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Statics is the branch of mechanics that is concerned with the analysis of loads (force and torque, or "moment") on physical systems in static equilibrium, that is, in a state where the relative positions of subsystems do not vary over time, or where components and structures are at a constant velocity. When in static equilibrium, the system is either at rest, or its center of mass moves at constant velocity. By Newton's first law, this situation implies that the net force and net torque (also known as moment of force) on every part of the system is zero. From this constraint, such quantities as stress or pressure can be derived. The net forces equaling zero is known as the ''first condition for equilibrium,'' and the net torque equaling zero is known as the ''second condition for equilibrium.'' See statically determinate. ==Vectors== A scalar is a quantity, such as mass or temperature, which only has a magnitude. A vector has a magnitude and a direction and obeys the parallelogram law. There are several notations to identify a vector, including: *A bold faced character V *An underlined character V *A character with an arrow over it . Vectors are added using the parallelogram law or the triangle law. Vectors contain components in orthogonal bases. Unit vectors i, j, and k are, by convention, along the x, y, and z axes, respectively. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Statics」の詳細全文を読む スポンサード リンク
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