← Describing rotation

Converting angle units

The same turn can be written three ways: a rotating stage platform that turns 1.5 revolutions has swept 540°, and also 3π radians. Converting among the three is one multiply or divide, once you know the linking facts.

One revolution is one full turn: 360°.

One revolution is also 2π radians.

One full turn, three waysunitone full turnrevolutions1 revdegrees360°radians2π rad, about 6.28 rad
One full turn: 1 revolution, 360°, 2π radians.

Half a turn links degrees and radians directly: 180° = π radians.

To convert, write down the fact that links the two units, then multiply or divide by it.

Revolutions to degrees: multiply by 360. Degrees to revolutions: divide by 360.

Revolutions to radians: multiply by 2π. Radians to revolutions: divide by 2π.

Degrees to radians: multiply by π and divide by 180. Radians to degrees: multiply by 180 and divide by π.

The linking factsconversionfact to userevolutions and degrees1 rev = 360°revolutions and radians1 rev = 2π raddegrees and radians180° = π rad
Each conversion uses one linking fact: multiply one way, divide the other.

π is the calculator's π button, about 3.14159, never a rounded 3.

The stage platform turns 1.5 revolutions. Convert that angular displacement to degrees.

Write down the fact:

1 revolution = 360°

Multiply:

degrees = revolutions × 360

1.5 × 360 = 540

The platform swept 540°.

Convert the platform's 540° to radians.

Write down the fact:

180° = π radians

Divide to count the half-turns, then attach π:

radians = degrees × π / 180

540 × π / 180 = 3π, about 9.42

The platform swept 3π radians, about 9.42 rad.

Quick-fire drill

A ballet dancer turns 2.5 revolutions. Enter the angular displacement in degrees.

A valve wheel turns through 72°. Enter the angular displacement in revolutions.

A lazy Susan turns 0.75 revolutions. Enter the angular displacement in radians, to 2 decimal places.

A telescope dome turns through 2.62 radians. Enter the angular displacement in degrees, to the nearest degree.

A camera mount turns through 60°. Enter the angular displacement in radians, to 2 decimal places.

A satellite dish sweeps through 7.85 radians while tracking. Enter the angular displacement in revolutions, to 2 decimal places.

Your turn

A revolving restaurant door turns 1.2 revolutions as Bruno walks through. Enter the door's angular displacement in degrees.

A wind vane swings through 45°. Enter the angular displacement in radians, to 2 decimal places.

During one test, a washing machine drum sweeps through 10.5 radians before pausing. Enter the drum's angular displacement in revolutions, to 2 decimal places.