How do arches work? Explore compression, tension, equilibrium, and more in this Fun with Arches video by G. Wayne Brodland, professor of engineering at the University of Waterloo in Ontario, Canada. In this series of demonstrations, he explains how an arch gets its strength, revealing the vertical and horizontal forces that are transferred down into the arch’s base.

He also demonstrates how a chain suspended from both ends can reflect a successful arch. Dandi Zhao and Zi Yang assist. Via Wikipedia:

Architecturally, a catenary arch has the ability to withstand the weight of the material from which it is constructed, without collapsing. For an arch of uniform density and thickness, supporting only its own weight, the catenary is the ideal curve.

Catenary arches are strong because they redirect the vertical force of gravity into compression forces pressing along the arch’s curve. In a uniformly loaded catenary arch, the line of thrust runs through its center.

Brodland has a series of video lessons, activities, and downloadables on his Mechanical Models site that can be used for class or at home, including the arches activity above. Though his videos proceed methodically, he encourages learners to take their time, and to have fun exploring and testing how “the forces in an arch interact for equilibrium to exist.”