demonstrations:pencils_through_bag
Pencils Through a Bag
Materials: ★☆☆ Easy to get from supermarket or hardware store
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★☆☆ Minimal safety procedures required
Categories: Materials, Polymers
Alternative titles:
Summary
When pencils are pushed through a water-filled plastic bag, no water leaks out.
Procedure
- Fill a resealable plastic bag about two-thirds full of water and seal it tightly.
- Hold the bag over a sink, bucket, or outdoors to avoid spills.
- Carefully push a sharpened pencil straight through one side of the bag and out the other side.
- Try with additional pencils to see how many can be pushed through without leaking.
Links
The Pencils Through a Bag Experiment - We Are Teachers:
Science Behind A Pencil Thru a Bag Full of Water (No Spills!) - SD Lab Rats:
📄 Poke but don't Soak - ACS: https://www.acs.org/education/whatischemistry/adventures-in-chemistry/experiments/poke-dont-soak.html
Variations
- Use colored water in the bag to make leaks easier to see.
- Experiment with other sharp objects (toothpicks, knitting needles) to compare results.
- Measure how many pencils can be pushed through before the bag eventually leaks.
Safety Precautions
- Adult supervision required - pencils and skewers are sharp.
- Perform over a bucket, sink, or outdoors to contain spills.
Questions to Consider
- Why doesn’t water leak out of the bag even when pencils poke through it?
- What property of polymers allows the bag and balloon to stretch and reseal around the objects?
- How is the material of the bag different from stiff materials like glass or wood?
- Where in everyday life do we rely on flexible, sealing materials like this?