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Unformatted text preview: Chapter 13 Study Guide for Torque 13.1 Torque Skill 13.1 Understand what torque is and what quantities go in to determining it Definition of Torque: Torque is the ability of a force to rotate an object. Whereas the application of a force causes a change in linear momentum , the application of a torque causes a change in angular momentum . The value for the torque caused by an applied force depends on the magnitude, direction, and point of application of that force. Torque increases as: 1) the magnitude of the applied force increases. 2) the point of application of the applied force is moved further away from the axis of rotation. 3) the direction of the force becomes more nearly perpendicular to the radius vector. Look at the seesaw example in the book (Figures 13.2 and 13.3) to understand why the torque depends on the above quantities. Like force, torque can be positive or negative. It is conventional to define a torque that causes a counter- clockwise rotation as positive , and one that causes a clockwise rotation as negative . Only the component of the force perpendicular to the radius vector contributes to the torque, so it is useful to define a quantity called the moment arm . The moment arm of a force about an axis is the perpendicular distance from that axis to the line of action of that force. The torque can be written simply as the product of the moment arm and the applied force. 13.2 Free rotations Skill 13.2 Understand the characteristics of free rotations. If the rotation of an object is not constrained by a physical axis or by external constraints, then it is called a free rotation . In free rotations, an object always rotates about its center of mass. As a result, problems involving free motion can be split into two parts: one dealing with the translational motion of the center of mass and one dealing with the rotational motion of the object about its center of mass. The center of mass moves like a particle with the objects total mass. Look at Figure 13.7. 1 13.3 Extended free body diagrams Skill 13.3 Be able to draw extended free-body diagrams. Here is the procedure for drawing a free-body diagram: 1.) First draw a standard free-body diagram. We can use this to determine the translational motion of the center of mass....
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