The solution of the FirstOrder DifferentialEquation,
dK/dt = K*x
->
x(t) = x(0)*e^(K*t)
Represents a lot of phenomena. Inductors, Capacitors and Resistors have this mathematical form, which is why AnalogComputers can model the RealWorld using ElectricalCircuits. HigherOrder DifferentialEquations can be simplified to FirstOrder.
SeeAlso: ControllabilityAndObservability