It's in the Bag!

It's in the Bag!

Learn about polymers and surface tension with this Hands-On science experiment! All you need is a resealable baggie, a sharp pencil and some water.

It's in the Bag!



To learn about polymers and surface tension with a Hands-On science experiment that will amaze your family and friends!


Materials Needed

  • A resealable (ziplock) baggie
  • A sharp pencil (the longer, the better)
  • Water




  1. Fill the baggie 2/3 full of water
  2. Squeeze most of the air out of the baggie
  3. While holding the baggie hanging from one hand...
  4. Stab the pencil all the way through the baggie



  1. Make sure the pencil is sharp and long enough to go all the way through both sides of the baggie
  2. Try to guide the tip of the pencil in a straight line like a dart - do not tear downward
  3. Practice a few times to line things up and then give is a quick FINAL STAB


What's Going On?

The plastic bag is made up of polymers which are long chains of molecules (imagine a chain of paper clips). When you push the pencil through the plastic these molecules temporarily move aside but then they "snap back" into place forming a tight seal around the pencil and preventing water from leaking out.


In addition, the surface tension of the water plugs up any remaining small holes and prevents further leakage. Imagine a drop of water on a glass surface and think about its rounded shape - this is surface tension and it is one of the things that holds the water together as a droplet. In this experiment the surface tension plugs up the smallest gaps between the baggie and pencil.



Try to insert a second pencil.


Knowing what you do about chains (polymers) what do you think would happen after the 3rd or 4th pencil was poked through the plastic bag?


© Hema and Eric Bulmer. All rights reserved.

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