We present a framework to design force fields that drive particles to follow a path under the physics-based animation system. In this framework, a user interactively specifies the desired path, represented by a Bezier curve using a GUI and the attraction force that drives a particle toward the target location. Then, the framework automatically defines the steering force to make a particle follow the desired path. To this end, we use B-splines to define the steering force that best approximates the user-specified path. We demonstrate the effectiveness of our method by showing a large number of particles following the desired path and forming an animated human figure. Our method creates a stable behavior of particles and is fast enough to run in real time