SR section 1.7. Einstein states if a train and light beam are moving in the same direction, the speed of the light as seen from the train is c-v. ( c being the speed of light and v the speed of the train ). c-v being smaller than c is resolved by time dilation or length contraction. My question is, in c-v, what is the train's speed relative to? Given light's speed is being measured relative to the train, shouldn't the train's speed also be measured relative to the train? As the train's speed relative to itself is zero, this means c-v , no matter what v's speed is, always gives c. Separate question. Do objects aligned sideways, or vertically along their direction of travel contract, as objects aligned lengthways do? If so shouldn't the terminology change? e.g direction of motion contraction?