Which forces cause a change in the motion of an object?

• A. Balanced forces
• B. Unbalanced forces
• C. Net force
• D. Newton

Answer: (B)

Motion changes when the forces acting on an object don’t cancel each other out. The overall push or pull on the object, called the net force, determines whether it speeds up, slows down, or changes direction. If all forces balance, the net force is zero and motion doesn’t change. If the forces are unbalanced, the net force is nonzero and causes acceleration in the direction of that net force.

So the key idea is unbalanced forces lead to a change in motion because they produce a nonzero net force. For contrast, balanced forces produce no change in motion, and a term like Newton isn’t a force itself (it’s the name of the scientist and the unit of force), so it doesn’t cause motion.