Final answer:
In physics, boundaries define the system and the point of contact between objects, spaces, and forces, allowing distinction between internal and external forces as per Newton's Laws.
Step-by-step explanation:
In physics, boundaries define the system and the point of contact between objects, spaces, and forces. By understanding the nature of these boundaries, one can determine which forces affect the system, distinguishing between internal and external forces. External forces originate from outside the system and can affect the system’s motion, while internal forces are interactions within the system itself and often cancel each other out in terms of effecting motion. This concept is crucial for the correct application of Newtons's Laws and is extensively applied throughout various areas of physics.