<P> As well as being added, forces can also be resolved into independent components at right angles to each other . A horizontal force pointing northeast can therefore be split into two forces, one pointing north, and one pointing east . Summing these component forces using vector addition yields the original force . Resolving force vectors into components of a set of basis vectors is often a more mathematically clean way to describe forces than using magnitudes and directions . This is because, for orthogonal components, the components of the vector sum are uniquely determined by the scalar addition of the components of the individual vectors . Orthogonal components are independent of each other because forces acting at ninety degrees to each other have no effect on the magnitude or direction of the other . Choosing a set of orthogonal basis vectors is often done by considering what set of basis vectors will make the mathematics most convenient . Choosing a basis vector that is in the same direction as one of the forces is desirable, since that force would then have only one non-zero component . Orthogonal force vectors can be three - dimensional with the third component being at right - angles to the other two . </P> <P> Equilibrium occurs when the resultant force acting on a point particle is zero (that is, the vector sum of all forces is zero). When dealing with an extended body, it is also necessary that the net torque be zero . </P> <P> There are two kinds of equilibrium: static equilibrium and dynamic equilibrium . </P> <P> Static equilibrium was understood well before the invention of classical mechanics . Objects that are at rest have zero net force acting on them . </P>

When does a component of a force do work on an object