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Chapter 13 Rotation of a Rigid Body. 13.1 Rotational kinematics 13.2 Center of mass 13.3 Torque 13.4 Rotational dynamics 13.5 Rotation about a fixed axis 13.6 *Rigid-body equilibrium 13.7 Rotational energy.
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Chapter 13 Rotation of a Rigid Body 13.1 Rotational kinematics 13.2 Center of mass 13.3 Torque 13.4 Rotational dynamics 13.5 Rotation about a fixed axis 13.6 *Rigid-body equilibrium 13.7 Rotational energy
Stop to think 13.1 page 373Stop to think 13.2 page 379Stop to think 13.3 page 383Stop to think 13.5 page 391 • Example 13.2 page 373 • Example 13.6 page 380 • Example 13.9 page 384 • Example 13.14 page 391 • Example 13.15 page 396 • The great Downhill Race Page 395
Angular velocity and angular acceleration • Angular velocity • The sign convention is that ù is positive for counterclockwise (ccw) rotation, negative for clockwise (cw) rotation. • Angular acceleration Here á is angular acceleration
Angular velocity and acceleration • Question: • What is the angular speed of ladybug1and 2 • What is the ratio of linear speed of ladybug2 to ladybug1 • What is the ratio of the centripetal • acceleration of ladybug2 to ladybug1
Torque • The ability of a force to cause a rotation depends on three factors • (1) the magnitude F of the force • (2) the distance r from the point of application to the pivot • (3) The angle at which the force is applied
Quick quiz: The rods all have the same length and are pivoted at the dot. Rank in order, From largest to smallest, the five torques.
Rank in order, from largest to smallest , the angular acceleration áa to áe
Moment of Inertial In general case: For a continuum mass object, sum becomes integral: Rotation about a Fixed Axis
Rigid-body Equilibrium • For a rigid body in total equilibrium, there is no net torque, about any point • Pick any point you wish as a pivot point. The Net torque about this point is zero
A student holds a meter stick straight out with one or more masses dangling from it. Rank in order, from most difficult to least difficult, how hard it will be for the student to keep the meter stick from rotating C > d > a = b
Rotational energy • The object’s rotational energy is:
Kinetic energy of a rolling object • K = K(rotation) + K(cm)