Video narration
Why should a soccer ball stop moving by itself after you kick it? Before the kick, it stays still until your foot changes its motion. Afterward, you stop pushing; it rolls on. If no unbalanced force acted on it, the ball would continue in a straight line at constant speed. That resistance to change is called inertia. So why does the real ball stop? Here's the flip: motion does not simply run out. Friction under the ball acts as an unbalanced force, opposing its motion. Air resistance helps too, slowing the ball until it rests. Newton's first law says rest stays rest, and straight, constant-speed motion continues unless an unbalanced force changes it. So the kick starts motion, but a continuing push is not needed to maintain it. Because friction is the unbalanced force: without it, the ball keeps moving; friction changes its motion and stops it.