Rotational Dynamics
8.3
Newton’s Second Law of Rotation
Net positive torque, counterclockwise acceleration.Net negative torque, clockwise acceleration.
When net torque is zero:
Object rotates at constant velocity,Or if object at rest, object does not rotate.
MomentumObjects also resist change in their rotational motion.Rotating objects have inertia, and have a momentum assoc. with rotation.
Unit: kg•m2/s
Angular momentum is conservedWhen no net torque is acting on an object or objects, angular momentum is conserved – law of conservation of angular momentum.
A B
LA = LB
I = I Animation: http://my.hrw.com/sh/hf2/0030724864/student/ch08/sec03/qc04/hf208_03_q04fs.htm
Kinetic EnergyRotating objects have KE associated with their angular speed.
Unit: J
Animation: http://my.hrw.com/sh/hf2/0030724864/student/ch08/sec03/qc05/hf208_03_q05fs.htm
Mechanical Energy is Conserved
Answer to Sample Problem 8C: 13 N•mAnswers to Problem #2 for Practice 8C:2.) –8.1 N•m
Answer to Sample Problem 8D: 0.24 rad/sAnswers to Even Problems for Practice 8D:2.) 24 rad/s4.) 9.1 x 102 m/s
Answer to Sample Problem 8E: 5.29 m/sAnswer to Problem #2 from Practice 8E:2.) 12.0 m/s