What Am I Riddles

Question: Until I am measured, I am not known. Yet how you miss me, When I have flown What am I?

Question: What force and strength cannot get through, I with a gentle touch can do, And many in the street would stand, Were I not a friend at hand.

Question: I live in the dark, I have no heart and I'm just like jelly, if you touch me I'll stung you. What am I

Question: what does not move outside (the surface)but moves inside ?

Question: I never was. Am always to be. No one ever saw me, nor ever will. And yet I am the confidence of all who live and breathe. What am I ?