A triangular localized potential energy has forces +F behind and −F ahead of the trap centre. With vc=F/ζ=Lfc, α=2X0/L and β=fT/fc, its circular response is fp/fc=αβ/(β2−1+α) for β>1. A trapped particle has fp/fc=β for 0≤β≤1, interpreting the discontinuous force at the cusp by a sticking or rounded-well limit.
