Splat asked, to paraphrase, "Won't it violate relativity when you try to throw a ball forward from a train moving 1kps less than light speed, as the ball's inertia will be prohibitive and will not accelerate normally?" And I answer that this commonly accepted "inertia" explanation of why things cannot move at light speed is hooey. The ball itself and the force throwing the ball are both in the same frame of reference and so no mass increase phenomenon will be evident. That mass increase thing is misleading and has been widely misinterpreted and Science is backing straight away from said "notational fiction". The answer is, the ball will accelerate perfectly normally, but as another poster said, by the Addition of Velocities formula (of Relativity), the sum of the velocities will still be less than C. See also http://www.ezrelativity.tk This scenario unfolds at every baseball game, as, according to 'observers' on some distance fast-receding galaxies, Earth is already moving at near light speed.