Statics

Statics, the branch of dynamics which treats of equilibrium. The ordinary Balance (q.v.) is one of the most important of statical instruments. With it we balance the weight of a body of unknown mass against the combined weights of a number of standard masses, and so determine the unknown mass in terms of recognised units. The general principle of statics is that which describes the condition of equilibrium amongst a number of given forces. The condition is that the vector sum of the moments of the forces about any and every point vanishes. It is more usual in text-books to break this statement up into two, which admit of ready application. The first is that the sum of the components of the forces along each of three non-coplanar directions vanishes; and the second that the sum of the moments of the forces about each of these three directions also vanishes (see MOMENT). These two rules give six conditions for the equilibrium of a rigid body, three for translation, and three for rotation. Used in combination with other roots, the word statics always implies equilibrium or relative rest. Thus we have Hydrostatics (q.v.) dealing with the equilibrium of fluids, and Electrostatics (see ELECTRICITY) treating of the equilibrium of electrified bodies. See also DYNAMICS and KINETICS. Minchin's Statics (4th ed. 1890-91) is the best English treatise on the subject. See also GRAPHIC STATICS.