Demo #7 – Drinking Straw Explosion
Useful in Units: Gas Laws
Background and Uses
This is a fun and easy demonstration showing that as the volume of a sample of gas is decreased at constant temperature, the pressure of the gas increases (Boyle’s Law). I find that very few of the students have ever seen this party trick and they are surprised by the result.
Alterations to try and pitfalls to avoid for this demo:
- Some brands of straws work better than others. Make sure to test the straws ahead of time.
- Make sure to get more than enough straws for your students. This is a trick that can fail when the students first try.
Concepts the Demo Illustrates:
Boyle’s Law, Combined Gas Law, Volume, Pressure
Where I found this demonstration:
My older cousin Mike showed this cool straw trick to me when I was a kid after he got a job at McDonald’s. He learned it from some of the other employees. McDonald’s straws do work really well.
Procedure (Drinking Straw Explosion)
- 2 people
- Student 1: Pinch each end of a drinking straw tightly. Roll the straw end over end so that the straw is winding up and the volume within the straw gets smaller and smaller(see pictures below). Once it is too difficult to roll the straw up any more, continue to pinch tightly and hold the straw steady for Student 2 to flick.
- Student 2: Flick the straw with your finger quickly and with force so that the straw pops.
What to illustrate/discuss with this demo:
- As Student 1 is rolling up the straw, the volume of the gas in the straw is decreasing even though no gas escapes. As the volume decreases and the gas particles get pushed closer together, the pressure (gas collisions per time with walls) increases.