How we did it:
- plastic zip bag
- round pencils - with sharp tips!
Fill the plastic bag halfway with water.
Use one hand and hold the plastic bag at the top for stability.
Use a pencil to quickly pierce the bag and water!
What's going on?
Most plastic bags are made of polyethylene, a polymer that is durable, flexible, and shaped like long strands. When the pencil is quickly pierced into the bag of water, the polyethylene molecules separate but don't break, forming a seal around the pencil. If the pencil is pierced into the bag before the water is put in, the water will leak!
Try the experiment with a faceted pencil, a larger pencil, or a thicker plastic bag. What happens?