A swinging bob toy having an outer bob and middle bob on a string, with the middle
bob having a bore through which the string passes to allow the middle bob to slide
along the string. The middle bob has a substantially toroidal, liquid-containing
bladder. The mass of the liquid contributes substantially to the overall mass of
the middle bob, but the viscosity of the liquid and the dimensions of the bore
of the toroid are such that the dynamic moment of inertia (i.e., a moment of inertia
dependent on linear and/or rotational velocity and/or acceleration, of a history
thereof) is small as the middle bob begins its rotation as the outer bob passes
the top of its orbit. The viscosity of the liquid is small enough that as the outer
bob traverses the top of its orbit the dynamic moment of inertia is small and the
string does not tangle about the middle bob, yet large enough that as the outer
bob traverses the bottom of its orbit the rotation of the middle bob is slowed
and the string tension does not exhibit a rapid peak.
