The difference between æ and ɑː in American English

Hi guys. I have been following American Accent for a while and I notice one of the most striking difference between British Accent and American Accent is "ɒ" in British Accent is pronounced "ɑː" in American Accent, such as "stop", "follow"...
But I have 2 problems. Firstly, I don't know what exactly is the difference between "æ" and "ɑː", and I can't find any material online which can help me with this problem. Even materials on how to pronounce "ɑː" correctly is hard to find.
Secondly, when I watch American shows or movies, I still hear people pronounce "ɑː" as "ɒ" in British Accent, for example they pronounce "not" as "nɒt" while the dictionary tells me that this should be pronounced as "nɑːt". So I am quite confused and want to receive some help from you. Thanks in advance.

Daniel Jones made recordings of IPA vowel sounds, though I've not found them on the net anywhere. Besides, while they would be phonetically accurate the phonemes of English have changed since his day. A further complication is that the Am E /æ/ phoneme and the Br Eng /æ/ phoneme may not always be the same as the [æ] as defined by the IPA. Note: in that last sentence, the words 'be the same' make very little sense anyway! ;-)

b

still waiting for someone to confirm this. to be honest, I'm not sure whether I should continue to pronounce /ɒ/ as /ɑː/ or not (

-hell_boy- said:

still waiting for someone to confirm this. to be honest, I'm not sure whether I should continue to pronounce /ɒ/ as /ɑː/ or not (

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If you're pronouncing English the American way, father and not have the same stressed vowel in most places.