On Earth, gravity attracts everything towards the ground. This makes it very easy to figure out which way is up and which way is down.
Gravity is also the reason why mucus (the “runny” part of a runny nose) always comes out of your nose.
Mucus is made up of water, sugars, and proteins. Unlike tap water, mucus is thicker and doesn’t flow as easily. Liquids that don’t flow easily are said to be viscous. White glue, pancake syrup, and motor oil are examples of viscous liquids.
All liquids flow. Liquids poured on a counter top will spread out until it reaches the lowest point or it can’t flow anywhere else. Liquids flow because gravity is constantly attracting all the molecules to the ground.
In space, the rules change. Check out this interesting video that shows an astronaut demonstrating how water behaves in space.
That’s not how water behaves on Earth, but it's really cool!
What’s going on?
Without gravity, the water molecules are no longer being pulled towards the ground. Instead, it seems to just float like the astronauts do.
So, if an astronaut had a runny nose in space, where does the mucus go in the absence of gravity?
Since there is no gravity to pull the mucus out of an astronaut’s nose, I think that a runny nose in space wouldn’t run. In other words, the mucus would probably stay in the astronaut’s nose until it is blown out.
A runny nose is annoying here on Earth, but can you imagine a nose full of mucus that doesn’t run? That would feel very weird!