First it is necessary for us to have a closer look at the way

Rounding
Vowels may also be different from each other with respect to rounding. If 
you compare /i:/ in /
tʃi:z]/(cheese) with /u:/ in /tʃu:z/ (choose), you will see 
that not only is /i:/ a front vowel and /u:/ a back vowel, but /i:/ is also 
unrounded where /u:/ is rounded. When pronouncing /u:/ your lips are 
rounded, but when pronouncing /i:/ the corners of the mouth are much
further apart.
/i/
/e/
/æ/
/u:/
/ɔ:/
/ɒ/
/
a:/
Lips 
Spread
Close
Lip-rounding
Open
Lip-rounding
Neutrally
Open

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We can summarize the description of English 
vowels in the following explanation. However, 
it is very important to accompany this chapter 
simultaneously with what we learned about 
tongue position. Remember that, as usual, we 
are talking about sounds, not letters, and the 
description belongs to how they are expected 
to be produced.

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Long high front unrounded monophthong

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Short high front unrounded monophthong

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Short mid front unrounded monophthong

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Short low front unrounded monophthong

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Short low central unrounded monophthong

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Long low back unrounded monophthong

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Short low back rounded monophthong

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