# Shared Flashcard Set

## Details

Chapter 9
Rotational Dynamics
22
Physics
02/21/2015

Term
 line of action
Definition
 an extended line drawn collinear with the force
Term
 lever arm
Definition
 the distance "l" between the line of action & the axis of rotation, measured on a line that is perpendicular to both
Term
 What is the direction of torque?
Definition
 the torque "tau" is positive when the force tends to produce a counterclockwise rotation about the axis, & negative when the force tends to produce a clockwise rotation
Term
 SI unit of torque
Definition
 newton x meter (N x m)
Term
 Can the same magnitude produce different torques?
Definition
 yes!
Term
 external forces
Definition
 forces from external agents; the only forces used when calculating the net force
Term
 When is a rigid body in equilibrium?
Definition
 if it has zero translational acceleration & zero angular acceleration; the sum of the externally applied forces is zero & the sum of the externally applied torques is zero
Term
 Why is the choice of axis arbitrary in equilibrium?
Definition
 if an object is in equilibrium, it is in equilibrium with respect to any axis whatsoever
Term
 center of gravity ("cg")
Definition
 a definite point chosen at which the weight acts on an object for the purpose of calculating the torque
Term
 Where does the center of gravity lie for any symmetrically shaped & uniform object?
Definition
 at its geometrical center
Term
 SI unit of moment of inertia
Definition
 kg(m^2)
Term
 What requirement must be met in order to use the rotational analog of Newton's second law for a rigid body rotating about a fixed axis (sum of the torques = moment of inertia x angular acceleration)
Definition
 alpha must be expressed in rad/s^2
Term
 rigid
Definition
 the distances that locate each particle do not change during the rotational motion
Term
 When calculating the sum of the torques, it is necessary to include only the _____, those applied by agents outside the body
Definition
 external torques
Term
 What requirement must be met to determine rotational work (rotational work = constant torque x angle)
Definition
 theta must be expressed in radians
Term
 SI unit of rotational work
Definition
 joule (J)
Term
 What requirement must be met to determine to rotational kinetic energy (rotational kinetic energy = 1/2(moment of inertia x angular speed^2))
Definition
 omega must be expressed in rad/s
Term
 SI unit of rotational kinetic energy
Definition
 joule (J)
Term
 What is the analogous concept to linear momentum in terms of rotational motion?
Definition
 angular momentum (L)
Term
 What requirement must be met to determine the angular momentum (angular momentum = moment of inertia x angular velocity)
Definition
 omega must be expressed in rad/s
Term
 SI unit of angular momentum
Definition
 kg(m^2)/s
Term
 principle of conservation of angular momentum
Definition
 the total angular momentum of a system remains constant if the net average external torque acting on the system is zero; total angular momentum of a system is conserved
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