When resultant force is zero, an object remains at rest or continues at constant velocity. Zero resultant does not require the absence of all forces; individual forces can balance. A change in speed or direction requires a resultant force; inertia is the tendency to resist changes in motion. Example: State motion when a moving object has zero resultant force. Constant velocity. Distinguish the observation from the explanation, and support any judgement with evidence. Give a reason. Use evidence.