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Grades K–2 · Machines

How can a stone arch hold up a bridge?

A stone arch bridge has a curved row of stones. Each stone is wider at one end, a little like a wedge. The stones fit closely together above the open space.

M44 visual explanationThe stones pass a push around the arch. Strong supports at both ends keep it from spreading apart.Stones pass the push around the curveWeightStones pushon stonesStrong supports push backBoth ends need support

In the diagramStones pass the push around the curveWeightStones pushon stonesStrong supports push backBoth ends need support

Weight pushes down. The stones pass the push around the curve. Strong supports at both ends push back.

Weight pushes down on the arch. The stones squeeze against their neighbors. This push passes around the curve and toward both ends of the bridge.

The arch also pushes outward at its ends. Strong supports there push back. They keep the ends from spreading apart. The stones and the end supports work together to hold up the bridge.

About this explanation

Starting knowledge: Recognize a push, weight and a support.

Connect this idea: Structures & Materials

Sources

  • PBS / WGBH — Building Big: Arch Bridge Forces
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