Peculiarities of Body Balance on Hinged Supports and Sliding Closure

 The equilibrium of a body supported by rigid and telescopic supports on fixed hinges is considered. It is shown that the addition of a potentially sliding joint may not provide mobility to the design, as well as the addition of a rotary joint. A paradox was discovered for a sliding support: the equations of seemingly obvious equilibrium are not fulfilled. Deviations are introduced to regularize the problem. Internal reactions remain statically indeterminate, while the magnitude of these reactions may be significant. It is shown that external reactions tend to infinity as the introduced deviations decrease. This explains the inconsistency of the equilibrium equations: a pair of infinite forces with zero leverage, generally speaking, is not equivalent to zero force, but can create any moment, including the balancing moment of gravity. It can be assumed that some of the major accidents involving building structures are associated with these features.