This paper considers the problem of designing and implementing a stabilizing controller for an electromechanical system, called the ball and arc system. This system is nonlinear and underactuated. Moreover, the equilibrium of this system is open-loop unstable. Stabilization of this system is a challenging task and it is suitable for serving as a testbed for research and education in nonlinear control systems. In this paper, the mathematical model of the system is derived to facilitate the controller design. Based on sliding mode control, a stabilizing controller is designed to achieve locally asymptotic stability of the system. The experimental apparatus is constructed, and the controller is implemented. The simulation and experimental results are given to demonstrate the effectiveness of the control scheme.