In Lessons 3 and 4, we discovered that the pop-up book always seems to “know” where it “wants” to make the fold. Also, it follows some rules when it does so, such as “it always makes the fold on the far side.” In this lesson, students learn to predict where the fold will come out on the strip. To do so, they measure the four link lengths, discover a mathematical pattern that connects them, and write an equation expressing this pattern.

**For each student:**

- Scissors, tape, Ball-point pen and rulers
- Parallel-fold Template, printed or photocopied onto 8 ½″ x 11″ cardstock
- Worksheet: The Pop-up Computerand
- Science notebooks
- Folder for saving pop-ups

**Inside the mind of the pop-up computer**: Explain that we’ll be doing an experiment to find out where the pop-up book makes the fold. Once we know, we can always make the fold in the right place in advance, and be certain that the book will “respect” the fold we made.**Hinges & links**: Review the four hinges of a pop-up. See a video describing the four hinges. Next, introduce the four links and the lengths of these links.

See a video showing the four links and defining the link lengths: A, B, C & D**Doing the experiment**: Demonstrate how to assemble the pop-ups and measure the four link lengths. Provide time for each student to collect data and record it on the Worksheet.**Analyzing data:**Post data on the blackboard or chart paper. Remove bad data, and help the class look for patterns in the good data. See a video showing how to analyze the data.

**Outcome**: If everything is done correctly, students will discover that A + B = C + D

Data can be invalid due to…

- too much tape
- wrong strip length
- strips not taped perpendicular to the gutter and ruler lines
- measurement errors