Resultant Force

The resultant force is the vector sum of all forces acting on an object.

If forces act along the same line, add those in the same direction and subtract those in the opposite direction.

For forces at right angles, use Pythagoras’ theorem to find the magnitude and trigonometry to find the direction.

If the resultant force is zero, the object is in equilibrium (stationary or moving at constant velocity). If the resultant force is non-zero, the object accelerates in the direction of the resultant force ($F = ma$).