Impact factor — where it appears
Named by 3 essays across one field — each of them below, with the objects they name alongside it.
Twice the deflection, for the same load
A weight placed gently on a beam deflects it by one amount. The same weight let go from rest, a millimetre above the same beam, deflects it by twice as much — and the factor of two is exact, for every structure ever built.
The weight that was dropped
A half-tonne load lowered onto a beam produces 5 kN. The same load dropped one metre onto the same beam produces 160 kN — and onto a beam ten times softer, 54 kN. The stiff structure is the one that suffers, which is the opposite of every other rule on this site.
The train that arrives in time with itself
A single load crossing a span is a mild problem. A train is not one load — its axles are regularly spaced, so the forcing has a frequency of its own, and where a multiple of it lands on the bridge's frequency each coach arrives exactly in step with the motion the last one left behind.
Named alongside it
The objects these essays reach for when they reach for this one.
Dynamic amplificationConservation of energyFree bodyImpulseNatural periodStrain energyAcceleration limitBallastCrane loadingDampingEquilibriumFall arrest