English: Animated diagram showing simple harmonic motion defined as the projection on the axis of a point moving at a constant speed in a circle about the origin. The righthand diagram shows a point (black) rotating in a circle of radius A about the origin. The angle it makes with the x-axis at any time t is ωt, where ω is its angular velocity in radians per second. Its projection on the x-axis (blue) is the cosine function y(t) = Acos(ωt) while its projection on the y-axis (red) is the sine function y(t) = Asin(ωt). The lefthand diagram shows the motion plotted as a function of ωt.