AP Physics 1 Rotational Motion Vocab

Rotational Motion

The motion of objects that spin about an axis, like a blade assembly or wind turbine

Angular Position

The angle theta used to describe the motion of a particle around a circle; it is the angle theta from the positive x-axis, and is useful since the particle travels with a fixed radius r

Angular Displacement

The angle through which an object moves on a circular path; an angle in radians between the initial and final angular positions (theta final - theta initial)

Angular Velocity (w)

The angular displacement through which the particle moves each second; w = ∆theta/∆t and w = (angular displacement)/(change in time)

Constant for a particle moving with uniform circular motion

Angular Speed

The absolute value/magnitude of the angular velocity; a positive value irrespective of the particle's direction of rotation

Rigid Body

An extended object whose size and shape do not change as it moves; an example is a bycicle wheel

Angular Acceleration

The slope of the angular velocity s time graph; the expression of the change in angular velocity that a spinning object undergoes per unit time; a net torque is the cause of an angular acceleration

Torque

Measures the "effectiveness" of a force at causing an object to rotate about a pivot; torque is the rotational equivalent of force

Moment Arm

The line that is in the direction of the force and passes through the point at which the force acts is the line of action. The perpendicular distance from this line to the pivot is called the moment arm

Center of Gravity

The gravitational torque can be calculated by assuming that the net force of gravity (the object's weight w) acts as a single special point on the object (known as the center of gravity)

Moment of Inertia

The quantity mr^2, which is the proportionality constant between angular acceleration and net torque; in kg•m^2; depends on the axis of rotation; is the rotational equivalent of mass

Rolling

A combination motion in which an object rotates about an axis that is moving along a straight line trajectory

Rolling Constraint

The basic link between rotation and translation for objects that roll without slipping; the point on the bottom of a rolling object is instantaneously at rest

Angular Momentum

The quantity of rotation of a body, which is the product of its moment of inertia and its angular velocity; units are kg•m^2/s

Law of Conservation of Angular Momentum

The angular momentum of a rotating object subject to no net external force is a constant. The final angular momentum Lf is equal to the initial angular momentum Li

Rotational Kinetic Energy

The kinetic energy due to rotation; Krot = 1/2Iw^2

Static Equilibrium

For an object to be in static equilibrium, the net torque about every point must be zero; you can pick any point you wish as a pivot point for calculating the torque; the clockwise torque due to the weight is exactly balanced by the counterclockwise torque due tot he force n.