I hope this is the right place for this kind of question - please forgive me if it isn't. I am wondering about the expected effect of acceleration and/or motion on a pendulum clock. It pertains somewhat to relativity theory, but [to my understanding] it is equally a mechanical engineering question. If a pendulum clock is put on a train and the train accelerates to an inertial speed, will that clock tick at the same rate as a similar clock left behind in the train station (at rest on earth)? If not, does anyone know by how much it would change? Also, if a pendulum clock was built on a train traveling at an inertial speed, such that it didn't undergo acceleration, would it be expected to tick at the same rate as a clock in the train station? Am I right in presuming that a pendulum clock would not work in deep space? Also, if acceleration is the same as gravity, or at least has the same effect, would a pendulum clock accelerating in deep space start to tick, given the correct orientation? Apologies for the glut of questions, it's just something I've been wondering about.