Relativistic elasticity of rigid rods and strings

Abstract: After a brief discussion of relativistic elasticity, we consider rigid one-dimensional elastic bodies (i.e. rods or strings whose speed of sound is equal to the speed of light) in a few simple examples: a rigid rod colliding with an unmovable wall, a rigid rod being pushed by a constant force, a rigid string whose endpoints are simultaneously set in motion (seen as a special case of Bell's spaceships paradox), and a radial rigid string that has partially crossed the event horizon of a Schwarzschild black hole while still being held from the outside.