Those who come to Cambridge soon learn that the fastest route between Harvard and MIT is by the subway. For many students, this short ride is a quick and easy way to link physics and calculus. A simple, homemade accelerometer provides all the instrumentation necessary to produce accurate graphs of acceleration, velocity, and displacement position on this subterranean route. Each graph, in turn, reveals a story of the train's trip: speeding up and braking, varying track conditions, top speed, and the distance between subway stops deep beneath Massachusetts Avenue. (Contains 4 figures.)