Mathematical Methods · radians · manipulative

Radian measure — arc equals radius

One radian is the central angle whose arc has the same length as the radius. Drag θ and watch arc = rθ — marks accumulate toward a full turn of 2π.

radius r arc angle θ radian marks

Drag the angle handle on the rim · scroll to zoom · drag background to pan

Central angle

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2.5

Linked measures

Working

Radians measure arc length in radius-units — θ = 1 means the arc is exactly one radius long. A full turn is 2π radians.