**Kitchen Sink.** Three shelves held up by screws and coat hangers. The
small screw connections at the wall are well-modeled as pin joints. Viewed from
the side, this 2D truss has 6 bars (3 shelve & 3 coat hangers) and 7 joints
(one at the front and back of each shelf, and one at the top), and 8 reaction
forces (2 at the wall end of each shelf and 2 at the top of the top hanger).
Thus, the "rule of thumb, number of equations equal number of unkowns"
formula works: 8 + 6 = 2*7. But this truss is not rigid if not connected to
the wall. The rule of thumb for "rigid when unconnected" does not
work: 3 + 6 < 2*7. Truss assembled at 227 Bryant Ave, Ithaca, NY
on 9/15/02.