Pressure

Bert Says:

You would imagine that by blowing hard down the gap between two papers that they would separate, but the opposite happens!!

The harder you blow the more the papers are drawn firmly together.

Similar events can be witnessed in everyday life, in that a door closes in the draught of a house rather than the door opens.

(Monochrome Photograph Middle Left showing) - When a smooth stream of air flows into a constriction it will speed up and this will decrease its pressure.

(Monochrome Photograph Bottom Left showing) - When the air flows out again, after the constriction, it will slow down before it resumes to its original pressure before entering the constriction.