The increased stiffness of rubber for a high-speed compression
can be modeled approximately by the relation
m d2y/dt252ky2g dy/dt, where k is the effective spring
constant and g dy/dt is a velocity-dependent force term related
to the viscosity of the rubber.7,10 Such a model results
in a hysteresis curve of finite area since the model equation
describes damped harmonic motion. The hysteresis curve in
this case commences with y50 and F52gv1 at t50.