The Mystery of the Self-sealing Sandwich Bag

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!

10 Responses to “The Mystery of the Self-sealing Sandwich Bag”

  1. That is really cool. We’ve read about it, but we’ve never done it. I wonder if there’s a science experiment in there somewhere? *sigh*

  2. I remember doing this with my older kids. Time files and I forgot all about this. However, Rachel “invents” these kinds of experiments all the time so I rarely have to “teach” science experiments to her. I’m sure up in her room somewhere there is a bag of water with a pencil sticking out and a clock to measure the time lapse. She’s a funny one. (Oh and she would surely know the scientific properties involved that interest me almost zero — a chip off Dad’s block.)
    thanks for coming by my blog to say “Hi.” So nice to meet you. See you again soon. : D

  3. Sarah says:

    That is so cool!!

  4. That is soo cool!! My five year old would be thrilled if I do that trick at home!!