La̍t, chiàu bu̍t-lí ê ha̍k-būn, sī ū hoat tō͘ hō͘ mi̍h-kiāⁿ kái-piàn sok-tō͘ (velocity), hêng-thé, ā sī liû-thé ap-le̍k ê chi̍t káng chok-iōng. Kok-chè Tan-ūi Hē-thóng siat la̍t ēng newton (N) chò tan-ūi. It-poaⁿ tī bu̍t-lí ê kì-hō ēng F tāi-piáu la̍t.