Abstract. In the rod and hole paradox as described by Rindler (1961 Am. J. Phys. 29 365–6), a rigid rod moves at high speed over a table towards a hole of the same size. Observations from the inertial frames of the rod and slot are widely different. Rindler explains these differences by the concept of differing perceptions in rigidity. Grøn and Johannesen (1993 Eur. J. Phys. 14 97–100) confirmed this aspect by computer simulation where the shapes of the rod are different as observed from the co-moving frames of the rod and slot. Lintel and Gruber (2005 Eur. J. Phys. 26 19–23) presented an approach based on retardation due to speed of stress propagation. In this paper, we consider the situation when two parallel rods collide while approaching each other along a line at an inclination with their axis. The collisions of the top and bottom ends are shown to be reversed in time order as seen from the two co-moving frames. This result is explained by the concept of 'extended present' derived from the principle of relativity of simultaneity.

Print publication: Issue 4 (July 2006)
Received 24 March 2006, in final form 5 April 2006
Published 8 May 2006