# Learning Lesson: Going with the Flow

### Overview

Bernoulli's principle states that in fluid flow (which includes air), as the velocity of a fluid increases, its pressure decreases. The students will discover that the faster air moves, the lower the pressure becomes within that flow of air. They will see this effect by blowing between two soda cans.

TOTAL TIME 5 minutes Two (2) empty soda cans, a level surface None None Tornado safety

### Procedure

1. Lay the two cans on their sides parallel to each other, about one inch apart, near the edge of a level surface.
2. Ask the students to predict what will happen when air is blown between the cans: Will the cans move apart or together? Have them explain why they made their prediction.
3. Put your face down near the surface and blow lengthwise between the two cans.
4. It will take some trial and error, but eventually the two cans will roll together.
5. Another way to demonstrate is by suspending two cans on string about an inch apart and have the student blow between them.

### Discussion

Students may expect the cans to move apart as air is blown between them, however, the opposite occurs. This effect is Bernoulli's principle in action, named after the eighteenth-century Swiss mathematician and physicist Daniel Bernoulli. He discovered that the faster a fluid moves, the lower its pressure becomes. Because air is a fluid, this principle is important in understanding wind and weather conditions. It also has applications in aviation and airplane flight because it explains how planes generate lift as they increase in speed.

By blowing between the two cans, the air between them moves faster than the surrounding air, lowering the pressure between the cans. The cans roll together as the higher pressure surrounding the two cans (away from the air flow) pushes the cans together toward the region of lower pressure.