Final answer:
According to Newton's 1st Law of Motion, the ball will continue to move forward until it hits a wall, where the external force causes it to stop and fall down.
Step-by-step explanation:
According to Newton's 1st Law of Motion, an object will continue to move in a straight line with constant speed unless acted upon by an external force. When you throw a ball, it has an initial velocity that keeps it moving forward. However, when the ball hits a wall, the force exerted by the wall acts as an external force and causes the ball to stop and fall down.
Learn more about Newton's 1st Law of Motion