Unbalanced Forces
Elementary School
Definition
Forces acting on an object that do not cancel out, producing a net force. Unbalanced forces cause an object to change its motion—starting, stopping, speeding up, slowing down, or changing direction.
Worked examples
A book rests on a table: \(F_{\)gravity\(} = 10\,\)N down\(\), \(F_{\)normal\(} = 10\,\)N up\(\). Net force = \(0\,\)N\(\) (balanced). Push with \(5\,\)N\(\) right: net force = \(5\,\)N\(\) right (unbalanced) — the book accelerates.
Balanced forces keep the book at rest; adding a push creates an unbalanced force that changes its motion.
A soccer ball rolling on grass experiences \(3\,\)N\(\) friction backward, no forward force. Net force = \(3\,\)N\(\) backward (unbalanced) — the ball slows down and stops.
The unbalanced friction force causes the ball to decelerate until it comes to rest.
Common mistakes
- An object moving at constant speed has unbalanced forces. → Constant speed (no acceleration) means forces are balanced; net force is zero. Unbalanced forces cause acceleration (change in speed or direction), not constant motion.
- If multiple forces act on an object, they are always unbalanced. → Forces are unbalanced only if they don't cancel out to a net force of zero. Equal and opposite forces are balanced even when multiple forces are present.
- Unbalanced forces only make things speed up. → Unbalanced forces cause any change in motion: speeding up, slowing down, or changing direction. Slowing down and turning are also acceleration, caused by unbalanced forces.
Where you'll use it next
You'll apply unbalanced forces in Newton's second law to calculate acceleration, analyze motion in kinematics, study circular motion and gravity, and solve engineering and real-world dynamics problems in physics.
See also
Reviewed by Pat Cheng, M.Ed. — StudyPug Curriculum Lead · Last updated June 6, 2026