Physics Vocabulary Sheet: Rotational Motion and Gravitational Force
You need to be able to identify words in the problems so you can figure out what information you have and what you need to find. Below are some words that can point you toward success in solving problems.
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)
Units: radians per second squared ( rad/s^2 ) or rad s
2
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
Units: meters per second squared (m/s^2) or m s 2

Phrases: inward acceleration due to circular motion, inward acceleration, acceleration toward the center of rotation, acceleration toward the axis of rotation
Words: centripetal acceleration
Equation: a c
 v t r
2 or a c
 r

2
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 or v t
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: v t
 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
Units: meters per second squared (m/s^2) or m s 2
Phrases: instantaneous linear acceleration tangent to the circle, tangential acceleration about a point rotating around an axis, rotational tangential acceleration
Words: tangential acceleration
Equation: a t
 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: F c
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
Equation: F c
 mv t
2 or F c
 mr
 2 r
8.
Gravitational Force: field force of attraction between particles of matter due to their mass
Symbol: F g
Units: Newtons ( N )
Phrases: force of gravity, gravitational field force, force between masses, force due to mass, force due to gravity, gravitational attraction
Words: gravitational force
Equation: F g

G m
1 r m
2
2
, where G

6 .
673

10

11
N
 m kg
2
2