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Chapter 9 Rotational Dynamics. Torque – any force that can cause a rotation. A net force causes an acceleration. Torque = Force x Lever Arm. A net torque causes an rotation. Lever Arm – perpendicular distance b/w line of action & axis of rotation.
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Torque – any force that can cause a rotation A net force causes an acceleration. Torque = Force x Lever Arm A net torque causes an rotation.
Lever Arm – perpendicular distance b/w line of action & axis of rotation. Line of Action – extended line drawn through force.
Equilibrium – net external forces and torques are zero. No translational acceleration (a)No angular acceleration (α)
Center of Gravity (C.O.G.) - Point on object where all weight is concentrated. Same as center of mass for most objects. Balance point of object; object will tip over (rotate) when c.o.g. is beyond support base.
An irregular object acts as if all of its mass is at the center of mass.
If the c.o.g. is above the base, the object will not topple over.
measure of inertia. Mass - Inertia - Resistance to change in motion. Newton’s 2nd Law A bigger mass requires more force for the same acceleration.* *rotating objects acquire an additional amount of inerita (called rotational inertia)
These objects have the same mass. it must have less inertia Which would be easier to rotate? Rotational inertia depends on mass distribution.
These objects have the same mass. it must have less inertia Which would be easier to rotate? Rotational mass depends on axis of rotation.
Rotational Inertia (I) – inertia of a rigid rotating body w/ respect to axis of rotation. AKA ‘moment of inertia’ Depends on mass distribution and axis of rotation.
2nd Law for Rotational Motion Angular acceleration (rad/s2) Torque (N∙m) Moment of Inertia (kg∙m2) Formulas for I are on page 251
WorkRotational Work Kinetic EnergyRotational KE
Momentum - Angular Momentum - Conservation of Angular Momentum The total L of a system remains constant if the net external torque acting on the system is zero.
