System of Forces

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 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.