Force Systems

• A moment is equivalent to a couple. A curved arrow is used to indicate the resultant of a couple.

• Resultant of parallel forces. For a system of parallel forces, the resultant is a single force whose magnitude is equal to the sum of the forces, whose direction is parallel to those forces, and whose location is such that moment of the resultant about a point is equal to the sum of the moments of the forces.

• Center of Gravity. Center of gravity is point where the resultant of the force of gravity acts on an object. The position of the center of gravity can be calculated as the resultant of parallel forces.

• Equilibrium of a rigid body. For a body in two dimensions, equilibrium means that the sum of the X components is zero, the sum of the Y components is zero, and the sum of the moments is zero about any point.