Static force analysis. If components of a machine accelerate, inertia is produced due to their masses. However, the magnitudes of these forces are small compares to the externally applied loads. Hence inertia effect due to masses are neglected. Such an analysis is known as static force analysis. • What is inertia? • The property of matter offering resistance to any change of its state of rest or of uniform motion in a straight line is known as inertia.
• Necessary and sufficient conditions for static and dynamic equilibrium are • Vector sum of all forces acting on a body is zero • The vector sum of the moments of all forces acting about any arbitrary point or axis is zero.
STATIC FORCE ANALYSIS AND DYNAMIC FORCE ANALYSIS • If components of a machine accelerate, inertia forces are produced due to their masses. If the magnitude of these forces are small compared to the externally applied loads, they can be neglected while analysing the mechanism. Such an analysis is known as static force analysis. • If the inertia effect due to the mass of the component is also considered, it is called dynamic force analysis.
D’Alembert’s principle • D’Alembert’s principle states that the inertia forces and torques, and the external forces and torques acting on a body together result in statical equilibrium. • In other words, the vector sum of all external forces and inertia forces acting upon a system of rigid bodies is zero. The vector sum of all external moments and inertia torques acting upon a system of rigid bodies is also separately zero.