4.1.2—The vector nature of force

Forces combine by vector addition, so their lines of action and directions matter. A force can be resolved into components along convenient axes without changing its physical effect.

Use a consistent axis system, resolve oblique forces with sine/cosine, and interpret a negative component as opposite to the chosen positive direction.

Two 10 N forces at right angles have resultant 10√2 N, not 20 N; two opposite 10 N forces have resultant zero.

Adding magnitudes ignores angle and can overestimate the resultant.