Material Required:
- Cellophane packaging
material
Procedure:
- Save the plastic wrapper from a packaged food-item.
- 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 make a tear, but it is easy to keep it going after it has started.
This is what happens:
When you pull against the opposite ends of the plastic, your force is spread over a large area. The plastic may stretch; so making 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.
