Tube Mystery

For this experiment, you will need a 1 1/2″ (4 cm) length of tube (cut off the end of a toilet-paper or paper-toweling tube) and a straw.*

Place the tube on a table, point the straw at the middle of its side, and blow through the straw. The tube rolls away from you, right? Right.

Now aim the straw at an angle downward, just over the tube (see illustration), and blow sharply through the straw. What happened?

No, the tube did not roll back toward you. If you blew sharply enough, it rolled rapidly away from you.

Why? You created a low-pressure area in front of the tube, and the normal air pressure behind it forced it forward. Use of this principle is one thing that helps an airplane fly. Air flowing over its curved top helps give it the “lift” it needs to stay in the air.