In a sound resonating pipe, the closed end must have a node because this is where air particles do not oscillate, allowing for the proper formation of standing waves. An antinode at the closed end would disrupt this formation, as it requires oscillation that cannot occur in a closed environment. The discussion clarifies that while air can move freely from the open end, it cannot oscillate effectively at the closed end. Understanding this distinction is crucial for grasping how sound waves resonate within pipes. The mechanics of longitudinal waves in this context emphasize the importance of nodes at closed ends for efficient sound resonance.