Table 1. Linear response in mechanical and chemical systems.

Physical quantity	Mass-spring system	Chemical system
Coordinate	Displacement	Receptor occupancy, δn = n - n̄
Conjugate force	f	Free energy change δF = kBT (δk+/k+ - δk−/k−)
Spring constant	κ	kBT/[n̄ (1 - n̄)]
Damping constant	γ	kBT/(k−n̄)

The response of a chemical system near equilibrium is directly analogous to that of the familiar mass-spring system in a viscous fluid, in the limit that the inertial term, MẊ, can be neglected (valid for κ/M ≪ γ²/4).