Umbrella ribs work like a small frame of levers that push the canopy outward when opened.

The longer version

Opening an umbrella pushes a runner up the shaft, and short links convert that straight movement into the swinging of the ribs. Each rib pivots at the top of the shaft and is braced partway along by a stretcher, so pushing the runner outward forces the whole frame to spread into a dome and hold that shape.

The arrangement is a set of four-bar linkages, the same idea used in folding chairs and extending gates. Longer ribs mean more coverage but a longer arm for wind to push against, which is why large models use more ribs and thicker stretchers. Folding versions add extra joints so the ribs can double back on themselves for carrying.

Where this entry sits

Odd Little Things looks at the ordinary objects people touch every day and the small mechanisms and histories hiding inside them. Buttons, zips, pencils, mirrors, stairs, stamps, packaging, and road signs all get their turn. The full list sits on the Odd Little Things page, where every entry is listed in order.