Leak proof bag experiment

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This leak proof bag experiment is a fun science experiment in which your kids get to poke pencils right through a plastic baggy filled with water.



  • Sharpened Pencil
  • Water
  • Zip-up Bag



  1. Fill a zip-up bag about ½ way with water and sealed up.
  2. Quickly stab a sharpened pencil through the zip-up bag.
  3. Try stabbing multiple pencils through the zip-up bag.


Plastic bags are made from polymers (long chains of molecules) that are flexible. When you stab a pencil through the bag, the polymers move apart but then the flexibility of the polymers push back toward the pencil and form a temporary seal. This prevents the water from leaking out the holes.

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