The basic knowledge of various kinds of forces and motion is highly desirable for engineering and practical applications. The Newton’s laws of motion defines and gives the expression for the force. Force is a vector quantity and can be combined according to the rules of vector algebra. A force can be graphically represented by a straight line with an arrow, in which the length of the line is proportional to the magnitude of the force and the arrowhead indicates its direction.

Fig: Concurrent forces

**Concurrent Forces:** A force system is said to be concurrent, if the lines of all forces intersect at a common point.

**Coplanar Forces**: A force system is said to be coplanar, if the lines of the action of all forces lie in one plane.

Fig: Coplanar forces