Answer:
I run up and down the stairs without moving
From house to house I go, sometimes narrow, sometimes wide. Whether there's rain or snow, I always stay outside. What am I?
I shift around though always slowly. I never move more than a few inches at a time. A large movement by me can kill many people. I am huge yet unseen by humans.
I make things short but I am pretty long myself
I pass before the sun, yet make no shadow. I'm all around you, but you cannot see me. What am I?
Millions of these are crushed every morning to help people wake up.