Paper Bridge STEM Challenge

Understanding Paper Bridge STEM Challenge

A bridge fails when the forces inside it become greater than its parts can handle. Coins push downward because of gravity. The bridge pushes upward at its supports.

Between those points, the paper must carry the force along a path. A flat strip tends to sag in the middle. Its top surface is squeezed, which is called compression.

Its bottom surface is pulled apart, which is called tension. Paper can resist some pulling and squeezing, but it bends easily when it is spread out in a thin sheet.

Changing the paper into a beam gives it more depth. That depth helps the beam resist bending because more paper is placed away from the middle where bending is weakest.

The location of the load matters as much as the total number of coins. A coin placed at the center usually causes the greatest bend because the center is farthest from both supports. Coins placed close to the ends send much of their weight directly into the books or blocks holding the bridge.

During testing, add coins one at a time and watch closely. Notice whether the bridge starts to curve, twist sideways, crease, or slide off its supports.

These are useful warning signs. A sudden collapse often begins with a small weak spot, such as a crushed fold, loose tape, or uneven support.

Engineers use shapes that guide forces into strong parts. In a truss, straight pieces form triangles. A triangle keeps its shape better than a four sided frame, which can change into a slanted shape unless it has extra bracing.

Some truss pieces are squeezed while others are pulled. An arch works differently. It carries much of the load by squeezing along its curve and pushing outward at each end.

This means the supports must be firm. If they can move apart, the arch may flatten. Students see the same force ideas in playground climbing frames, roof beams, bicycle frames, cardboard packaging, and shelves that bend under heavy books.

A fair test changes one design feature at a time. Start with one basic bridge and record how many coins it holds. Then make a new version with one planned change, such as a different fold, an added center support, wider ends, or stronger joints.

Keep the gap width, paper size, coin type, and placement method the same. This helps show which change caused the result. A design that holds fewer coins is not wasted work.

It gives evidence about what did not help and why. Good engineers use failure to improve the next model. Clear notes, simple sketches, and careful observations matter because they turn a craft activity into an engineering investigation.