua tō pana, i te mea ka neke whakamuri te papa reti. E whakaatu ana tēnei kei te pana anō hoki te pakitara ki a koe. Ina pana koe ki te pakitara, kei te pana anō hoki te pakitara ki a koe. Ka mahi tō kaha pana ki te pakitara, i te mea ka mahi te kaha pana o te pakitara ki a koe. He ōrite te rahi o ngā kaha e rua engari he rerekē te ahunga. Ka taea e koe te kī ko tētahi kaha he mahi, ko tētahi he tauhohenga.
Ko tētahi atu whakamātautau ka taea te mahi ko te pupuhi i tētahi poihau rapa, ā, i muri i te whakawhanuitanga o te poihau nā te mea kua kī i te hau, ka tukuna te poihau. I muri i te tukunga, ka "rere" te poihau. Ko te ahunga o te nekehanga o te poihau he ritenga kē ki te ahunga o te hau e puta atu ana i te poihau. Me pēhea te whakamārama i tēnei? Ina whakatuwheratia te waha o te poihau, ka panaia te hau e te poihau ki waho, ā, i taua wā anō, ka panaia hoki te poihau e te hau. Mā te pana hau ka rere te poihau. Ka mahi te pana hau ki te poraka, ā, ka mahi te pana o te poihau ki te hau. He rite te kaha o ngā kaha e rua engari he ritenga kē.
Whakaarohia te ahua o tētahi poraka e takoto ana i runga i te papa. Ko te kaha noa e pā ana ki te poraka (N) ko te kaha noa e tukuna ana e te papa ki runga i te poraka. I taua wā anō, ka tukuna hoki e te poraka he kaha noa ki runga i te papa (N'). He ōrite te rahi o ēnei kaha noa e rua (N me N') engari he rerekē te ahunga, ā, ka pā hoki ki ngā mea rerekē. He rerekē tēnei i a N me w e pā ana ki te mea kotahi, arā, ki te poraka. Nō reira, ko N me N' he kaha mahi-tauhohenga.
