What You Need:
- Sharpened pencils
- Zip-lock plastic bags
- Paper towels
- Sharpen your pencils. Fill a zip-lock bag between 1/2 and 3/4-full with water.
- Hold a pencil in one hand and the top of the bag in your other hand. Slowly, but firmly, push the sharpened pencil through one side of the bag. You won't see any water gushing out!
- Push the pencil through the other side of the bag too. Nothing will happen. (Note: Do not push the pencil all the way through either side of the bag. As soon as the end of the pencil gets past the bag, you'll have a big wet mess.)
- You can keep demonstrating this experiment by repeating the act with the other sharpened pencils.
- Once you're finished, hold the bag over a sink and remove the pencils. The water will come pouring out of the holes.
Plastic bags like zip-lock bags are made out of polymers. Polymers are long chains of individual molecules, called monomers ('mono' means 'one', 'poly' means 'many' and 'mers' means 'molecules'). When you puncture these bags with a sharpened pencil, you are essentially separating polymer chains without breaking them. The long chains of molecules then squeeze in tightly around the surface of the pencil, preventing any sort of leak.