It's in the Bag!
- Posted on
- By Hema and Eric Bulmer
- Posted in polymers, surface tension, video, water
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!
Purpose
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
Procedure
- Fill the baggie 2/3 full of water
- Squeeze most of the air out of the baggie
- While holding the baggie hanging from one hand...
- Stab the pencil all the way through the baggie
Hints
- Make sure the pencil is sharp and long enough to go all the way through both sides of the baggie
- Try to guide the tip of the pencil in a straight line like a dart - do not tear downward
- 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.
Extensions
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.