When the object is motionless even with two or more forces applied on the object, these forces are in an equilibrium state.

(1) Equilibrium of forces applied on a single point

- For a tug of war, the rope position does not move when this rope is being pulled towards opposite directions at the same strength of forces. This is an equilibrium state of forces (See the below figure).

- When the resultant forces are the same in opposite directions, it will create an equilibrium of forces even though the forces are not applied on the same line.

- When a force is applied from the opposite direction of the resultant force, forming a triangle of forces, these forces are in an equilibrium state. In this case, the polygon of forces is closed in the same direction (see the right image shown below).

(2) Case example of force equilibrium in mechanical equipment

- For high-speed and high-precision motion control of a heavy movable body, the mechanism with equilibrium of forces applied may be incorporated into the design in order to reduce the load burden on the movable body.

- For the vertical drive control mechanism in particular, keep the forces in equilibrium by adding a spring (see the images below), an air cylinder, or a pulley on one side and placing a weight on the other side.

In order to bring out the high-speed drive performance of a linear motor (shaft motor), the spring suspension structure has been adopted for weight reduction of the vertical movable body.