Archive for February 21st, 2009

The Mystery of the Self-sealing Sandwich Bag

Saturday, February 21st, 2009

PhotoStory Friday
Hosted by Cecily and MamaGeek


Our twelve-year old son is learning about molecular structures in his seventh-grade science class. I should be asking him about this experiment before posting, but he is out sailing with his dad right now, so I’ll have to try to remember what he said. (Though it’s Saturday morning, I’m posting this as a Photostory Friday.)

Here’s what you do.

First of all, fill a sealable plastic sandwich bag with water.

Next, poke a sharpened pencil quickly through the bag.

The puncture should pull tightly around the holes, preventing any leaking. We left this bag for hours, and it still had not leaked.

Can you guess the reason for this? As I recall, it has something to do with how long the molecular chains are for polymers (plastics). Since the long molecular chain is bound strongly together, it sort of tightens up around the hole.

When our son gets home, I’ll have him take a look at this post to see if I’ve remembered correctly.

See if this works for you!