Benchmark

A park bench that only sits level when the people on it balance each other.

Rolled and welded steel, wood two-by-fours, 2010
7′ × 2.5′ × 4′
Professor: Jeffrey Schiff

An empty bench of pale wood slats on black steel legs, on grass against a stone wall; a curved steel rocker is visible under the seat

It looks like an ordinary park bench: wood slats, a black steel frame, arms at each end. But the seat isn't fixed to the legs. It rests on a rolled steel arc underneath, so it rocks from side to side like a seesaw.

In use

Two people sitting at opposite ends of the bench, holding it level

Two people sitting at opposite ends hold it level.

The bench tipped steeply to one side, one sitter sliding down toward the grass while the other rises

When one shifts, the other goes up, and sitting down together becomes something you have to work out with a stranger.

Low view from the end of the bench, two people sitting along it

Two people laughing as the bench tips under them, legs thrown out for balance

Two people talking on the bench, one leaning on the arm, the seat slightly tilted

Drawings

Pencil sketch on graph paper: the bench in elevation with the rocker curve under the seat, the seat frame in plan, and bolt and bracket details

The working sketch: the steel frame in elevation, with the arc under the seat meeting a single pivot, the seat frame in plan, and the brackets and bolts that hold the slats.