When several forces of different magnitude and different direction act upon a certain body, they constitute a system of forces.
If all the forces in a system lie in a single plane, it is called a coplanar force system.
If the line of action of all the forces in a system passes through a single point it is called a concurrent force system.
In a system of parallel forces, all the forces are parallel to each other.
If the line of action of all forces lies along a single line, then it is called a collinear force system.
The various system of forces, their characteristics and examples are given in the table below.
Table: System of Various Forces
S.No  Force System 
Characteristic

Examples


1  Collinear forces  Line of action of all the forces acts along the same line.  Forces on a rope in a tug of war. 
2  Coplanar parallel forces  All forces are parallel to each other and lie in a single plane.  The system of forces acting on a beam subjected to vertical loads. 
3  Coplanar like parallel forces  All forces are parallel to each other, lie in a single plane and are acting in the same direction.  The weight of a stationary train on a rail when the track is straight. 
4  Coplanar Concurrent forces  Line of action of all forces pass through a single point and forces lie in the same plane.  Forces on a rod resting against a wall. 
5  Coplanar Nonconcurrent forces  All forces do not meet at a point but lie in a single plane.  Forces on a ladder resting against a wall when a person stands on a rung which is not at its centre of gravity. 
6  Noncoplanar parallel forces  All the forces are parallel to each other, but not in the same plane.  The weight of benches in a classroom. 
7  Noncoplanar concurrent forces  All the forces are parallel to each other, but not in the same plane, but their lines of action pass through a single point.  A tripod is carrying a camera. 
8  Noncoplanar nonconcurrent forces  All forces do not lie in the same plane, but their lines of action pass through a single point.  Forces are acting on a moving bus. 