1.5 (c) Conditions for equilibrium

Equilibrium of Bodies

When a number of forces acting on a body produce no change in its state of rest or of motion, the body is said to be in equilibrium.

Conditions for equilibrium

The following are two conditions for the body to be in equilibrium

  1. The resultant of all the forces acting on the body should be equal to zero
  2. The resultant moment of all the forces acting on the body about a point should be zero

i.e., the sum of the anticlockwise moments about any point must be equal to the sum of the clockwise moments about the same point.

 Principle of moments

In equilibrium, the sum of the anticlockwise moments about any point must be equal to the sum of the clockwise moments about the same point. This is called the principle of moments

 Couple

Two equal and opposite, parallel forces not acting along the same line form a couple.

The moment of couple is equal to the product of either force and the perpendicular distance between the line of action of both the forces.