The way I came to think of it when I studied Latin: V is the consonant version of U, just as J is the consonant version of I.
When you put those vowel sounds next to another vowel (assuming a certain Romance pronunciation similar to modern Spanish or Italian), they tend to make that consonant sound (similar to English W or the consonant version of Y).
When you put those vowel sounds next to another vowel (assuming a certain Romance pronunciation similar to modern Spanish or Italian), they tend to make that consonant sound (similar to English W or the consonant version of Y).