The mechanical analog of a capacitor is the compliance of a
spring. The voltage across a capacitor corresponds to the
force used to displace a spring. The charge stored in
the capacitor corresponds to the displacement of the spring.
Thus, Eq. (C.2) corresponds to Hooke's law for ideal springs:
where is called the spring constant or spring
stiffness. Note that Hooke's law is usually written as
. The quantity is called the spring compliance.