Duration of Impact of Bars.

Abstract

Duration of Impact of Two Spheres.---The Hertz theory was verified by experiments with brass and cast-iron spheres of 3.8 and 7.6 cm. diameter respectively, using a condenser discharge method of measuring short time intervals which gave accurate results for intervals of the order of ${10}^{\ensuremath{-}4}$ second.Duration of Impact of Bars.---Experiments with hot-rolled steel bars, 2.86 cm. in diameter and 16 to 62 cm. long, prove that the compressional wave theory is inadequate since the duration of impact was found to be a function of the initial velocity and to be proportional not to the first power of the length of the shorter bar but more nearly to the two-fifths power. Moreover, the fundamental assumption of the compressional wave theory was shown to be wrong by means of a model in which the wave velocity was slow enough to be observed. A theoretical expression was then derived on the basis of certain assumptions as to the distribution of pressure and its variation with the displacement of the center of mass of the colliding body, which agrees in general with the experimental results.