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
|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 Non-concurrent 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||Non-coplanar parallel forces||All the forces are parallel to each other, but not in the same plane.||The weight of benches in a classroom.|
|7||Non-coplanar 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||Non-coplanar non-concurrent 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.|