Calculations involving forces

The resultant force is a single force that has the same effect as two or more forces acting together. You can easily calculate the resultant force of two forces that act in a straight line.

Two forces in the same direction

Two forces that act in the same direction produce a resultant force that is greater than either individual force. Simply add the magnitudes of the two forces together.

Example

Two forces, 3 newtons (N) and 2 N, act to the right. Calculate the resultant force.

3 N + 2 N = 5 N to the right

Two arrows, one above the other, both pointing to the right, one labelled 2 N and one labelled 3 N. Then an equals sign and then another arrow to the right labelled 5 N.Two forces acting in the same direction

Two forces in opposite directions

Two forces that act in opposite directions produce a resultant force that is smaller than either individual force. It is often easiest to subtract the magnitude of the smaller force from the magnitude of the larger force.

Example

A force of 5 N acts to the right, and a force of 3 N act to the left. Calculate the resultant force.

5 N - 3 N = 2 N to the right

Two arrows, one above the other, one pointing to the left, labelled 2 N, the other pointing to the right labelled 3 N. Then an equals sign, with an arrow to the right labelled 1 N.Two forces acting in opposite directions

Free body diagrams and vector diagrams - Higher

Free body diagrams are used to describe situations where several forces act on an object. Vector diagrams are used to resolve (break down) a single force into two forces acting at right angles to each other.

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