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By S. Mahandru, Head of Maths at Exam.tips
A resultant force is the single equivalent force which has the same effect as all the individual forces acting on an object.
If all the forces acting on the object are balanced, the resultant force is zero, and the object remains at rest or moves at a uniform speed.
If there are unbalanced forces acting, the object will accelerate in the direction of the resultant force acting through the object.
To determine the resultant:
- In a single dimension, add to or subtract from the forces by the directions in which they act (ie +ve if it is to the right and the –ve if it is to the left).
- In two dimensions, make a vector diagram or apply Pythagoras and trigonometry.
Example
Two forces, one of 3 N to the east and one of 4 N to the north, have a resultant force of 5 N, at an angle of 53° to the east.
If you understand the resultant, you know how and why objects move, and this is the essential link between the force exerted on an object and the motion resulting from it.
Classroom insight: When using Pythagoras to find the resultant, it is important to check the direction. Understanding the magnitude and the angle helps to see the connection with vectors.
