Concept
Tuned mass damper — where it appears
2 essays name this object, across one field. What follows is each of them, and the objects they name alongside it.
The bridge that was pushed by its own sway
A crowd walking on a bridge that moves sideways adjusts its footing to stay balanced, and the adjustment pushes the bridge the way it is already going. The crowd is a damper with the sign reversed, and past a certain number of people the total damping is negative.
The mass that helps by being late
Hang three per cent of a building's mass from a spring in its roof, tune the spring so the mass arrives a quarter-cycle behind the motion, and the peak response falls by a factor of seven. Nothing was strengthened and nothing was stiffened.
Named alongside it
The objects these essays reach for when they reach for this one.
DampingCrowd loadingDetuningFixed pointsFootbridgeLateral vibrationMass ratioMode shapeNegative dampingResonanceSelf excitationStability threshold