Here is a puzzler I once posed for a fellow physics student. I have the correct answer... but can you figure it out? Picture a box shaped car with open side windows on a circular track. Suppose it is raining but there is no wind so the rain falls straight down. When the car is stationary the rain will just miss the bottom edge of the side windows so that no rain gets inside...but just barely. Now for the question. When the car begins moving around the circular track will rain get into the car? It would seem from a stationary observer's frame that since the rain is vertical and the windows are vertical no rain should ever get into the car. It would seem from the perspective of someone inside the car that there is a centrifugal acceleration pulling all objects away from the center of the track and by Einstein's equivalence principle this is no different from a gravitational force doing the same thing. So a few of the rain drops should "curve" in through the window. Or should they? So which is it?