Toy models for the falling chimney

In this paper we review the theory of the "falling chimney," which deals with the breaking in mid-air of tall structures when they fall to the ground. We show that these ruptures can be caused by either shear forces typically developing near the base, or by the bending of the structure which is caused primarily by the internal bending moment. In the latter case the breaking is more likely to occur between one-third and one-half of the height of the chimney. Small scale toy models are used to reproduce the dynamics of the falling chimney. By examining photos taken during the fall of these models we test the adequacy of the theory. This type of experiment, which is easy to perform and conceptually challenging, can become part of a rotational mechanics lab for undergraduate students. (C) 2003 American Association of Physics Teachers.