# Angular Velocity Formula

#### Angular Velocity is a measure of how quickly an object moves through an angle. It is the change in angle of a moving object (measured in radians), divided by time. Angular velocity has a magnitude (a value) and a direction.

*Angular velocity = (final angle) – (initial angle) / time = change in position/time*

*ω = (θ _{f} – θ_{i}) / t*

*ω* = angular velocity

*θ _{f}* = the final angle

*θ _{i}* = the initial angle

*t* = time

*Δθ* = short form for ‘the change in angle’

**Angular Velocity Formula Questions:**

#### 1) The second hand of a clock takes 30 seconds to move through an arc of 180 degrees. What is the angular velocity?

**Answer:** The second hand starts at θ_{i} = 0 degrees and moves to θ_{f} = 180 degrees from the point of origin. 180 degrees = 1/2 of a full revolution, so θ_{f} = (0.5 x 2 π). (360 degrees is 2π rad). The time it takes for the second hand to move through 180 degrees is 30 seconds, so t = 30 s. We can now calculate the angular velocity.

**Answer:**

#### ω = (θ_{f} – θ_{i}) / t

#### ω = (0.5 x 2π ) rad / 30 s

#### ω = (π) rad / 30 s = 3.14 rad / 30 s

#### ω = 0.105 rad/s

#### 2) You tour a jewelry-polishing facility. Their polishing wheel moves at 150 revolutions per minute. What is it’s angular velocity?

**Answer:** Each revolution is 2π rad. The angle (θ_{f} – θ_{i}) = (150) x (2π rad). The time, t, is 1 min, or t = 60 s. Use the formula for angular velocity.

**Answer:**