"of" seems to be pronounced with the f sound asˈäf in phrases like "of course". But 'of' is pronounced as \əv in a lot of other cases.
Yet, Merriam Websters gives the one with 'v' sound as the only pronunciation.
https://www.merriam-webster.com/dictionary/of
Why is that? Why does the dictionary give the one with 'v' sound as the only pronunciation?
In what cases 'of' is pronounced with f versus pronounced with v sound?