Physics Vocabulary Sheet: Rotational Motion
1. Angular Displacement: the rotational equivalent of displacement (Δx), the angle an object has
traveled through during circular motion
Symbol: θ or Δθ (Greek letter - theta)
Units: radians (rad) or degrees (°)
Phrases: how far has the object rotated, distance, displacement
Words: angle, rotational displacement, rotational distance, distance from starting point
Equation:  
s
, s = arc length, and r = radius or distance from axis of rotation
r
2. Angular Velocity or Angular Speed: the rate of speed or how fast/slow an object moves at
during circular motion, the rotational equivalent of velocity (v)
Symbol: ω or Δω initial angular velocity:  i , final angular velocity:  f (Greek letter – omega)
Units: radians per second (rad/s)
Phrases: how fast, at what rate does it travel, at what rate does it move
Words: angular speed, angular velocity, angular rate of travel, angular rate of movement, final
angular speed, initial angular speed, final angular velocity, and initial angular velocity, rotational
speed
Equation:  avg 

t
3. Angular Acceleration: the angular rate of change in the speed or velocity; how fast/slow an
object is speeding up or slowing down during circular motion; rotational equivalent of
acceleration (a)
Symbol: α (Greek letter – alpha)
 rad 
2 
 s 
Units: radians per second squared (rad/s^2) or 
Phrases: rate of change in angular velocity, changes angular velocity, changes angular speed,
accelerates, speeds up, slows down, brakes, falls in a circular path, acceleration around the axis of
rotation
Words: angular acceleration, rotational acceleration, circular acceleration
Equation:  avg 

t
4. Centripetal Acceleration: acceleration directed inward toward the center or axis of rotation
due to circular motion
Symbol: a c
m
2 
s 
Units: meters per second squared (m/s^2) or 
Phrases: inward acceleration due to circular motion, inward acceleration, acceleration toward the
center of rotation, acceleration toward the axis of rotation
Words: centripetal acceleration
2
Equation: ac 
vt
or ac  r 2
r
5. Tangential Velocity or Tangential Speed: linear (straight-line) speed of an object directed
along the tangent to the object’s circular path
Symbol: v t or v
Units: meters per second (m/s)
Phrases: instantaneous linear speed tangent to the circle, tangential speed about a point rotating
around an axis, rotational tangential velocity/speed
Words: tangential speed, tangential velocity
Equation: vt  r
6. Tangential Acceleration: instantaneous linear (straight-line) acceleration of an object directed
along the tangent to the object’s circular path
Symbol: a t
m
2 
s 
Units: meters per second squared (m/s^2) or 
Phrases: instantaneous linear acceleration tangent to the circle, tangential acceleration about a
point rotating around an axis, rotational tangential acceleration
Words: tangential acceleration
Equation: at  r
7. Force that maintains circular motion (Centripetal Force): the force directed toward the
center of a rotating object that keeps it moving in a circular path
Symbol: Fc
Units: Newtons (N)
Phrases: force directed toward the center, inward force, force due to rotation, force toward the
center/axis of rotation, force that maintains circular motion
Words: centripetal force, force of circular motion
2
mvt
Equation: F c 
or Fc  mr 2
r