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# Chapter 12 rotational motion

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Physics notes ch 12

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### Chapter 12 rotational motion

1. 1. CHAPTER 12 ROTATIONAL MOTION Rotational objects tend to keep rotating while non-rotating objects tend to remain non-rotating.
2. 2. Chapter 12 Key Terms <ul><li>Rotational Inertia (p. 213) The resistance of an object to changes in its rotational motion is called rotational inertia. </li></ul><ul><li>Linear Momentum (p.219) is the product of the mass and the velocity of an object. </li></ul><ul><li>Angular Momentum (p. 219)is defined as the product of rotational inertia, I and rotational velocity, w. </li></ul><ul><li>Angular momentum = rotational inertia (I)x rotational velocity (w) </li></ul><ul><li>Rotational Velocity (p. 219) is a vector whose magnitude is the rotational speed. </li></ul><ul><li>Law of conservation of angular momentum ( p. 221) states that if no unbalanced external torque acts on a rotating system, the angular momentum of that system is constant. </li></ul>
3. 3. 12.1 Rotational Inertia <ul><li>The greater the rotational inertia, the more difficult it is to change the rotational speed of an object. </li></ul><ul><li>The resistance of an object to changes in its rotational motion is called rotational inertia, or moment of inertia. </li></ul><ul><li>A torque is required to change the rotational state of motion of an object. </li></ul><ul><li>Rotational inertia depends on mass and how the mass is distributed. The greater the distance between an object’s mass concentration and the axis of rotation, the greater the rotational inertia. </li></ul>
4. 4. 12 .1 Rotational Inertia Cont. <ul><li>A short pendulum has less rotational inertia and therefore swings back and fourth more frequently than a long pendulum. Likewise, bent legs swing back and forth more easily than outstretched legs. </li></ul><ul><li>Formulas to calculate rotational inertia for different objects vary and depend on the shape of an object and the location of the rotational axis. </li></ul>
5. 5. 12.2 Rotational Inertia and Gymnastics <ul><li>The three principal axes of rotation in the human body are the longitudinal axis, the transverse axis, and the medial axis. </li></ul><ul><li>The three axes of rotation in the human body are at right angles to one another. All three axes pass through the center of gravity of the body. </li></ul><ul><li>The vertical axis that passes from head to toe is the longitudinal axis. Rotational inertial about the axis is increased by extending a leg or the arms. </li></ul>