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1. Crease in half
Lay the A4 sheet sideways, coloured side up. Fold the bottom long edge up to the top long edge and unfold.
2. Crease into quarters
Fold the bottom edge up to the middle crease and unfold. Fold the top edge down to the middle crease and unfold. There are now 3 creases.
3. Crease into eighths
Fold the bottom edge up to the first crease and unfold, then up to the third crease and unfold. Do the same from the top edge. Now there are 7 creases and 8 strips.
4. Crease into sixteenths
Fold the bottom edge up to the 1st, 3rd, 5th and 7th creases in turn, unfolding each time. Do the same from the top edge. You get 15 evenly spaced creases (about 1.3 cm apart on A4).
5. Pleat it like a fan
Starting from the bottom, fold the creases valley, mountain, valley, mountain… in turn, so the sheet pleats up like a fan. Press every pleat firmly.
6. Open the pleats a little
Spread the fan a little until every pleat is at about a right angle. Seen from the end it is a zigzag. That is your paper bridge!
1. Crease in half
Lay the A4 sheet sideways, coloured side up. Fold the bottom long edge up to the top long edge and unfold.
Tip:
Finished!
Well done! Watch it again or try another model.
Try the science
- First lay a flat, unfolded sheet across two cups. Put coins in the middle one by one; it soon sags and drops. Write down how many coins it took.
- Now lay the pleated bridge across the same cups, pleats running from cup to cup, and add the same coins one at a time along the pleats. Count how many it holds and compare.
- Fair test: use the same paper, the same gap between the cups and the same coins, try each bridge three times and compare. Then try wider or narrower pleats, or open the fan more or less.
- Why is it stronger? Pleating stands parts of the paper on edge, so the same sheet bends much less. The wavy layer inside cardboard boxes and corrugated metal roofs work the same way.