Apparently, this application of Boyle’s Law of pressure and volume has been around for 50 years, but I’ve only recently seen it.
Materials:
• Plastic straw
• Another individual
CAUTION: Loud noises can sometimes be scary. Warn others around you that there may be a loud sound.
Experiment:
Pinch the ends of a straw and holding the straw vertically, start twisting the straw by moving your hands like you’re cranking the pedals of a bike. The straw will start shrinking in size. Once you have the straw to about an inch in length, have the other individual give the middle part of the straw a “thwack” with their finger (it may need to have multiple hits or harder hits). It is a successful demonstration if you hear the popping sound.
What’s happening?
Our understanding of chemistry and how it involved atoms and molecules started to become better understood when we began to understand gases (it took till the 1800s for John Dalton to fully comprehend the experiments). In the 1600’s, Robert Boyle experimented on gases and confirmed the relationship between the volume and pressure of a gas. As the volume decreased, the pressure increased and if the volume increased, then the pressure decreased. This is a rather simple concept once you understand that pressure is produced by these atoms/molecules as evidenced by the graphic here:
Each straw holds the same number of atoms/molecules, but the second one is under greater pressure because they are in a smaller volume.
Extension:
Does the demonstration work better with large or small straws? What happens if you put water in about ¼ of the straw (do this one outside or over a sink)?
References
https://www.youtube.com/watch?v=P5QuZ9uLkkU
To view past “ChemShorts for Kids” activities, go to:
https://chicagoacs.org/ChemShorts.
