What's up? versus What is up?

[Tom]

Hi

Could you please tell me if both are correct?

1-What's up? 2-What is up?

If only the first one is correct, are there some other expressions which can only be used in contraction form?

Tom

[Pamela]

Hi Tom,
Expressions What's up? and What is up? are the same The difference is in contraction, as you know

[Jamie (K)]

Both are right, but people would rarely ask, "What is up?" since in ordinary speech we use contractions wherever possible.