Balanced and unbalanced forces

The resultant or net force combines forces on one object. Add forces in the same direction; subtract opposing forces. A non-zero resultant points toward the larger total. Equal opposing totals give balanced forces and zero resultant. A stationary object can remain stationary; a moving object can keep constant speed in a straight line.

An unbalanced force changes velocity: speed, direction or both. A force opposite existing motion can slow an object, without instantly stopping it. Turning requires an unbalanced force even at constant speed. Under comparable conditions, a larger resultant changes motion more strongly; greater mass is harder to accelerate with the same resultant. Keep existing motion separate from resultant-force direction.

Watch out: Balanced forces mean no change in velocity. Constant straight-line motion is also possible.