Final answer:
Net force causes change in motion, as per Newton's second law of motion, resulting in the object's acceleration and therefore a change in velocity. When a net force, such as a kick to a soccer ball, occurs, the object will move or change its state of motion.
Step-by-step explanation:
The correct answer is (b) net force causes change in motion. Net force is the vector sum of all the forces acting on an object. If there's a net force, then the object will experience an acceleration, which means there will be a change in the object's velocity. According to Newton's second law of motion, the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass (Fnet = m * a). Therefore, if a net force acts on a body, it will accelerate in the direction of that net force, which constitutes a change in motion. An example of this is when a soccer ball, which is stationary, is kicked - the force of the kick results in the ball accelerating and moving in a specific direction.
Friction is an example of an external force that often acts as a net force causing a change in motion by slowing moving objects down. We can neglect internal forces such as those holding a body together when we apply Newton's second law because they do not affect the center of mass motion of the system.