Transcript Powerpoint
6 Circular Motion, Orbits, and Gravity © 2010 Pearson Education, Inc. Slide 6-2 © 2010 Pearson Education, Inc. Slide 6-3 © 2010 Pearson Education, Inc. Slide 6-4 © 2010 Pearson Education, Inc. Slide 6-5 Uniform Circular Motion The acceleration of uniform circular motion points to the center of the circle. Thus the acceleration vector has only a radial component ar. This acceleration is conveniently written in the rtz-coordinate system as © 2010 Pearson Education, Inc. Dynamics of Uniform Circular Motion The usefulness of the rtzcoordinate system becomes apparent when we write Newton’s second law in terms of the r-, t-, and zcomponents, as follows: © 2010 Pearson Education, Inc. Summary © 2010 Pearson Education, Inc. Slide 6-41 EXAMPLE The acceleration of an atomic electron QUESTION: © 2010 Pearson Education, Inc. EXAMPLE The acceleration of an atomic electron © 2010 Pearson Education, Inc. EXAMPLE The acceleration of an atomic electron © 2010 Pearson Education, Inc. Reading Quiz 1. For uniform circular motion, the acceleration A. B. C. D. E. is parallel to the velocity. is directed toward the center of the circle. is larger for a larger orbit at the same speed. is always due to gravity. is always negative. © 2010 Pearson Education, Inc. Slide 6-6 Answer 1. For uniform circular motion, the acceleration A. B. C. D. E. is parallel to the velocity. is directed toward the center of the circle. is larger for a larger orbit at the same speed. is always due to gravity. is always negative. © 2010 Pearson Education, Inc. Slide 6-7 Reading Quiz 2. When a car turns a corner on a level road, which force provides the necessary centripetal acceleration? A. B. C. D. E. Friction Tension Normal force Air resistance Gravity © 2010 Pearson Education, Inc. Slide 6-8 Answer 2. When a car turns a corner on a level road, which force provides the necessary centripetal acceleration? A. B. C. D. E. Friction Tension Normal force Air resistance Gravity © 2010 Pearson Education, Inc. Slide 6-9 Turning the corner © 2010 Pearson Education, Inc. Fictitious Forces • If you are riding in a car that makes a sudden stop, you may feel as if a force “throws” you forward toward the windshield. • There really is no such force. • Nonetheless, the fact that you seem to be hurled forward relative to the car is a very real experience! • You can describe your experience in terms of what are called fictitious forces or pseudo forces. . © 2010 Pearson Education, Inc. Centrifugal Force • If the car you are in turns a corner quickly, you feel “thrown” against the door. • The “force” that seems to push an object to the outside of a circle is called the centrifugal force. • This is caused by your inertia pressing you against the door © 2010 Pearson Education, Inc. Conical Pendulum A conical pendulum is formed by attaching a 500 g mass to a 1 m long string, then allowing the mass to move in a circular radius of 20 cm. The string traces out the surface of a cone, hence the name. a. What is the tension in the string? b. What is the mass's frequency in RPM? © 2010 Pearson Education, Inc. Slide 6-12 Bug on a CD A bug crawls outward from the center of a compact disc spinning at 175 revolutions per minute. The coefficient of static friction between the bug's sticky feet and disk is 0.9. How far does the bug get from the center before slipping off ? © 2010 Pearson Education, Inc. Slide 6-12 Loop the Loop Consider a ball on a string making a vertical circle. • Draw a free-body diagram of the ball at the top and bottom of the circle • Rank the forces in the two diagrams. Be sure to explain the reasoning behind your rankings • Find the minimum speed of the ball at the top of the circle so that it keeps moving along the circular path • What would happen if the speed was less than the minimum? • What would happen if the speed was more than the miniumum? © 2010 Pearson Education, Inc. Slide 6-12 Keep the Water in the Bucket © 2010 Pearson Education, Inc. Slide 6-12