Consider some material object, more or less rigid, with two ends, A and B, like A---B It is at rest at a point in time t_0 in my reference frame. Now I kick it a bit, i.e. I apply some force for a limited amount of time at A in the direction of B. After the kick, the whole object has a speed v in the direction A->B. I reckon that the speed of B, v_B, is never larger than that of A, v_A, before, during and after the whole experiment. Now I consider how, during application of the force, the force propagates through the object from A to B. The speed of propagation is limited by the speed of light c. As a consequence it seems that during the force application, there is a small time interval where v_B<v_A. Integration of this delta-speed translates into a reduction of the distance between A and B at the end of the experiment. If I did not make a mistake, the reduction factor is (1-v/c). This is a stronger reduction even than the relativistic length contraction factor. How can I get the object longer again to match the relativistic contraction? To me it feels wrong to argue with material dynamics to fix an effect that directly results from a very basic principle. Ideas? Harald.