Look at these two bridges. One is a straight flat deck. The other is a stone arch. Which do you think would hold more weight across the same gap, and why?

Today we will bridge the same gap three ways, load each with 1c coins until it fails, and see what the evidence says.

Three shapes can span a gap:

• Beam — straight and flat
• Arch — curved, pushing out at the feet
• Braced beam — straight, with triangles underneath

In your group, bridge the same 15 cm gap three ways with equal card strips.

• Flat beam: one straight strip across the books.
• Arch: one strip curved up in the middle.
• Braced beam: a straight strip with folded card triangles underneath. How to make a brace: fold a short card scrap into a triangle shape, then tape it under the middle of the beam so the point faces down and both sides touch the beam.

Test one span at a time. Stack 1c coins in the middle, one coin at a time, until the span gives way. Count the coins it held. Watch where it fails.

Check your Investigation Journal page has each span type, how many coins it held, and where it failed. That page is your only written record.

Your teacher will type one clear set of coin counts into the interactive activity on the board: one row for beam, one for arch, one for braced beam. Watch the bar chart together. Which bar is tallest?