No has the American O /oʊ/, which is a diphthong. That means we start on one vowel sound and slide to another. In this case, we slide from o to ʊ. Basically we start with very rounded lips and then relax them a bit and close our jaw, raising our tongue
For most people, just holding the “o” longer is enough to achieve the right sound.
Not has the vowel /ɑ/, which isn’t rounded and needs to be made with the jaw fairly open, and the tongue down and back.
In connected speech, Americans use a stopped t on not, making the t without releasing the air.
It’s okay to use a t sound, but to get that typical American sound you need the stopped t. Be careful not to drop the t off entirely, though.
Use no before a noun when you’re not using an article (a or the).
There is no mail.
We have no time.
You also use no before an adjective and noun:
There’s no good time for it.
We have no real issues with it.
We don’t use no before the words any, much, many, or enough.
Use not before nouns when you’re using an article (a or the) with the noun.
That’s not a good idea.
That’s not the right flight.
We use not before the words any, much, many, or enough.
There’s not any reason for it.
There’s not much left.
Not many people know that.
There’s not enough time left.
Use not to make a verb negative:
We could not do it.
They have not called.
For most verbs with not, Americans will use a contraction. Could not becomes couldn’t,
have not becomes haven’t.
We couldn’t do it.
They haven’t called.
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