Phonetics is the study of pronunciation and vocal sounds used in human communication. The main organs of speech are the tongue, lips, vocal cords, palate, windpipe, and teeth. There are 20 vowels in English, including 12 pure vowels and 8 diphthongs. Vowels are classified as short or long. Consonants are non-vowel sounds that involve audible friction or obstruction in the mouth, and there are 24 consonants in English including gliding consonants. Consonants are classified into six types: plosive, fricative, nasal, lateral, affricate, and trill.