Students apply enough pressure to "explode" a straw.

When you twist the straw, the same amount of air is being pushed into a smaller and smaller space. This increases the air pressure inside the straw.

The straw isn't strong enough to withstand extra pressure caused by a fingernail flick against the pressurized area. The straw cracks and the air rushes out, flowing from an area of high-pressure to an area of low-pressure.

The sudden release of high pressure in the straw causes the loud pop due to the rush of air. This is the same effect as when a balloon pops.

### Objectives

• Explain how air pressure works.

### Materials

• Per pair of students:
2 plastic drinking straws

### Key Questions

• When the ends of the straw are twisted tightly, what happens to the trapped air inside the straw?
• What triggered the straw to explode?
• What is responsible for the “pop” sound?

### What To Do

1. Get the students into pairs.
2. Tell one student to take a straw and bend each end at a 90° angle to the middle of the straw (so the straw looks like a boxy S-shape).
3. Tightly pinching the bent ends of the straw, the student twists the straw in a pedal motion. As she twists, the amount of straw between her fingers will get smaller.
4. The student twists until she can’t twist anymore. She should have about 2–3 centimetres of hard, untwisted straw between her fingers.
5. The second student can then flick her middle finger at the untwisted portion of the straw with her fingernail. A loud pop will be heard.
6. Get the students to swap roles.

### Extensions

• Predict what will happen if you lengthen or shorten the length of the untwisted part.
• How would you make softer or louder sounds with your straw poppers?

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