A footballer kicks a stationary ball. The ball accelerates across a grass pitch and then gradually slows down before stopping. Explain why the ball accelerates when kicked and why it eventually stops, using Newton's laws of motion.

When the foot strikes the ball there is a force from the foot that is not balanced by any other force, so a resultant force acts on the ball. By Newton’s Second Law this unbalanced force produces an acceleration of the ball in the direction of the force.

After the ball leaves the foot it is no longer acted on by the foot, but it is still subject to forces from the grass. The grass exerts a frictional force on the ball that is opposite to the direction of motion. This frictional force is a resultant force that causes the ball to decelerate. When the ball finally comes to rest the forces on it are balanced, so by Newton’s First Law it remains at rest.