Final answer:
The location where all the lines of force in a body converge and assumed to be concentrated is the center of gravity, which is essentially the same as the center of mass in a uniform gravitational field.
Step-by-step explanation:
The location where all the lines of force in a body come together is known as the center of gravity. The center of gravity is the point where the total weight of the body is assumed to be concentrated. For objects in a uniform gravitational field, such as those on Earth's surface, the center of gravity is effectively the same as the center of mass. This is because the acceleration due to gravity is constant over the object. Only when the gravitational field is nonuniform across an object, such as for very large objects in space, do the center of gravity and the center of mass differ.
The concept of the center of mass is important in understanding the motion of an object. It is the weighted average position of all the mass in a system and can be used to predict the movement of a system's mass in space. The center of mass follows the trajectory according to Newton's second law when acted upon by an external force. Even large bodies, like cruise ships, operate under the assumption that their entire mass is concentrated at their center of mass.