Context.
The vowel in new is long, whether it is pronounced noo or nyoo.
It is a short vowel word. The I has a short I sound.
The word "head" has a short vowel sound.
Is the word wanted a long a sound or short a sound
Long A sound
A short 'a'. A long a would be for example in the word 'farm'.
The word "wiper" has a short "i" sound.
The word "basket" has a short a sound.
The word mitt has a short i.
The word "potato" has a short vowel sound for the letter 'a'.
The word "swam" has a short vowel sound. The "a" is pronounced as /æ/ in this word.
The vowel "i" can be both short and long. For example, in the word "sit," the "i" is short, and in the word "fine," the "i" is long.