Give the definition to the word "Phonetics"?

How are vowels divided According to the position of the bulk of the tongue?

According to the position of the bulk of the tongue vowels are divided into 5 groups:

1. 
   front [ɪ:], [e], [æ] and the nucleus of [eə]
   
2. 
   front – retracted [ɪ] and the nuclei of the diphthongs [aɪ] and [au]
   
3. 
   central [ʌ], [ə:], [ə] and the nucleus of [əu]
   
4. 
   back [ɔI], [ɔ:], [u:] and the nucleus of the diphthong [ɔɪ]
   
5. 
   back – advanced [ɑ:], [u]
   

How are vowels divided According to the height of the raised part of the tongue?

According to the height of the raised part of the tongue vowels are divided into 3 groups:

(A) Close or High [ɪ:], [ɪ], [u:], [u]

(B) Open or Low [æ], [ɑ:], [ɔ], [ʌ], and the nucleus of [aɪ], [au]

(C) Mid – Open or Mid [e], [ə:], [ə], [ɔ:] and the nucleus of [eə], [əu]