Final answer:
A force whose lines of action all lie within the same plane is referred to as a coplanar force in physics. These forces are essential for analyzing the behavior of objects when applying Newton's laws of motion in two dimensions.
Step-by-step explanation:
The force being described, where the lines of action all lie within the same plane, is typically referred to in physics as a coplanar force. Coplanar forces exist in a two-dimensional plane and are important when analyzing the forces acting on a body in that plane. For example, all the forces acting on an object sliding down an incline are coplanar.
When studying forces and free-body diagrams, such as in the analysis of objects on an inclined plane, one must consider the components of weight, which can be broken down into parallel and perpendicular components relative to the incline. These components are coplanar with the incline's surface. Likewise, friction, normal force, and any applied forces in the same plane are also considered coplanar.
Understanding the concept of coplanar forces is crucial in physics, particularly when applying Newton's laws of motion, where the simplification to two dimensions greatly aids in problem-solving and understanding the physical behavior of systems.