# Basic Principles of Statics-Static Equilibrium, Static Determinacy, forces,Resolution of Forces

The statics is the branch of engineering mechanics that deals with the equilibrium of body at the state of rest under the action of forces.

### What is Static Equilibrium in Engineering Mechanics?

A planar structural system is said to be in the state of static equilibrium when the resultant of all the forces and moments is equal to zero. If we consider a two-dimensional system (X-Y), then the sum of the forces and moments in each direction can be given by:
1. Î£Fx = 0
2. Î£Fy = 0
3. Î£Mx = 0
4. Î£My = 0

### What is Static determinacy?

A body under the action of coplanar forces must follow the static equilibrium conditions

### What is a Force?

A force is defined as a cause that tends to alter the state of rest of the body or state of uniform motion in a straight line. It is also defined as the product of the mass of the body on which the force is acting and the acceleration of the force. This is given by the relation:
P = ma
Here, m= mass of the body in kg; a = acceleration caused by the force in m/s2

Note: The SI Unit ( System International Unit) for force is kg m/s2 or Newton(N);Â
Â  Â  Â  Â  Â  Â 1 kN = 1 000 N, 1 MN = 1 000 000 N

### Resolution of Forces

The total effect of a set of forces acting on a body can be conveniently calculated by determining the resultant of all the forces acting on the body. The vector components of each force are determined along x and y direction at first. After which the resultant is determined.
As shown in the figure above, the vector components of the force F is Fy and Fx. If F is making a angle Î¸ with the X-axis, then the vector components:

1. Fx = FsinÎ¸
2. Fy = FcosÎ¸