Rotational Inertia 8.2

TEKS 2C, 3A, 4B, 4C

Center of Mass Center of mass – point at which all the mass of the body can be considered to be concentrated when analyzing translational motion. For a free body in which the only force acting on it is gravity, the point around which the object will rotate. Animation: http://my.hrw.com/sh/hf2/0030724864/student/ch08/sec02/qc01/hf208_02_q01fs.htm

Rotational and translational motion can be combined Stick rotate about its center of mass. The center of mass moves as a point mass; moves as a projectile.

Moment of Inertia Moment of inertia – a measure of the object’s resistance to a change in its rotational motion. The rotational analog of mass Depends on the distribution of the mass. Calculating the moment of inertia In general, the further a given mass is from the axis of rotation, the more difficult it is to change the rotational motion. Animation: http://my.hrw.com/sh/hf2/0030724864/student/ch08/sec02/qc02/hf208_02_q02fs.htm

Note that for a given mass at a given radius from the axis of rotation, it does not matter how the mass is distributed. Units for moment of inertia (I ): kg•m2

Rotational Equilibrium Equilibrium requires zero net force and zero net torque. F = 0  = 0 Second condition for equilibrium – dependence of equilibrium on the absence of torque. Animation: http://my.hrw.com/sh/hf2/0030724864/student/ch08/sec02/qc03/hf208_02_q03fs.htm

Practice 8B, #s 1 and 3 Section 8.2 Review, p. 289