Coplanar Forces:

Forces working in the same plane are called as coplanar forces. In figure forces a and b¯ are working in vertical plane ABCD. They are called as coplanar forces. Forces C¯ and d¯ are also called as coplanar forces as they are working in one plane, say, BCGF. But forces a and c are not coplanar forces as they are working in two different planes. If all of the forces working on a body meet at a point, they are called as concurrent forces. Forces a, b¯ and C¯ illustrated in figure are concurrent forces as they are meeting at a particular point O, whereas forces d¯ , e¯ and  f¯ are called as non-concurrent forces because all three forces are not meeting at a point.

Coplanar forces may also be classified as parallel forces and non-parallel forces. If the lines of action of forces are parallel, after that the forces are called as parallel forces. If the forces point the similar direction, they are called as parallel forces and if they point in opposite directions, they are called as unlike parallel forces. Forces p¯ and q¯ are like parallel forces, whereas q¯ and r¯ or p¯ and r¯ are unlike parallel forces as illustrated in Figure. Forces s¯ , t ¯and u¯ are non-parallel forces. Concurrent forces are non-parallel forces. However, non-parallel forces can be concurrent or non-concurrent.