4.2.3—A vector triangle to represent coplanar forces in equilibrium

For three coplanar forces in equilibrium, placing their vectors head-to-tail forms a closed triangle because their vector sum is zero.

Keep each vector’s direction and scale, then use the triangle or sine rule to relate unknown magnitudes. A closed shape is a force-balance test.

For a symmetric load supported by two equal strings, the two tension vectors and the weight close to a triangle.

A force triangle represents vector addition, not the physical shape of the object or the path of motion.