Materials Required:
l Cellophane packaging material
Procedure:
- Save the plastic wrapper from a packaged food item, such as a bag of pretzels.
- Try to make a rip in the cellophane by poking your fingers into it, then pulling it apart. You will find that it is very hard to start a tear, but it is easy to keep it going after it has started.
This Is What Happens:
When you pull against opposite ends of the plastic, your force is spread over a large area. The plastic may stretch, so starting a tear is very hard. Once a tear has begun, however, most of the stress is concentrated at this single point, and you do not have to pull very hard to continue the tear.
