Dynamic Equilibrium in translation

• If an object is assumed as a particle during rectilinear motion analysis, all the forces that interacts the object is align on the axis that coincides the particle located at the center of gravity.
• In reality, this assumption may not be valid especially for objects that have considerable size.
• The resultant of all external forces produces an acceleration at the center of gravity
• The equilibrant force of the resultant force is known as the REF (Reversed Effective Force). (From D’Alembert’s Principle)
• REF are also called the inertia forces of the particles
• REF and the resultant is equal in magnitude, but opposite in direction acting through the center of gravity. REF is always directed opposite the acceleration