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Unformatted text preview: Review Notes For Exam 4 SAR Physics AM Kolchin I. Circular Motion 1. Circular motion is done about an axis : All of our discussions in class have made reference to some axis about which rotation takes place. When talking about rotational velocity, rotational accelera tion, torque, angular momentum, or rotational inertia we are always referring to some axis of rotation. 2. Rotation : Takes place about an objects internal axis. 3. Revolution : Takes place about an external axis. 4. Rotational speed ( ): angle swept out per unit time. (units: rpm, degrees/s, radians/s) For a rigid object, rotating about an axis, the rotational speed is the same at all points in the object. 5. Linear speed or tangential speed ( v ): distance cov ered per unit time. The linear speed is not the same everywhere on a rigid object, rotating about an axis. Rather, the linear speed of a point on the object is di rectly proportional to the rotational speed ( ) and the distance ( r ) of the point from the axis of rotation: v r . So if you double r , you double v ; if you double , you double v ; if you double both, then v quadruples. (Units include: m/s, mph,). 6. Centripetal Force : An object in circular motion is always changing direction. Its speed may be constant, 1 but then it is always experiencing a force that is perpen dicular to its velocity. This force is directed inward in the radial direction . We call this force centripetal force no matter what its source. Centripetal force can be caused by gravitational attraction or a string pulling inward on a whirling ball. For an object in circular mo tion about an axis, the centripetal force is related to the objects: mass ( m ), speed ( v ), and distance ( r ) from the axis by the equation: F c = mv 2 r What happens to F c if I double the objects speed, mass, or distance from the axis of rotation? Be able to an swer these and similar questions. (Units are good old fashioned newtons (N)). Note : Since F c is always perpendicular to the direc tion of v for a mass in circular motion, it never does any work on the object. Work is only done on an ob ject by the component of a force in the direction of the objects motion. Since F c is to the motion, it has no...
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This note was uploaded on 10/19/2011 for the course PHY 2020 taught by Professor Staff during the Spring '08 term at University of Florida.
 Spring '08
 Staff
 Physics, Circular Motion

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