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VOCABULARY:Polymer—a very large molecule made by joining a lot of small units together that are all the same.

Water in a Bag Polymer Experiment

MATERIALS:

• Zip-top bag (must zip closed)• Sharpened pencils• Water• Sink or outdoor space

INSTRUCTIONS:Step 1. Fill your zip-top bag about 2

---3 full of water.

Step 2. Seal your bag shut. Double-check to make certain the bag is sealed.

Step 3. Either go outside to an open space or hold your bag over the sink. Carefully and slowly insert your sharpened pencil into the bag below the water line. Observe what happens.

Step 4. Push the pencil through the other side of the bag and observe again.

Step 5. Try pushing through more pencils.

Step 6. Be careful when removing the pencils because the hole will not reseal itself and water will squirt out.

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THE SCIENCE BEHIND IT:Plastic, zip-top bags are made up of polymers. To get an idea of what a polymer is, look at the long strand of beads below. The single, long strand of beads is made up of many smaller beads attached together, all of which are the same type. That is what a polymer is. It is a very long molecule made up of many smaller molecules bonded together, all of which are the same type.

Think about this: If you were to put that long strand of beads in a cup, do you think you could stick a pencil in the center of it so that the pencil would stay standing? Yes, you could! The reason you could is because when the pencil pushes through the beads, you are pushing between them and they form around the pencil, giving it support so that it will stand.

Pushing a pencil through a plastic, zip-top bag works the same way. Since the bag is made up of polymers, when you pushed the pencil through it, you were pushing in between the smaller units of the polymer. The smaller units around the breakthrough point offered support to the surrounding plastic and it sealed around the pencil, preventing water from leaking out of the bag.