Inge and Magne mingle with Bernoulli and use howling tubes to show how the air pressure drops when the air moves.
You need:
- A plastic pipe with grooves
- A cut-off 20 mm pull tube for electrical wires, of approx. 1 meter
- A cup of scraps of paper from a hole punch.
Recipe:
1. Hold one end of the tube and twist the tube quickly. Then you hear a howling sound. The faster you spin it around, the louder the sound. If you spin slowly, there will be no sound.
2. Empty a hole punch or use confetti. Put the paper in a cup. Insert one end of the hose into the cup, and quickly twist the other end around. The pieces of paper will be sucked up through the tube and spread almost like confetti.
The sound occurs because the air inside the tube drawn out when you spin it around. According to Bernoulli's principle, the air pressure drops when the air moves. Bernoulli's equation shows that as the velocity of a fluid (gas or liquid) increases, the pressure will decrease. This principle can also be used, for example, to explain why planes stay in the air, that there is a sound when we talk or that doors suddenly slam.
