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In physics, net force is the ''overall'' force acting on an object. In order to calculate the net force, the body is isolated and interactions with the environment or other constraints are represented as forces and torques in a free-body diagram. The net force does not have the same effect on the movement of the object as the original system forces, unless the point of application of the net force and an associated torque are determined so that they form the resultant force and torque. It is always possible to determine the torque associated with a point of application of a net force so that it maintains the movement of the object under the original system of forces. With its associated torque, the net force becomes the ''resultant force'' and has the same effect on the rotational motion of the object as all actual forces taken together.〔Symon, Keith R. (1964), Mechanics, Addison-Wesley, 〕 It is possible for a system of forces to define a torque-free resultant force. In this case, the net force when applied at the proper line of action has the same effect on the body as all of the forces at their points of application. It is not always possible to find a torque-free resultant force. == Total force == The sum of forces acting on a particle is called the total force or the net force. The net force is a single force that replaces the effect of the original forces on the particle's motion. It gives the particle the same acceleration as all those actual forces together as described by the Newton's second law of motion. Force is a vector quantity, which means that it has a magnitude and a direction, and it is usually denoted using boldface such as F or by using an arrow over the symbol, such as . Graphically, a force is represented as line segment from its point of application ''A'' to a point ''B'' which defines its direction and magnitude. The length of the segment ''AB'' represents the magnitude of the force. Vector calculus was developed in the late 1800s and early 1900s. The parallelogram rule used for the addition of forces, however, dates from antiquity and is noted explicitly by Galileo and Newton.〔Michael J. Crowe (1967). ''A History of Vector Analysis : The Evolution of the Idea of a Vectorial System''. Dover Publications (reprint edition; ISBN 0-486-67910-1).〕 The diagram shows the addition of the forces and . The sum of the two forces is drawn as the diagonal of a parallelogram defined by the two forces. Forces applied to an extended body can have different points of application. Forces are bound vectors and can be added only if they are applied at the same point. The net force obtained from all the forces acting on a body will not preserve its motion unless they are applied at the same point and the appropriate torque associated with the new point of application is determined. The net force on a body applied at a single point with the appropriate torque is known as the resultant force and torque. 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「Net force」の詳細全文を読む スポンサード リンク
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