How is a diphthong characterized in phonetics?

A diphthong is characterized as a combination of two vowel sounds that are pronounced in a single syllable, where the articulation transitions from one vowel quality to another within that syllable. This means that when producing a diphthong, there is a noticeable change in the tongue position and mouth shape as you move from the first vowel sound to the second.

For instance, in English, the sound in the word "coin" starts with an "o" sound and glides towards an "i" sound. This dual character is what distinguishes a diphthong from a simple vowel sound, which has a steady-state quality and does not involve such a transition. Diphthongs are critical in phonetic analysis because they can affect syllable structure and stress patterns in various languages.