SAT考试是美国高中生进入美国大学的标准入学考试，包括SAT1和SAT2。SAT2是专项测验，有数学、物理、化学、生物、外语等，大部分为选择题，是可以选科的。今天我们来学习SATII物理专题分析 What Are Forces，希望对大家的复习有所帮助。

　　Whenever we lift something, push something, or otherwise manipulate an object, we are exerting a force. A force is dined very practically as a push or a pull—essentially it’s what makes things move. A force is a vector quantity, as it has both a magnitude and a direction.

　　In this chapter, we will use the example of pushing a box along the floor to illustrate many concepts about forces, with the assumption that it’s a pretty intuitive model that you will have little trouble imagining.

　　Physicists use simple pictures called free-body diagrams to illustrate the forces acting on an object. In these diagrams, the forces acting on a body are drawn as vectors originating from the center of the object. Following is a free-body diagram of you pushing a box into your new college dorm with force F.

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