ˈæɹɪstˌɑːɾəl dᵻskɹˈaɪbz tˈuː kˈaɪndz ʌv mˈoʊʃən: "vˈaɪələnt" ɔːɹ "ʌnnˈætʃɚɹəl mˈoʊʃən", sˈʌtʃ ɐz ðæt əvə θɹˈoʊn stˈoʊn, ɪnðə fˈɪzɪks tˈuːhˈʌndɹɪd fˈɪfti fˈoːɹ bˈiː tˈɛn, ænd "nˈætʃɚɹəl mˈoʊʃən", sˈʌtʃ ɐz əvə fˈɔːlɪŋ ˈɑːbdʒɛkt, ɪn ɔnðə hˈɛvənz θɹˈiːhˈʌndɹɪd ˈeɪ twˈɛnti.
Aristotle describes two kinds of motion: "violent" or "unnatural motion", such as that of a thrown stone, in the Physics (254b10), and "natural motion", such as of a falling object, in On the Heavens (300a20).