Is it possible... a leak-proof bag

Science is fun!

It's true. A plastic ziplock bag, water, and a few pencils had her wondering if I would really permit her to spill water all over the house? 

This idea had her both curious and concerned. We opted to perform our experiment in a water-safe location (aka over the bathroom sink). However, our experiment ended up going right over our heads... literally... when we held the pencil-poked bag above each of our heads... just because we could.

Be Your Own Scientist...

Materials:

• plastic ziplock bag
• sharpened pencil(s)
• water
• science journal (optional)

Procedure:

1. Predict what will happen if pencil is pushed into a sealed bag of water in journal.
2. Fill ziplock bag around 3/4 way full with water and seal it shut.
3. Hold the water bag with one hand and use the other hand to firmly push the sharpened pencil into the bag (lower part of bag with water).
4. Observe what happened in journal. Then predict what will happen if pencil is pushed all the way through the bag in journal.
5. Push pencil through the other side of the bag. Continue pushing until the pencil is completely through the other side of the bag.
6. Observe what happened in journal.
7. Push additional sharp pencils in water bag to see what happens (and for fun).
8. Take one pencil out of bag (over sink) and observe what happens. Place pencil back in same hole and observe what happens.

What just happened?

The ziplock bag is generally made of polymer, which happens to be made of long chains of molecules that just happen to be flexible. Those flexible molecules help form a seal around the pencil when it is pushed into the water-filled bag. Hence, the water stays in the bag (no leaks!). However, when the pencil is removed the water leaks out because the molecules were pushed aside leaving a permanent hole in the bag. Hence, the water leaks out of the bag (oh no!).

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