 # What are the two main conditions for equilibrium? Verified
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Hint: In physics, equilibrium is the state of a system where neither its state of motion nor its internal energy state changes over time. When a body is either in uniform motion (both translational and rotational) or at rest, it is said to be in equilibrium. We say a body is in static equilibrium in an inertial frame of reference when it neither rotates nor moves in translational motion in that frame of reference.

The following are the two main conditions for equilibrium:
I condition:
The first requirement is that the object's net force be zero. If the net force is zero, there is no net force in any direction.
Let's say $n$ forces are acting on a body:
$F1,{\text{ }}F2,{\text{ }}F3,{\text{ }}......,{\text{ }}Fn$.
${F_1}\; + {F_2} + {F_3} + \ldots \ldots + {F_n}\; = 0$ or $\sum F{\text{ }} = 0$ …… $\left( 1 \right)$
The symbol $\sum$ is a Greek letter called sigma used for summation. The equation $\left( 1 \right)$ is called the first condition of equilibrium.
The first requirement for equilibrium can be expressed as follows in terms of the X and Y components of the forces operating on the body:
${F_{1x}}\; + {F_{2x}} + {F_{3x}} + \ldots \ldots + {F_{nx}}\; = 0$
And,
$F1y + F2y + F3y + \ldots \ldots + {F_{ny}} = 0$
(or)
$\sum Fx = 0$
$\sum Fy = 0$
II condition:
The second criteria are that a rotating item is in equilibrium if its rate of rotation is constant and unaffected by external influences. $\sum \;\tau = 0$

Note:
Examples for the first condition of equilibrium:
On a table, there is a book.
The first criterion for equilibrium is satisfied by a picture hanging on a wall, which is at rest.
A paratrooper falling at terminal velocity also meets the first criteria for equilibrium, indicating that he/she is in equilibrium.
Examples of second condition equilibrium:
The force exerted on the car's steering,
Couple,
The children who were playing in the sea saw.