Principle of Moments

The principle of moments, or Varignon's theorem, describes the equilibrium of a rigid body under the action of forces.

It states that the moment of a force about a point is equal to the sum of the moments of the components of the force about the point.

The moment of a force at a point is the product of the perpendicular distance from the point of application and the applied force.

It can also be determined by resolving the force into its components and multiplying individual components with the corresponding moment arm.

Consider a valve where a hand wheel is mounted on a pipeline. When a force is applied to rotate the wheel, the moment of the force about the center can be determined by multiplying the magnitude of force by the perpendicular distance from the center to the point of application.

The applied force can also be resolved into its components, and the moment can be determined by adding the products of each force component with its corresponding distance.