In a recent post on Go Ask Mom I demonstrated how to push pencils through a plastic bag full of water – and in the next post I show you how to thread a needle through a balloon. Check out these posts to see exactly how to perform these simple tricks.
Both of these “tricks” are based on the same science principle: Polymers!
Polymers are simply long chains of many (poly) molecules (mers) that have been connected or cross linked together. Many common materials are made of polymers – rubber balloons, plastic bags, nylon pantyhose, even paper (more on that later).
In the “Pencil through the Bag” trick, sharpened pencils are pushed into a plastic bag mostly filled with water. (This is most dramatic when done while holding the bag over someone’s head.) The pencils simply slide between the polymer chains whose cross links hold them together around the hole created by the pencil.
This is exactly what happens when threading a needle through a balloon. However, you need to be careful to pus the needle (or bamboo skewer) through the rubber polymer where it is the least stretched out – near the knot and at the dimple near the top. If you were were to push the needle through the sides, the cross links of the polymer chains may not be able to hold the balloon together and…. POP!
Bonus Polymer Activity: Paper Tearing Contest
Recruit two unsuspecting victims volunteers. Instruct them both to tear a piece of newspaper in half with the straightest tear. However one will tear the paper long ways and the other will tear short ways and they both must tear the paper with a single, uninterrupted tear. Give them each 3 tries to to get their straightest tear.
You can even collect bets if you’re the gambling type. The volunteer tearing longways will always be the straightest as the newspaper is made of polymer-like paper fibers polymers that run lengthwise on the paper. When you tear this direction you are just separating two straight chains of polymers. If you tear short ways, your tear will always make a right-angle turn so that it too lines up with the polymers. Try it!
