Have you ever wondered why jumping up inside a moving train at a constant speed results in landing back in the same spot? This is due to Newton's First Law of Motion—the law of inertia, a cornerstone of physics. This law states that every object persists in its state of rest or uniform motion in a straight line unless compelled to change that state by forces acting upon it. This means that objects possess a "lazy" property, or inertia, which makes them strive to maintain their existing state of motion (including rest). In the model of a train crossing an arched bridge, when a ball is launched vertically, it gains upward velocity in the vertical direction. However, in the horizontal direction, because it has the same horizontal velocity as the train at the moment of launch, and ignoring air resistance, there is no external force acting in the horizontal direction, it will strictly maintain this same horizontal velocity as the train, moving forward at a constant speed. It is this "mainta
