A point mass is a theoretical object in physics that has mass but no physical size or dimensions. It is often used to simplify calculations in systems where the size of the object is not relevant.
The mass of a point mass is calculated by dividing the force acting on it by its acceleration. This formula is known as Newton's Second Law of Motion: F = ma, where F is force, m is mass, and a is acceleration.
An extended object is a physical object that has size and dimensions, unlike a point mass. It can be any object with measurable length, width, and height, such as a book, a car, or a planet.
The mass of an extended object is calculated by adding the masses of all its individual point masses. This is because an extended object can be thought of as a collection of many point masses, each with their own mass and location.
The main difference between point masses and extended objects is that point masses have a single, concentrated mass located at a specific point, while extended objects have their mass distributed throughout their physical dimensions. This means that point masses have a fixed mass, while the mass of an extended object can vary depending on the distribution of its mass.