Point Particle Model

In many physics problems, we can simplify extended objects by treating them as point particles. Instead of tracking every part of an object, we replace it with a single point located at its center of mass (COM).

When an object moves from one place to another without rotating, we can model its entire mass $M$ as concentrated at the center of mass. This lets us describe the motion of a car, a book, or a planet using just one set of coordinates.

When does this work? The point particle model is excellent for analyzing translational motion—the overall motion of an object from place to place. It simplifies our analysis dramatically.

When does this fail? The approximation breaks down when rotation matters. If an object is spinning or tumbling, we cannot ignore its size and shape. Similarly, if different parts of the object experience very different forces, the point particle model may not capture the full physics.

For now, we focus on situations where the object's motion can be described by tracking its center of mass.