  The dynamic impedance of a sphere oscillating in an elastic medium is
considered. Oestreicher's formula for the impedance of a sphere bonded to the
surrounding medium can be expressed simply in terms of three lumped impedances
associated with the displaced mass and the longitudinal and transverse waves.
If the surface of the sphere slips while the normal velocity remains
continuous, the impedance formula is modified by adjusting the definition of
the transverse impedance to include the interfacial impedance.
