The Science of Polymers — The Leak Proof Bag

Here’s an easy and inexpensive way to get kids excited about science. All you need is a few pencils or cooking skewers, water and some plastic bags. This experiment is perfect for early childhood learners, preschoolers or even older children with a little adult supervision. Sharp pencils and skewers can also poke holes in your skin.

This is a good experiment to do outside, over a sink or tub to catch the drips. Fill the plastic zipper-lock bag with water more than half full. Don’t use sandwich bags or you will get wet. Seal the bag and then take your pencils or skewers and carefully poke them through the bag and through the water, out to the other side.

Are you getting soaked? You shouldn’t be. There may be a few leaks and drips, but the bag should seal itself around the pencil and keep the water from spilling.

How does this work? The plastic bag is made of polymers. Polymers are long chains of molecules. When you poke through the plastic, you are stabbing between the long strands of polymers and the bag seals itself around the pencil keeping the water inside. Just watch out when you remove the pencils. Shower time!

5 replies
  1. Laura Brandwein
    Laura Brandwein says:

    it worked when i did it but i think i put in to much water but it was because i put in a lot of pencils


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  1. […] this experiment is too cool to pass up. Fill a plastic zipper-lock baggie with water and watch how polymers prevent leaking when you poke them with pencils. (Use caution, people—we don’t want to poke little hands!) Even […]

  2. […] The Science of Polymers – The Leak-Proof Bag […]

  3. […] The Science of Polymers – The Leak-Proof Bag […]

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