5.7 : Equations of Equilibrium in Three Dimensions

When analyzing structures or systems at rest, it is necessary to ensure they are in equilibrium. This is where the vector and scalar equations of equilibrium come into play. These equations are crucial in ensuring a structure is stable and will not collapse or fall apart. The vector and scalar equations of equilibrium provide a framework for analyzing the forces acting on a body.

According to the vector equations of equilibrium, the vector sum of all the external forces acting on a body must equal zero. Furthermore, the vector sum of the couple moments and the moments of all the forces about a point must also be equal to zero.

The scalar equations of equilibrium state that if the external forces are expressed in the Cartesian form, then summation of the components of the forces along the respective directions must be zero.

Similarly, the scalar summation of the components of a moment in the x, y, and z axes must also be zero.

These equations are fundamental in mechanical engineering, ensuring that structures are safe and stable.