Coplanar and Non-Coplanar Forces:

In this unit, you have learnt to identify the different systems of forces. You have also learnt the many techniques of adding the forces to get the resultant of the system of forces, for example. use of law of parallelogram of forces or triangle or polygon law of forces. The significant equations to remember are:

                                                       R = P + Q

tan θ = Q sin α/ (P + Q cos α)

tan β = P sin α / (Q + P cos α)

Here,   R is the resultant of P and Q ,

α = angle between P and Q,

θ = angle between R and P,

β = angle between Q and R.

The resultant of system of forces is the simplest force system that may replace the original forces without changing their external effect on a rigid body. Following table gives the probable resultant force system for the several systems of forces: