1. A computerized method comprising: providing, by a computer system, a user interface for creating a game, the user interface facilitating user selection of parts for the game; placing, by the computer system, a set of parts selected by a user in a three-dimensional (3D) world; automatically detecting, without user interaction, by the computer system, adjacent parts within the set based on proximity of surfaces of the parts in the 3D world while parts are being moved during editing operations of the user; upon detecting the adjacent parts, automatically determining, without user interaction, joint types for the adjacent parts based on surface types of the adjacent parts; automatically creating, without user interaction, by the computer system, one or more rigid joints of the determined joint types between the adjacent parts, wherein at least some of the adjacent parts are primitive geometric shapes selected by the user for joining with other parts in the set, the primitive geometric shapes including at least one of a block, a wedge, a cylinder and a sphere; forming one or more models for the game from the set of parts that comprises parts automatically joined, without user interaction, using the one or more rigid joints; physically simulating, by a rigid body physics engine, motion of joined parts having one or more rigid joints in the game and motion of the one or more models in the game using one or more properties, wherein the one or more properties specify one or more of an event to occur when joined parts having one or more rigid joints collide during simulation and whether joined parts having one or more rigid joints are intended to collide during simulation; detecting, by the physics engine, a first collision between the joined parts having one or more rigid joints in the 3D world during physical simulation of the motion of the joined parts having one or more rigid joints and the one or more models; simulating, based on the one or more properties, a behavior of the joined parts having one or more rigid joints that results from the first collision; allowing a user to modify one or more properties of joined parts having one or more rigid joints, the joined parts selected by the user in the 3D world; and simulating, based on the modified properties, a modified behavior of the joined parts having one or more rigid joints that results from a second collision.