This is an intuitive physics study of collision events. In two experiments the participants were presented with a simulated 3D scene showing one sphere moving horizontally towards another stationary sphere. The moving sphere stopped just before colliding with the stationary one. Participants were asked to rate the positions which both spheres would have reached after a fixed time if the collision had really occurred. The simulated masses of both spheres and the velocity of the moving one were manipulated. Specifically, in Experiment 1 different implied masses were defined by varying only the size of the spheres; in Experiment 2, different implied masses were defined by varying both the size and the apparent texture (material) of the spheres. Functional Measurement was used to compare the physical laws of collision events with cognitive integration rules. Cognitive rules proved to be more similar to physical laws in Experiment 2, i.e., when both spheres size and apparent texture were manipulated. Surprisingly, in both experiments only half the participants took into account the possibility that the moving sphere could have bounced back after the collision. These and other results are important for teaching elementary physics. (Contains 5 figures and 5 footnotes.)