The control of underactuated robot manipulators provides a significant challenge to the robotics engineer. The Acrobot is a simple underactuated system consisting of a double pendulum with an actuator at only the second joint. Previous work has shown how linearization methods can achieve the tracking of slow inverted trajectories. In this paper we derive a surprising set of exact trajectories of the nonlinear equations of motion, which involve inverted periodic motions. The trajectories can be made arbitrarily fast by appropriate choice of the Acrobot mass and length parameters. Next, we present a nonlinear control law (which has appeared elsewhere) and show how it can be applied to the Acrobot to track these trajectories. In simulations we compare tracking results for our controller and one based on pseudolinearization. The pseudolinearizing controller produces significant error for a 1 Hz trajectory, while ours produces none. Finally, we present experimental results which demonstrate that the assumptions of the theory were not overly restrictive. In particular, peak-to-peak oscillations of joint 2 as large as 85 were obtained, despite real-world effects, such as joint friction, inexact parameter values, and noisy and delayed joint velocity data.