Rotational Dynamics 8.3. Newton’s Second Law of Rotation Net positive torque, counterclockwise acceleration. Net negative torque, clockwise acceleration.

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