If an object's velocity changes, the forces acting on it are what?

• A. Unbalanced forces
• B. Balanced forces
• C. Velocity
• D. Air Resistance

Answer: (A)

When velocity changes, there is a net nonzero force acting on the object. That means the forces are unbalanced—one or more forces are stronger than the others, producing acceleration. According to Newton’s second law, acceleration comes from the total (net) force acting on an object, so a change in velocity signals an unbalanced net force. If all forces balanced each other, the velocity would stay the same, because there would be no acceleration. Air resistance is just one possible force that could be part of that unbalanced set, depending on the situation. The key idea is that a change in velocity shows there’s a net force acting.