Periodic functions > Radians

Point $P$ moves along the unit circle (circle with radius $1$). The corresponding angle of rotation $\alpha $ is positive when you move counterclockwise, negative if when you move clockwise. It can have any value. The height $h$ of $P$ with respect to the horizontal axis is $h=sin\left(\alpha \right)$.

For a more suitable graph we rather express the angle of rotation
$\alpha =x$ in radians.

The angle then corresponds to the length of the arc on the unit circle (the blue part
of the circle).

$360\xb0$ correponds to
$2\pi $ radians.

This standard sine graph is periodical with period $2\pi $.

Look at the applet: Sine graph