Definition
An object that has no internal structure, and no physical size.
Discussion
True point particles do not deform or rotate. In reality, it is basically impossible to find a true classical point particle. Luckily, real (macroscopic) objects often behave in a manner similar to a point particle. If an object is rigid and not rotating (or threatening to rotate), you may choose an arbitrary location on that object and follow its movement as if it were a point particle. For instance, if you are analyzing a truck moving down the road, you could choose the location of the front axle to specify the truck's position. If you have a non-rigid object or an object that is going to rotate, you still have the freedom to treat the object as a point particle in the 3-D Motion and Momentum and Force models (and their sub-models) provided you choose to specify the location of the object by the location of its center of mass.