Exploding Straws
Perhaps the word “exploding” is a bit too strong.

Concepts
air pressure, compressibility of air, inferences

Materials
Drinking straw

Procedure
Initially students can make observations of the drinking straw. In particular, how difficult is it to push the straw together. Discuss with the students if there is anything inside the straw.

Now put the students in pairs and have one of them 1) grasp the drinking straw at both ends, 2) pinch the opposite ends of the straw firmly, 3) wrap the ends of the straw tightly around their fingers until they get a small pocket of air in the middle of the straw, and 4) have the other student flick the straw with their finger to make it pop.

Results
Have students describe the straw before and after it was wrapped around one of their fingers. Additionally, have them do their best to explain why the straw pops.

Explanation
Winding the straw compresses the air inside of it; eventually creating a pocket in the center where the air pressure is greater on the inside of the straw compared to the air pressure outside of the straw. Flicking the straw separates the long molecules that compose the plastic and allows the pressurized air on the inside to rapidly escape, causing a popping sound and splitting the straw in the process.

figure36.jpg
Figure 36: Wind the straw and have a friend flick it in the middle. Pop!

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