Puncture Proof Kit
PUNCTURE PROOF EXPERIMENT
Experiment Procedure
- Fill one zipper-lock bag about ½ to ¾ full of water and seal tightly. Hold it over a tub (if you need it, otherwise you can be a daredevil and hope that nothing spills).
- Hold the zipper part of the bag with one hand and a pencil in the other. Slowly but firmly push the pencil through one side of the bag. You don’t need to jab it through very quickly, just make sure you push it through with a fair amount of pressure. Note: Be careful that your hand isn’t in the way on the other side! Also, don’t wiggle around the pencil at all, or else the bag will stretch out and leak. When removing the pencils, be prepared for a mess!
- Blow up a balloon knot the end.
- Rub the point of one of the skewers to sharpen it.
- Gently twist the skewer into the balloon right next to the not.
- Push the skewer through the top end of the balloon.
Materials List
- Wood Skewer
- Clear Balloons
- Sandpaper
- Sharpened Pencils
- Plastic zipper lock bag (make sure they are zipper lock; the ones with the fold top are not thick enough)
- Water
- Adult Supervision
How Does It Work?
Despite what it looks like, the zipper-lock bag isn’t covered in a magical sealant that blocks leaks. Well… not exactly. Plastic bags like these are made out of our favorite kind of materials, polymers! Polymers are long chains of individual molecules, called monomers. (See that? Mono = one. Poly = many. Mers = molecules.) When you puncture these bags with a sharpened pencil, you’re essentially separating polymer chains without breaking them. The long chains of molecules in the thicker, zipper lock bag squeeze in tight around the surface of the pencil preventing any sort of leak. The grocery bag, on the other hand, is made of thinner plastic that can be stretched more easily and will not rebound back to its original shape. The weight of the pencils also pushes down on the thinner plastic, creating larger holes that the water leaks out of. Polymers continue to prove an indispensable part of life.
If you could see the latex that makes up a balloon on a microscopic level, you would see many long strands of molecules. The elasticity of these strands (called polymers) causes latex to stretch.
The secret is to uncover the portion of the balloon where the latex molecules are stretching the least. After drawing on the balloon with the Sharpie marker, you probably noticed that the dots on either end of the balloon were relatively small. You’ve just uncovered the area of least stress… the ends of the balloon. The two ends are where the latex is the least stressed, and the long molecules stretch AROUND the skewer and keep the air inside the balloon from rushing out. It’s easy to accidentally tear the rubber if you use a dull skewer or forget to coat the end of the skewer with vegetable oil. When you remove the skewer, you feel the air leaking out through the holes where the polymer strands were pushed apart. Eventually the balloon deflates… but it never pops. You can try to pierce the balloon through the middle, but just know you’ll be going out with a bang!
TAKE IT FURTHER!
Experiment Procedure
- Try the same thing you did with the zipper lock bag and the pencils using the thin produce bag you can find at the store.
Materials List
- Thin produce bags from the grocery store
- Water
- Tub, bucket, or bowl to catch dripping water
- Pencils (sharpened)
- Paper towels
- Adult Supervision
