A zipper demonstrates several simple machines working together. The zipper teeth act as wedges (inclined planes), while the zipper pull functions as a lever. The interlocking action of the wedges secures the zipper closed, and the lever provides the force to open or close it.

1. Show students a zipper and use a magnifying glass to highlight the teeth.
2. Explain that each tooth is formed from two inclined planes, creating a wedge.
3. Demonstrate how the wedges interlock to hold the zipper shut.
4. Point out the zipper pull and explain that it acts as a lever.
5. Show how moving the pull applies effort to the lever, which forces the wedge-shaped teeth together or apart.
6. (Optional) Discuss how the spiral design of some zipper teeth resembles a screw, and compare with an actual screw.
7. Draw a diagram on paper or a whiteboard to summarize the wedge, lever, and screw actions.

• None available

• Compare different zipper types (metal vs. plastic teeth).
• Take apart a zipper to let students examine the individual teeth.

• Avoid pulling the zipper too hard, which may break it or pinch fingers.
• Supervise if small parts of the zipper are detached, as they may pose a choking hazard.

• How do the wedge-shaped teeth keep the zipper closed? (The inclined planes force the teeth into interlocking positions, resisting pulling apart.)
• Why is the zipper pull necessary instead of just pushing the teeth together by hand? (The lever allows applied force to be directed evenly across the wedges.)
• How is the zipper similar to other simple machines like ramps or screws? (It uses inclined planes to spread force over distance, reducing effort.)