← Angular velocity and the speed on the circle

The angular velocity equation

A turbine blade sweeps 6 radians in 2.0 s, turning steadily.

What is its angular velocity?

The sweep shares out evenly over the time: each second gets 6 / 2.0 = 3 radians.

The turbine blade's sweep, sharedquantityvalueangular displacement Δθ6 radtime taken Δt2.0 seach second's share, 6 / 2.03 rad
6 radians over 2.0 s is 3 radians each second: ω = 3 rad/s.

So the blade's angular velocity is ω = 3 rad/s: it sweeps out 3 radians each second.

One equation says that division for every rotation.

angular velocity = angular displacement ÷ time taken

In symbols: ω = Δθ/Δt.

You have seen this shape before: a = Δv/Δt divides a change by the time it takes. ω = Δθ/Δt is the same grammar, with the swept angle as the change.

ω comes out in rad/s when Δθ is in radians, and in °/s when Δθ is in degrees; Δt is in seconds either way.

Symbol keysymbolnameunitωangular velocityrad/s (or °/s)Δθangular displacement sweptrad (or °)Δttime takens
ω = Δθ/Δt, with each symbol named.

A rotor sweeps 10 radians in 4.0 s, turning steadily. Enter its angular velocity in rad/s.

Coral says: 'A wheel with an angular velocity of 5 rad/s sweeps out 5 radians each second.' Is Coral correct?

A carousel sweeps 450° in 5.0 s, turning steadily. Calculate its angular velocity.

A degrees case through the same divisionquantityvalueangular displacement Δθ450°time taken Δt5.0 seach second's share, 450 / 5.090°
The carousel's 450° over 5.0 s is 90° each second: ω = 90°/s.

Write down the values:

Δθ = 450°, Δt = 5.0 s, ω = ?

Write down the equation:

ω = Δθ/Δt

Substitute in the values, and calculate:

ω = 450 / 5.0 = 90

The carousel's angular velocity is 90°/s.

A mixer blade's angular velocity is 7 rad/s. State what that means.

ω is the angle swept each second.

The blade sweeps out 7 radians each second.

Reading an angular velocitystatementmeaningω = 7 rad/s7 radians swept each secondω = 3 rad/s3 radians swept each second
rad/s reads as radians swept in each second.

Your turn

A fairground ride sweeps 270° in 6.0 s, turning steadily. Enter its angular velocity in °/s.

Two merry-go-rounds turn steadily for the same time. The first sweeps twice the angle the second sweeps. How do their angular velocities compare?

An exercise bike's wheel turns at an angular velocity of 12 rad/s. Which statement is correct?

Which equation gives the angular velocity?